Ethiopia•Lower Omo Valley, locality P 64; 3.6 Ma; R. Bonnefille leg.; XI.1973; Twf 17918; Tervuren collection.

The fossil is moderately well-preserved in longitudinal sections and exhibits numerous fungal hyphae and spores within the vessel lumina, suggesting the wood was likely degraded prior to mineralization. The wood exhibits diffuse porosity with indistinct growth rings (Fig. 3A, B). Vessels are solitary (51%) or arranged in radial multiples of 2 (26.4%), 3 (18%), 4 (4%), and 5 (1%). The mean tangential diameter of the vessels is 90 µm (ranging from 34 to 145 µm), with thick walls measuring 9 µm. There are 7-15 vessels per square millimeter, featuring simple, horizontal or oblique perforation plates. Vessel element lengths measure 180-270 µm; gum deposits are visible within the vessel lumina. Intervessel-pits are alternate, small (4-5 µm), and they appear to be probably vestured (Fig. 3G), vessel-ray pits are similar to intervessel-pits. The parenchyma is vasicentric, confluent, and seemingly banded, with strands likely composed of 2-4 cells. The rays are 1-3 seriate, irregular in shape, and heterocellular (Fig. 3D, H), with a frequency of 12-14 per mm (Fig. 3C, D); ray height varies (90-450 µm) and ray width range is 10-58 µm, uni-seriate rays are exclusively composed of upright cells, and pluri-seriate rays containing one or two rows of marginal upright cells. The preservation of the fossil does not allow for precise characterization of the fibres. Crystals are distinct in enlarged cells and druses are found in ray cells, and in the parenchyma cells (Fig. 3E, F).

Twf 17918 was initially attributed to Garcinia ‌huilensis ‌(Dechamps & Maes 1985). However, several anatomical features differentiate the specimen from Garcinia (Clusiaceae), including the presence of crystals in ray cells, druses in parenchyma cells, and small, vestured intervessel pits. The combination of vasicentric, confluent, and seemingly banded parenchyma, heterocellular rays with variable and abundant crystals (in enlarged cells, druses in parenchyma), are more consistent with members of the subfamily Combretoideae and the subtribe Terminaliinae (InsideWood 2004-onwards; Van Vliet 1979). Terminalia includes ten species from Ethiopia (Vollensen 1995a). Two of them, Terminalia ‌brevipes ‌Pamp. and T. ‌prunoides ‌M.A. Lawson, have uniseriate rays. We note some similarities of our fossil with Terminaliaalbida ‌Scott. Elliot, but due to the lack of description for other species, we identify Twf 17918 as Terminalia sp.

Twelve fossil wood specimens attributed to Terminali­oxylon, the morphotype close to modern Terminalia, are known in Africa since the Eocene (Bamford 2003; Boureau 1955, 1958; Dupéron-Laudoueneix 1973; El-Saadawi et al. 2014; Fessler-Vrolant 1978, 1980; Lemoigne 1978; Lemoigne & Beauchamp 1972; Mädel-Angeliewa & Müller-Stoll 1973; Wheeler et al. 2007). None of them match with the Shungura fossil wood. Another fossil specimen (Twf 17919) from the Usno Formation, Omo valley, north of the Shungura Formation and extracted from Unit-19 dated 3.21 Ma) was attributed to Terminalia ‌(Jolly-Saad & Bonnefille 2023). But the Usno specimen differs from the Shungura one by having less axial parenchyma and septate fibres. Twf 17918 from the Shungura Formation may represents a different and an older species than that recorded at Usno, although designated Terminalia sp.

Ethiopia•Lower Omo Valley, locality P 64 sect. 19a; Unit A-1-1, 3.6 Ma; Twf 17873; Jean de Heinzelin leg.; Tervuren collection.

The cross section is very poorly preserved, with fungi visible in vessels. Growth rings are absent. Wood is diffuse-porous. Vessels are solitary (37 %) or in radial multiples of 2 (37 %), 3 (18 %), 4 (5 %), 5 (1%) (Fig. 4A). Vessels are rounded in outline or slightly oval. Mean tangential diameter of 90 µm, range 76-103 µm, 11-16 per mm². Perforation plates are exclusively simple; intervessel-pits are alternate, minute, less than 4 µm and densely distributed (Fig. 4E); vessel-ray pits are indistinct. Vessel wall thickness is about 9 µm. Vessel element length is not distinct.

Rays are 2-3 seriate with short uniseriate ends, uniseriate rays are rare, 6-8 per mm, heterocellular, composed of procumbent body cells with 1-4 or more than 4 rows of square and upright cells. Ray height range is between 157-421 µm (11-37 cells); width is between 17-21 µm. Gum or other deposits are present in vessels (Fig. 4C, D). Axial parenchyma is confluent, anastomosed in irregular and wavy bands. Parenchyma strands are composed of 3-4 or 5-8 cells. Fibres are septate or not septate, with diameter range of 9-18 µm, medium to thick-walled; pits are not observed. Mineral inclusions are visible in all ray cells and in parenchyma (Fig. 4D).

The combination of diffuse-porous wood, with randomly arranged vessels, minute-small vessel-pits, predominantly paratracheal parenchyma that is vasicentric to slightly aliform, predominantly triseriate rays composed of heterocellular cells, and chambered crystalliferous axial parenchyma occur commonly in the Combretaceae or Fabaceae. Due to it’s poor preservation, the fossil cannot be identified more precisely than Combretaceae/Fabaceae gen. and sp. indet. 1.

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 64; Unit A-1-1, 3.6 Ma; R. Bonnefille leg.; R. Bonnefille 73-11; Twf 18054; Tervuren collection.

Twf 18054 structure is well preserved in transverse section, but longitudinal sections appear roughly per-mineralized and are badly preserved. Wood is diffuse-porous, growth rings marked by radially flattened latewood fibers. Vessels are mostly solitary (90%) or in radial multiple of 2-4, rounded in outline (Fig. 5A, B), with small to medium, mean tangential diameter of 108 µm (range 54-162 µm), 2-8 per mm²; vessel wall is thick (9 µm). Perforation plates are exclusively simple, horizontal to slightly oblique; intervessel-pits and vessel-ray pits are indistinct, mean vessel element length 200 µm, range 180-202 µm, tylose is not observed.

Axial parenchyma vasicentric, aliform, strands of 1-2 cells. Rays are exclusively 1-3 seriate, not storied, consisting of procumbent cells with one row of upright cells, not greatly elongated radially, 8-10 rays per mm (Fig. 5C, D). Ray height range is between 190 µm (11 cells) and 544 µm (27 cells), ray width range is 9-15 µm. Fibres are (likely) septate, walls medium to thick, no pits are observed. Crystals are distinct in ray cells and in chambered parenchyma in short chains (Fig. 5F).

The combination of diffuse-porous wood, vessels solitary and in radial multiples, mean vessel diameter greater than 100 µm, simple perforation plates, slightly heterocellular rays that can be up to 4 or more cells wide and fewer than 12 per mm, septate fibres, crystals in parenchyma, all together suggest affinity with modern Fabaceae characterized by vestured pits (Wheeler & Baas 1992). They also fit with the anatomical structure of the Mimosoideae subfamily (Evans et al. 2006) now re circumscribed into Caesalpiniodeae subfamily by the Legume Phylogeny Working Group (LPWG 2017). However, these characters also occur in the Bignoniaceae, Sapindaceae, Moraceae and Meliaceae, but the presence of vestured pits is diagnostic of Fabaceae ‌(Wheeler & Baas 1992).

Twf 18054 specimen resembles the fossil genus Mimosoxylon ‌(Müller-Stoll & Mädel 1967), but it is distinct from the five species of the genus Mimosoxylon described in Ethiopia and Africa. Mimosoxylon ‌krameriLemoignefrom the Tertiary of the Ghibe River has uniseriate rays. M. ‌calpo­calycoides ‌Lemoigne shows paratracheal vasicentric, confluent in marginal or in seemingly marginal bands axial parenchyma. Mimosoxylon ‌mbakaouense ‌Dupéron-Laudoueneix from the Tertiary of Cameroon has 1-2 seriate rays, and rare triseriate rays. M. ‌ducis-aprutii ‌(Chiarugi) has 2-3 seriate rays (Müller-Stoll & Mädel 1967). From the Pliocene in Middle Awash (Ethiopia), MA 94-73A, reported as Mimosoxylon sp., has less axial parenchyma and non-septate fibres (Jolly-Saad et al. 2012). It differs from the Shungura specimen. Other Legums fossil wood such as Legumino­xylon ouniangaense Koeniguer from the Miocene of Chad is semi-ring porous and has biseriate rays (Koeniguer 1968). L. ‌lefrancii ‌Koeniguer from the Tertiary of eastern Fezzan in the Sahara has biseriate rays (Bonnet et al. 1970). In conclusion, Twf 18054 from the Shungura Formation related to the Mimosoideae subfamily does not fit any Mimosoxylon described in the literature. We attribute this sample to Fabaceae with a special reference to Mimosoideae.

Ethiopia•Lower Omo Valley, Shungura Formation, locality O 127; Unit A-1-1, 3.6 Ma; R. Bonnefille leg.; Twf 17913; Tervuren collection.

Twf 17913 has moderate preservation and is highly mineralized with abundant fungal hyphae and spores in vessel lumina. Its structure has been partly disturbed by damage and amorphization processes. Wood is diffuse-porous with indistinct, growth rings (Fig. 6A). Vessels are solitary (40%) and in radial multiples of 2 (34%), 3 (18%), 4 (6%), 7 (1%), and clusters (1%), mean tangential diameter is 92 µm, (range 34-126 µm), vessel element range is 115 to 670 µm high, round or slightly oval in shape, 3 to 9 per mm². Tyloses are absent, gum is observed in vessels. Vessel element length varies from 135 to 368 µm. Perforation plates are exclusively simple and oblique. Minute inter-vessel pits (< 4 µm) are alternate, mostly polygonal in shape and not vestured (Fig. 6E). Vessel-ray pits are not distinct. Axial parenchyma is vasicentric with 1 or 2 rows of flattened cells, bands with 3 to 6 cells height including vessels and arranged in a reticulate pattern. Bands are irregular, wavy often anastomosing. Parenchyma strands are composed of 3-8 cells.

Rays are 1 to 5 seriate, exceptionally uni or biseriate, heterocellular (Fig. 6C, D, G), 8 to 10 per mm, irregularly storied, composed of procumbent cells with one row of upright cells (Fig. 6D). Ray height range is between 115-667 (4-31 cells), ray width range is 14-41 µm.

Fibres 5 to 18 µm in diameter have thick walls, pits are not observed, and septae clearly distinct (Fig. 6F). There are crystal inclusions in ray cells (Fig. 6G).

Twf 17913 was initially assigned to Garcinia ‌huilensis ‌Welw. ex Oliv., among the Clusiaceae ‌(Dechamps 1983). However, a comparison with the Insidewood database, anatomical atlas and Tervuren xylarium material references of Garcinia ‌huilensis (Tw 24240) do not justify such attribution. Medium vessels, winged aliform or seemingly banded or reticulate parenchyma, simple perforation plate, heterocellular rays 1-5 wide, minute non-vestured intervessel pits, septate fibres; parenchyma in numerous, wavy or nearly straight, continuous or broken lines are all characters showing greater similarities with wood of modern Meliaceae ‌DC., particularly with Entandrophragma ‌DC. Detailed anatomical descriptions exist for seven modern species of Entandophragma from Africa (Jackson 1956; Kasongo Yakusu et al. 2018). E. ‌angolense ‌DC., E. ‌congoense ‌(Pierre ex De Wild.) A. Chev., E. ‌delevoyi ‌De Wild. and E. ‌excelsum ‌(Dawe et Sprague) Sprague are characterized by continuous, regularly spaced bands of parenchyma and circum vascular aliform parenchyma, rays are 3-5 seriate with oxalate crystals in the terminal cells. E. ‌utile ‌(Dawe & Sprague) Sprague has parenchyma in continuous bands and discontinuous, sinuous in growth ring, rays are 2-3 seriate, and crystal in ray cells. E. ‌cylindricum ‌(Sprague) Sprague has continuous bands and wide bands, 10-15 pore per mm², and crystal in ray cells (Panshin 1933). E. ‌candollei ‌Harms and E. ‌palustre ‌Staner are the two species having abundant parenchyma, and silica bodies in ray cells (Lebacq 1955-1963; InsideWood 2004-onwards). But we have no information about the three modern species, Entandrophragma ‌bussei ‌Harms ex Engl., E. ‌caudatum ‌Sprague and E. ‌spicatum that have a Zambezian and Afromontane geographical distribution (Kasongo Yakusu et al. 2018).

Among the palaeobotanical species, Entandrophragmoxylon ‌boureaui ‌Louvet (Oligocene of Algeria and Miocene of Libya) is characterized by the presence of axial canals and relatively wide rays (Louvet 1963; Koeniguer & Louvet 1968). E.mkrattaense ‌Louvet and E.normandii ‌Louvet (Mio-Pliocene of Algeria), as well as another Meliaceae from the Miocene in Congo (Lakhanpal & Prakash 1970) differ from the Omo sample by the absence of septate fibers (Louvet 1968).

In conclusion, the Shungura fossil shares more common characters with extant species, notably E. ‌candollei and E. ‌palustre than with most Tertiary paleobotanical species. We assign sample Twf 17913 to Entandophragma sp. 1.

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 64 sect. 18; Member A, Unit A-1-1, 3.6 Ma; J. de Heinzelin leg.; Twf 17854, Twf 17914; Tervuren collection.

Twf 17854 is highly mineralized with abundant fungal spores present in vessels. The wood is diffuse-porous. Growth rings are fairly distinct (Fig. 7A) and delineated by a line of 1-2 cells of initial/terminal parenchyma (Fig. 7A, B). Vessels are solitary (59%) and in radial multiples of 2 (16%), 4 (5%) and 5 (1%), small to medium, circular to oval in shape and evenly distributed 4 to 16 vessels per mm², average thickness of vessel wall is 8-9 µm (Fig. 7A). Tangential diameter range is 29-92 µm (average 72 µm), Perforation plates are simple and more or less horizontal, range of vessel element length varies from 200 to 500 µm, inter-vessel pits are alternate, round to polygonal, small (< 4 µm), probably not vestured but the quality of the conservation makes it very difficult to make a decision (Fig. 7F). Vessel-ray pits are similar to intervessels-pits. Brown and dark deposits occur in vessels. Axial parenchyma is vasicentric, winged-aliform, banded or seemingly banded with 1 to 6 rows of cells, densely organized (6 to 12 bands/ mm), either regular or irregular, short or incomplete (Fig. 7B). Rays are (1)-2- 3 seriate, with variable height between 91 to 540 µm, narrow width from 9 to 40 µm) (Fig. 7C, D), not storied, numerous with 12 per mm²; uniseriate rays are rare and heterocellular composed of mixed square and upright cells (Fig. 7F). Pluriseriate rays are composed of procumbent cells and have uniseriate margins of 1 to 4 cells not strongly different in shape from the body cells, 1-2 rows of distinct upright cells. Prismatic crystals occur in the ray and in non-chambered parenchyma cells. Fibres are septate with 8-14 µm diameter width.

The earlier identification of Twf 17854 as Cryptosepalum ‌exfoliatum ‌De Wild (Fabaceae) in Dechamps (1983) does not seem appropriate to the presently observed anatomical features of the wood. In the Fabaceae, Cynometra shows great similarities with Twf 17854. However, the absence of septate fibres excludes it from the diagnosis. Comparison with the InsideWood database, reveals that the combination of traits, such as wood diffuse-porous with small vessels, winged aliform or seemingly banded parenchyma, simple perforation plate; 1-2-(3) seriate heterocellular rays, minute vessels-pits, septate fibres are also found in the Sapindaceae, Meliaceae and Fabaceae, but not in Cryptosepalum. The Sapindaceae have seemingly or banded parenchyma. However, many species of this family mentioned in the Ethiopian flora (Puff 2003) can be excluded. This is the case for Filicium ‌decipiens ‌(Wight & Am.) and Zanha ‌golungensis ‌Hiern that differ from sample Twf 17854 by having procumbent cells in rays, wider intervessel pits (4-7 µm) and prismatic crystals present in ray cells. Cardiospermum ‌corindum L. has prismatic crystals in fibres and in ray cells, rays 4-10 seriate with two different sizes. Allophyllus ‌africanus ‌P. Beauv. and A. ‌macrobotrys ‌Gilg have exclusively uniseriate rays. Deinbollia ‌kilimandscharica ‌Taub and Lepisanthes ‌senegalensis ‌(Fuss. ex Poir.) Leenh have prismatic crystals in the ray cells. Haplocoelum ‌foliolosum ‌(Hiem) Bullock has procumbent cells (InsideWood 2004-onwards; Klaassen 1999). Among the Meliaceae, the closest match of the Omo fossil wood fragment appears to be with Entandrophragma. However, sample Twf 17854 is different from Twf 17913 that has wider rays. It may belong to a different species than Entandophragma sp. 2.

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 64 sect. 19 a; Unit A-1-1, 3.6 Ma; J. Heinzelin leg.; Twf 17872; Tervuren collection

Structures are better preserved in transversal section than in longitudinal section. Wood diffuse-porous. Growth rings absent. Vessels are solitary (45%) and in radial multiples of 2 (29 %), 3 (16 %), 4 (7 %), 5 (1%), 6 (1 %), clusters (2 %) (Fig. 8A, B). Vessels are rounded in outline or slightly oval, vessel wall thickness about 8-9µm. Mean tangential diameter of 90 µm, range 76-103 µm, 3-18 per mm²; perforation plates are exclusively simple, intervessel pits are alternate, polygonal, less than 4 µm. The poor quality of the conservation of the material does not allow us to conclude if intervessel-pits are vestured or not vestured (Fig. 8E). Vessel-ray-pits are not clearly distinct. Length of vessel cannot be evaluated. Tylose and gum deposits are not observed in vessels. Axial parenchyma is vasicentric with 1 or 2 rows of flattened cells, banded (3 to 10 cells with height 22 µm to 112 µm, wavy and sometimes confluent (anastomosed). Parenchyma strands 3-5 cells.

Rays are 1-2 (3) seriate, uniseriate and triseriate rays are rare, 16-18 per mm, heterocellular (Fig. 8D, F), composed of procumbent cells with 1-2 rows of square and upright cells (Fig. 8C, D). Ray height ranges from 81 µm to 690 µm (9-34 cells), ray width ranges 20-23 µm. Short rays are storied and high rays are sometimes irregularly storied. Sheath cells are visible on some rays. Uniseriate rays are composed of square and upright cells. Fibrer diameter is 13-27 µm, very thick-walled and pits are not observed, septate and non-septate fibres are observed. Crystals are distinct in ray cells that are procumbent and square and upright (Fig. 8D) and possibly present in unchambered parenchyma and fibres.

Twf 17854 and Twf 17872 differ only in the distribution of the axial parenchyma. In the case of Twf 17854, the parenchyma is irregular, or appears to be banded with patches of parenchyma that are wavy aliform and visually oblique. These two wood samples may represent two different species of Entandophragma, respectively called Entandophragma sp. 2 and Entandophragma sp. 3 (Table 1).

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 64; Unit A-1, 3.6 Ma; R. Bonnefille (73-11) leg.; Twf 18047; Tervuren collection.

The poor preserved structure of Twf 18047 in transversal section does not justify the previous attribution to Garcinia ‌(Dechamps 1983). Twf 18047 remains unidentifiable.

Ethiopia•Lower Omo Valley, Shungura Formation, locality 1 North; Unit B-10-2, 2.97 Ma; R. Bonnefille leg.; Nfw 001.

Nfw 001 is better preserved in transverse section than in longitudinal sections. The wood is diffuse-porous with growth rings only slightly marked by a reduction in fibres diameter (Fig. 9A). Vessels are solitary or in radial multiples of 2, 3 and exceptionally up to 5, there have rounded or oval outlines, and there are 5-10 per square millimeter. The mean vessel diameter is 90 µm (47-117 µm); vessels have medium thick walls. Length of vessel element is short; intervessel-pits are vestured and 6-7 µm wide (Fig. 9E), vessel-ray pits are indistinct. The axial parenchyma is vasicentric, confluent or winged aliform (Fig. 9A, B). The rays are 1-4 (5) seriate but occasionally 3 cells wide (Fig. 9C, D), consisting of procumbent, square, and upright cells that are evenly dispersed throughout the rays (Fig. 9F), range height is 102-291 µm (8-47 cells). There are approximately 10-12 rays per millimeter. Prismatic crystals are visible in the ray cells (Fig. 9E).

The features that characterize Nfw 001 are: vessels solitary or in radial multiples, simple perforation plates, minute and vestured vessel-pits, axial parenchyma vasicentric confluent and winged aliform; 1-4 (5) seriate rays with mixed procumbent, square and upright cells, prismatic crystals distinct in ray cells and druses in parenchyma. They are common in Combretaceae. In this family, ray cells with crystalliferous idioblasts occur in Combretum, Guiera, Finetia ‌(van Vliet 1979) and Terminalia. The first two genera have two sizes of vessels and the third has only uniseriate rays (InsideWood 2004-onwards). Terminalia with vessels of one size class, solitary or in low radial multiple, simple perforation plates, crowded and alternate vestured vessel pits, confluent parenchyma, rays heterocellular with idioblasts is the most probable attribution to the Shungura fossil wood sample illustrated in Fig. 9. We do not have information on the wood structure of all the 9 species recorded in Ethiopia (Vollensen 1995a). Information is missing for Terminalia ‌orbicularis, T. ‌spinosa ‌Engl., T. ‌prunioides ‌M.A.Lawson, T. ‌polycarpa ‌Engl. & Diels., T. ‌basilei ‌Chiov., T. ‌laxiflora ‌Engl. & Diels. and T. ‌schimperiana ‌Hochst. ex Engl. & Diels. However, we can exclude T. ‌macroptera ‌Guill. & Perr. and T. ‌brownii ‌Fresen having 1-3 seriate rays (InsideWood 2004-onwards).Terminalia ‌brevipes ‌Pamp., a common component of riparian forests in southern Ethiopia differs from the fossil wood sample. We have observed uniseriate rays in the tangential section of a modern specimen of T. ‌brevipes (P00950891) from of the Herbarium of the Paris Museum of Natural History.

Nfw 001 also shares some diagnostic features (rays with procumbent cells and square cells mixed in the rays with one row of upright cells, intervessels pits vestured, druses in chambered parenchyma and crystals in rays) described in Terminalioxylon ‌G.Schönfeld (InsideWood 2004-onwards). More than 60 fossil species have been described for this palaeobotanical taxon of worldwide distribution from the Eocene to the Miocene (Gregory et al. 2009). Among the species identified in Africa, we can exclude those that have thinner rays such as Terminalioxylontunesense ‌Dupéron-Laudoueneix (Dupéron-Laudoueneix 1973; Delteil-Desneux 1981), T. ‌crystallinum ‌Bamford (Bamford 2003), T. ‌mozambicense and T. edwardsii (Kräusel) Mädel-Angeliewa & Müller-Stoll, T. ‌primigenium ‌(Schenk) Mädel-Angeliewa & Müller-Stoll (El-Noamani 2020). T.edwardsii ‌(Kräusel) Mädel-Angeliewa & Müller-Stoll has uniseriate rays (El-Saadawi et al. 2014). T. ‌orangensis ‌Bamford (Bamford 2003). Other species from Ethiopia or Sudan, such as T. ‌edengense ‌Boureau (Boureau 1955),T. ‌cheidense ‌Fessler-Vrolant (Fessler-Vrolant 1980), T. ‌doubingeri ‌(Lemoigne 1978), T. ‌welkitii ‌(Lemoigne & Beauchamp 1972), T. ‌fezzanense ‌Boureau have uniseriate rays (Boureau 1958). T. ‌tunesense ‌Dupéron-Laudoueneix has 1-3 seriate rays (Fessler-Vrolant 1980).

The late Pliocene fossil wood from the Shungura Formation is better referred to the extant genus Terminalia than to any Terminaliaxylon paleobotanical species. Taking into account the state of preservation of the material, the identification involves some uncertainty; the material is designated Terminalia sp. 2. It differs from Terminalia sp. 1 (Twf 17918), collected from Member A, by its noticeably wider rays and a different distribution of axial parenchyma.

Ethiopia•Lower Omo Valley, Shungura Formation, Member B; Unit B-10, 2. Ma; Twf 17679; Tervuren collection.

Twf 17679 is poorly preserved, particularly in the tangential section and poor quality thin sections. Growth ring boundaries are not visible. The wood is diffuse-porous, vessels occurring exclusively as solitary or in radial multiple of 2 or (3), oval in shape, 5-8 per mm², gum deposits distinct in vessels. Axial parenchyma is vasicentric and banded. Vessel elements, vessel pits and rays are not visible on longitudinal sections, and no prismatic crystals observed in wood tissue.

Twf 17679 was originally identified as Ficus sp. (Dechamps 1983). However, due to the lack of diagnostic characters about vessel elements, vessel pits, and rays, prismatic crystals not observed in the longitudinal planes, the identification to Ficus does not seem to be well founded. Twf 17679 remained unidentified (Table 1).

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 782 sect. 18; Member B, Unit B-12, 2.95 Ma; J. Heinzelin leg.; Twf 17609; Tervuren collection.

Twf 17609 exhibits good preservation. The wood is diffuse-porous, without distinct growth ring boundaries. Vessels are exclusively solitary (Fig. 10A), round in shape with an angular outline, 35-40 per mm², mean vessel diameter is 40 µm (range between 14-58 µm); vessels are thick walled 4-5 µm. Gum deposits are distinct in vessels (Fig. 10B). Vessel elements measure 350-650 µm in length, intervessel-pits measure 3-4 µm wide and are alternate (Fig. 10F), vessel-ray pits are not visible. Axial parenchyma is extremely rare (Fig. 10B). Rays are 1-2 seriate (occasionally 3) cells wide and 20-25 per mm, composed of procumbent, square and upright cells mixed throughout the rays (Fig. 10C-E), mean height is 1500 µm, range 50-2000 µm (53-70 cells), ray width range is 12-15 µm. Alternating bands of medium to thick-walled septate fibres and thinner-walled non-septate fibres have diameters between 9-22 µm (Fig. 10A, B). Prismatic crystals are present in ray cells (Fig. 10C-E).

The anatomical features described, such as diffuse-porous wood, solitary vessels, simple perforation plates, bands of fibres resembling parenchyma that alternate with ordinary fibers, both non-septate and septate ones, absent or scanty axial parenchyma, heterocellular rays 1-(3) seriate, axial parenchyma absent or scanty paratracheal are typical of the Celastraceae. These diagnostic characters are not found in the Ebenaceae and do not support the previous identification to Diospyros ‌(Dechamps 1983).

In Ethiopia, the family Celastraceae is represented by four genera (Catha,Elaeodendron,Maytenus and Mystroxylon) comprising a total of seven species. Catha ‌edulis ‌(Vahl) End Forssk. ex Endl. has no crystal inclusions in ray cells (InsideWood 2004-onwards). Elaeodendron ‌buchananii ‌(Loes) Loes has scalariform perforations plates (InsideWood 2004-onwards). We exclude Mystroxylon ‌aethiopicum ‌(Thunb.) Loes (syn.: Cassineaethiopica ‌Thunb.) which exhibits banded parenchyma, composed rays of procumbent cells with 2-4 rows of upright cells (InsideWood 2004-onwards), anatomical features not observed in the fossil sample. Twf 17609 shows close affinity to Maytenus ‌Molina and is attributed to Maytenus sp. 1.

In Ethiopia there are 12 species of Maytenus (Demissew 1985, 1989; Robson & Demissev 1989. Among them M. ‌senegal­ensis ‌(Lam.) Exell is the only species common in deciduous woodland, open dry scrub or river margins that shows similarities with Twf 17609 but exhibits a higher proportion of 3 seriate rays (InsideWood 2004-onwards).

Few paleobotanical fossil wood have been attributed to the Celastraceae. Celastrinoxylon ‌celastroides ‌(Schenk) Kräusel was recorded in Cretaceous deposits of Egypt (Kräusel 1939) and in Eocene-Paleocene strata from Harar in Ethiopia (Beauchamp & Lemoigne 1973). These paleobotanical species differ from the Shungura specimen in having wider vessel pits and banded parenchyma. Therefore, Twf 17609 is attributed to Maytenus sp. 1.

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 180 sect. 10; Unit C-5; 2.62 Ma; J. Heinzelin leg.; Twf 17839; Tervuren collection.

Twf 17839 keeps the central zone of the central cylinder, but it is poorly preserved with abundant fungal hyphae (Fig. 11A). Fibrovascular bundles (fvb) are more or less crowded and mainly regular in distribution (average size 900-950 µm, average frequency 16 fvb per cm2). Sclerenchyma cap is reniform with auricular lobes rounded, median sinus deep rounded (Fig. 11B, C). Fibrous bundles are absent. The sclerenchyma cap has the r/tg mean diameters (919/463 µm). The sclerenchyma cap is made by fibrous cells having a round cross-section of 31 µm (range 13-48 µm) mean diameter; they are thick-walled (Fig. 11B). The metaxylem is badly preserved, most often compressed with a single large metaxylem vessel (90-225 µm). The phloem, usually protected under the median sinus, is not distinct. Ground tissue is compact, composed of small round thin-walled cells, tabular parenchyma and radiate parenchyma are absent or indistinct. Longitudinal thin section is missing.

In cross section, the diagnostic xylotomical features of Twf 17839 are fibrovascular bundles with reniform sclerenchyma caps with rounded auricular lobes, badly preserved vascular part with few details on the compressed or destroyed phloem and one large metaxylem vessel. The ground tissue consists of rounded, densely packed cells.

Twf 17839 mostly resembles Borassus L. from the Arecaceae family (Tomlinson 1961; Dransfield et al. 2005; Tomlinson et al. 2011; Thomas & de Franceschi 2013). Others Ethiopian Arecaceae such as Phoenix and Hyphaene have been described with two metaxylem vessels (Tomlinson 1961). We exclude also Draceana Mand. among the Dracenoid, clade of Asparagaceae ‌(APG 2016). Indeed, this genus has scattered vascular bundles in parenchyma. In transverse section, around the primary tissue at the center of the stem, the stem anatomy shows a secondary tissue that contained crowded amphivasal vascular bundles. In addition, the parenchymal cells in secondary tissue were radially and orderly arranged around amphivasal bundles in a strip shape.

Twf 17839 presents the typical structure of the stem of a palm tree, a member of the Arecaceae ‌Berchtold & Presl. This structure was well defined in the original diagnosis of the palaeobotanical Palmoxylon ‌Schenk. Fossil remains of Arecaceae in Africa are documented from the Aptian to the Pleistocene including fruits, leaves, petioles, pollen, stems and phytoliths (Pan et al. 2006; El- Saadawi et al. 2002, 2004; Kamal El-Din et al. 2013). The paleobotanical genus Palmoxylon ‌Schenk includes 28 species described from Africa (Chiarugi 1929a, b; Louvet 1971; Delteil-Desneux & Koeniguer 1974; Dechamps 1983; El-Saadawi et al. 2002, 2004, 2014; Nour-El-Deen et al. 2018). In Ethiopia, two specimens from the Upper Omo valley have been identified as Palmoxylon ‌ethiopicum ‌(Lemoigne 1978). These specimens differ from Twf 17839 by having two large vessels and tabular parenchyma. Our specimen bears some resemblance with P. ‌aschersonii ‌Schenk notably, regarding the shape of sclerenchyma cap of fvb, and the parenchymal ground-tissue aspect. P. ‌aschersonii ‌Schenck described again from Paleogene/Neogene deposits in Algeria and Miocene of Libya was compared with the extant species Borassus ‌aethiopum ‌Mart. (Boureau 1947. In conclusion, Twf 17839 is attributed to Borassus sp.

Ethiopia•Shungura Formation, Lower Omo Valley, locality P 811 sect.4, Unit C-5; 2.62 Ma; Jean de Heinzelin leg.; Twf 17748; Tervuren collection.

Twf 17748 is poorly preserved, with no fungal structures observed in any thin sections. It exhibits a diffuse, porous feature and lacks discernible growth rings. Vessels are arranged in radial lines of 2-3 pores, clusters are present (Fig. 12A). The vessel mean tangential diameter is 120 µm (range 115-138 µm), there are 2-5 vessels per mm². The mean vessel element lenght is 220 µm (range 100-250 µm). Intervessel-pits and vessel-ray-pits are indistinct. Distinct tyloses are visible within the vessel lumens (Fig. 12B, C). Axial parenchyma is vasicentric with one or two rows of cells and banded, usually consisting of 5-6 cells wide (Fig. 12C). Parenchyma strands have fusiform cells that are storied (Fig. 12E). Rays are 1-6 seriate, 5-6 per mm, and can reach a height of 1mm (Fig. 12E-G), mean ray width is 80 µm (range is 75-100 µm). They are composed of procumbent cells that are accompanied by a row of square or upright cells (Fig. 12D). Sheath cells are noticeable (Fig. 12E). Fibers are medium to thick walled, storied and probably non-septate. Crystal inclusions are distinct in ray cells.

Wide vessels solitary or in radial groups, high heterocellular pluriseriate rays, paratracheal parenchyma reticulate and in wide bands and partly storied cells, short vessel elements and sheath cells shows similarities with Boraginaceae and more specifically in Cordia ‌(Dechamps 1983). Of the six Ethiopian species (Hedberg et al. 2006), Cordia ‌africana ‌Lam. shows similar characters, although we have no anatomical description for the other five species C. ‌sinensis ‌Lam.,C. ‌quercifolia ‌Klotzsch,C. ‌monoica ‌Roxb.,C. ‌ellenbeckii ‌Gurke,C. ‌crenata ‌Del. (Riedl & Edwards 2006). Therefore Twf 17748 is attributed to Cordia sp. 1 with a special reference to C. ‌africana.

A palaeobotanical species Cordioxylon ‌barthelii ‌Süss has been described from the southwestern Sahara in Egypt (Paleogene), but it differs from the Omo specimen by its vasicentric axial parenchyma (Süss 1987). In conclusion, due to the limited number of comparative references to extant species, Twf 17748 is attributed to Cordia sp. 1

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 59 sect. 4, Member C-5; 2.62 Ma; Jean de Heinzelin leg.; Twf 17610; Tervuren collection.

The preservation of Twf 17610 is poor, and certain micro-anatomical features are indistinct. No fungi are visible in thin sections, the wood underwent alteration prior to its fossilisation. The wood is diffuse-porous, growth rings are absent; vessels are arranged in low radial lines of 1-3 pores, primarily singular, and few clusters are present (Fig. 13A, B). Vessel frequency is 1-4 per mm². The mean vessel element is 245 µm, and the tangential diameter of vessels ranges from 140 µm to 345 µm. Intervessels and vessel-ray pits are indistinct in thin sections. Tylosis is observed in vessels’ lumina (Fig. 13B). Axial parenchyma is predominantly vasicentric, with a banding pattern, mostly 8-10 cells high or seemingly banded (Fig. 13A, B). Parenchyma strands are irregularly storied and consist of fusiform or 5-8 cells. Rays are 1-6 seriate composed of procumbent cells with 1-2 rows of square and upright cells, more than 1mm high (range 595-1299 µm), mean ray width 80 µm (range 43-130 µm) (Fig. 37C), they are 4 per mm. Sheath cells are present. The fibres are medium to thick walled, storied (Fig. 37D) and most likely not septate. Ray cells contain clear crystal inclusions, idioblast (Fig. 37E, F).

Twf 17610 shows wide solitary vessels or radial groupings, high heterocellular pluriseriate rays, paratracheal parenchyma that is reticulate in wide bands and partly composed of storied cells, short vessel elements, sheath cells, indicating similarities with Boraginaceae and more specifically with Cordia in accordance with Dechamps’ diagnosis.

Twf 17610 is related to Twf 17748, described above as Cordia sp. 1 (Table 1; Fig. 12). However, it differs by having larger vessels and therefore is designated as Cordia sp. 2. (Fig. 13; Table 1).

Ethiopia•Lower Omo Valley, Shungura Formation, locality L 46-36 sect. 4; Unit C-5, 2.62 Ma; Jean de Heinzelin leg.; Twf 17812; Tervuren collection.

Twf 17812 shows moderate preservation, devoid of any fungal presence. It belongs to the diffuse-porous type, with either indistinct or entirely absent growth rings. The vessels are mostly solitary (61%), with some in radial multiples of 2 (28%) and 3 (11%) (Fig. 14A). Their mean tangential diameter is 185 µm, ranging from 138-230 µm, and there are 1-4 per square millimeter. Intervessel-pits are 7-8 µm wide, sometimes coalescent, crowded alternate, and have an angular outline (Fig. 14A). Vessel-ray-pits are similar to intervessels-pits. The axial parenchyma is vasicentric, around 1-5 cells wide, aliform, and sometimes confluent around 3 to 4 vessels (Fig. 14A). Parenchyma strands are made of 3-4 to 5-8 cells. The rays range from 1-10 cells wide (Fig. 14C, D), mean ray height is 400 µm (range is 268-618 µm) and mean rays width is 90 µm (range 70-100 µm) they are composed of procumbent cells containing one or two rows of square and upright cells (Fig. 14D, E). Uniseriate rays are entirely formed of upright cells, totaling 7-8 per mm. Sheath cells are clearly distinguishable. Fibres have thin walls and are not partitioned. Prismatic crystals are present in both the ray cells and chambered parenchyma cells (Fig. 14F-G).

The observed anatomical features: diffuse-porous wood, vasicentric to confluent axial parenchyma, prismatic crystal in square or upright cells, wide multiseriate rays and sheath cells, resemble more closely Celtis cf. C. ‌integrifolia than Kigelia ‌africana to which it was erroneously attributed (Dechamps 1983), prismatic crystals are absent in Kigelia and intervessel pits are bigger that those of Twf 17812.

To the best of our knowledge, no fossil Celtis wood are known from Africa. Three generic names – Celtisoxylon Triverdi, Celtixylon ‌Greguss and Celtoxylon Wurzinger – created for fossil woods resembling Celtis were not properly diagnosed (Gregory et al. 2009). Celtisoxylon was applied to a wood from Deccan inter-trappean beds of India, but only mentioned in an abstract without diagnosis or designation of holotype, Celtixylon was never formally diagnosed and Celtoxylon, mentioned in a Ph’D thesis, was never formally published. Woods thought to have affinities with Celtis have been reported from the Miocene Europe, and Asia (Selmeier 1989, 2015), and North America (Wheeler & Manchester 2021). Twf 17812 attributed to Celtis thus represents the first documented occurrence of this genus in Africa.

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 508; Middle Member C, 2.62 Ma; Jean de Heinzelin leg.; Twf 17611; Tervuren collection.

The specimen displays moderate preservation in both transverse and tangential sections, and better preservation in the radial section. Fungi are not present. Wood diffuse-porous is without growth rings. Vessels are solitary (63%) and in radial multiples of 2 (29%), 3 (7%), 4 (0.5%) and 5 (0.5%). Mean tangential diameter of 86 µm (range 34-103µm), 6-20 vessels per mm² (Fig. 15A, B). Perforation plates are exclusively simple; intervessel-pits are crowded alternate with areoles, 5-6 µm wide and vestured (Fig. 15E); vessel-ray pits are similar to vessel-pits; mean vessel element length short 126-137 µm, gum-like deposits are present in vessels. Axial parenchyma paratracheal, confluent to irregularly, seemingly sinuous banded (2-4 cells), sometimes up to 8 cells wide, in strands of cells 2-3 (2-4 cells). Rays are (1)-2-3-seriate (Fig. 14C, D), heterocellular composed of procumbent cells with square and upright cells or exclusively composed of square and upright cells (Fig. 15F), 6-9 per mm, mean height of the rays is 290 µm (range 172-483 µm), and width 22-80 µm. Fibers are thick to mostly very thick walled with distinct septae. Possible occasional strands of crystalliferous axial parenchyma, one rhomboidal crystal per chamber, 8 chambers per strand, crystal are distinct in ray cells too and sometimes in enlarged cells (Fig. 15D).

The combination of vessels solitary and in radial multiple, simple perforation plates, narrow (100 µm mean tangential diameter) vessels, vasicentric, aliform, and banded or seemingly banded, narrow rays, chambered crystalliferous parenchyma occurs in woods of Combretaceae and Fabaceae. Vessel-pits are usually smaller in some Combretaceae. The affinities of Twf 17611 fossil wood are more likely with the genus Terminalia. Among the African Terminalia with sinuous, seemingly banded parenchyma, broad bands in long tangential lines are found in T. ‌macroptera ‌(Neumann et al. 2001). Among african species T. ‌avicennioides ‌Guill. & Perr. and T. ‌glaucescens ‌Planch. ex Benth have 1-3 seriate rays but no crystals in ray cells. T. ‌boivinii ‌Tul and T. ‌macroptera are described with axial parenchyma seemingly banded mostly 1-3 cells wide, often discontinuous. T. ‌macroptera showing rather confluent to banded pattern (Neumann et al. 2001) is the most similar species to our Pliocene Shungura sample Twf 17611.

Among the twelve palaeobotanical Terminalioxylon species of Africa that we have already mentionned in Member A, Terminalioxylon ‌welkitii ‌Lemoigne (Lemoigne & Beauchamp 1972) and Terminalioxylon sp. Lemoigne, Beauchamp & Samuel (Lemoigne et al. 1974) have been identified from the Cenozoic in Ethiopia. These species exhibit uniseriate rays with procumbent cells. T. ‌doubingeri ‌Lemoigne (Miocene, Upper Omo Valley) displays 1-3 seriate homocellular rays, terminal parenchyma and septate fibres (Lemoigne 1978). T. ‌endengense ‌Boureau (Eocene, northern Sahara) displays abundant parenchyma, fibers are not septate and rays are uniseriate (Boureau 1955). T. ‌primigenium ‌Madel Angeliewa & Muller-Stoll, 1972T. ‌qeinitzii, and T. ‌intermedium ‌Madel-Angeliewa & Muller-Stoll, 1973 (late Cretaceous-Eocene, Sudan) display mostly small vessels, usually in multiples, and vasicentric parenchyma. T. ‌edwardsii, described by Madel Angeliewa & Muller-Stoll in 1973 from the Oligocene to Miocene in Egypt, exhibits a high abundance of parenchyma and longer rays. Among other Terminalioxylon described with 1-3 seriate rays, T. ‌orangensis ‌Bamford has scanty axial parenchyma,T.crystallinum ‌Bamford has vasicentric parenchyma (Bamford 2003), T.doubingeri ‌Lemoigne has vasicentric, confluent or seemingly banded parenchyma (Lemoigne 1978), T. ‌tunesense ‌Dupéron-Laudoueneix has vasicentric parenchyma (Fessler-Vrolant 1978). The Omo fossil specimen does not correspond to any of these paleobotanical species. Unlike Twf 17918, described before from Member A, dated 3.6 Ma and that was attributed to Terminalia sp., the wood sample Twf 17611 from Member C, dated 2.62 Ma, is more precisely attributed to the species T. cf. macrocarpa.

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 106 sect. 4; Unit C-5, 2.62 Ma; Jean de Heinzelin leg.; Twf 17683; Tervuren collection.

Twf 17683 exhibits well-preserved micro-anatomical structures, without any visible presence of fungi. The wood is diffuse-porous; growth rings are absent (Fig. 16A, B). Vessels are solitary (38%) or in radial lines of 2 (42%), 3 (12 %) and 4-5 (8%). The frequency is 10-20 vessels per mm². Mean tangential diameter is 80 µm (range 57-90 µm). Vessel element length is 184-621 µm; perforation plates are simple. Intervessel-pits, poorly preserved are alternate, 3-4 µm wide and not vestured (Fig. 16E); gum is distinct in vessels. Axial parenchyma is scanty to vasicentric with 1-2 rows of cells, and diffuse-in-aggregates (Fig. 16B).

Rays are uniseriate and reach heights ranging from 161 to 520 µm. They are numerous (26-28 per mm) and are composed of square and upright cells mixed throughout the body of the rays (Fig. 16C, D). Fibres are medium to thick walled and septate. Prismatic crystals are distinct in ray cells (Fig. D, F-G).

Vessels solitary or in radial multiple, rare parenchyma with irregular narrow bands, and uniseriate heterocellular rays with enlarged crystalliferous cells occur in woods of some members of the Annonaceae, Apocynaceae, Balanitaceae, Ebenaceae, Euphorbiaceae, Clusiaceae, Malvaceaesensu lato (including Tiliaceae), and Sapotaceae (InsideWood database 2004-onwards). Among the Ebenaceae, we exclude Euclea for which two montane species, Euclea ‌racemosa Murr. (1774) subsp. schimperi (A.D C.) F. White and E. ‌divinorum ‌Hiern have uniseriate rays (InsideWood database 2004-onwards). Twf 17683 shows characters found in Diospyros. Among the three Diospyros species known in the Ethiopian flora (Friis & White 2005), D. ‌scabra ‌(Chiov.) Cufod. is not described in databases. D. ‌abyssinica (Hiern) F. White possesses uniseriate rays and has both diffuse and diffuse-in-aggregates parenchyma, as well as reticulate axial parenchyma (InsideWood database 2004-onwards; Metcalfe & Chalk 1950). But its vessels are generally smaller than those of Twf 17683. In conclusion, this sample shows similarities with D. ‌mespiliformis that has diffuse-in-aggregates parenchyma.

Among the palaeobotanical species from Libya (Cretaceous) and related to the Ebenaceae, Ebenoxylon ‌ebenoides ‌Kräusel (Schenk) Edwards (synonym of Jordania ‌ebenoides ‌Schenk) shows solitary vessels and scalariform perforation plates but its attribution to the Ebenaceae is probably an erroneous identification (A. Pan in lettris). Nevertheless, it differs from Twf 17683. E. ‌aegyptiacum ‌Kräusel from the Oligocene of Egypt and E. ‌tunetanum ‌(Fliche) Edwards (synonym of Jordania tunetana Fliche) from the Oligocene of Tunisia show some similarities to the Omo fossil. In contrast, E. ‌saharicum ‌Süss from the Paleogene of Egypt displays larger vessel diameters (150-215 µm) and rays are 1-3 seriate (Süss 1987).

Diospyros sp. has been identified in Pleistocene (1.95 Ma) deposits of the Koobi Fora Formation, Lake Turkana Basin in Kenya (Bamford 2011). This specimen is characterized by wider vessels (164 µm) and short radial multiple, all features that distinguish it from Twf 17683, identified as Diospyroscf. mespiliformis.

Ethiopia•Lower Omo Valley, Shungura Formation, locality L 642-8 sect. 8; Unit C-6, 2.61Ma; American Staff leg.; Twf 17713; Tervuren collection.

Twf 17713 displays moderate preservation, with no visible presence of fungi (Fig. 17A). It exhibits characteristics of diffuse-porous wood, with either absent or indistinct growth rings. Vessels are solitary (31%) and in radial multiples of two (36%), 3 (21%), 4 (11%) and 5 (1%). They are 20-35 per mm², round to oval in outline (Fig. A, B). Mean tangential diameter is 45 µm (range 21.5-66 µm). Perforation plates are simple (Fig. 17C); intervessel-pits are alternate, 3-4 µm wide and not vestured (Fig. 17E). Vessel-ray pits are indistinct. Mean vessel element height is short (range185-350 µm) Fibres are irregular thin-medium walled (4 µm), non-septate observed. Gum is distinct in vessel lumina (Fig. A).

Not well preserved on the transverse section, it is particularly difficult to differentiate parenchyma from fibres. Axial parenchyma seems vasicentric, with one or two rows of flattened cells, diffuse and probably diffuse in-aggregates. Parenchyma strands are 3-4 cells. Rays are uniseriate, locally biseriate, they are 12-14 per mm (Fig. 17C, D), square and upright cells are mixed in the rays (Fig. 17F), mean ray height is 320 µm (range 165-520 µm (7-28 cells) mean ray height is 320 µm (range 165-520 µm (7-28 cells) mean ray width is 30 µm (range 15-34 µm), Crystals are visible in ray cells and in parenchyma.

The wood shows the anatomical features of Meliaceae characterized by minute and not vestured intervessel-pits, rare axial parenchyma, septate fibres and heterocellular rays. Among the Meliaceae, the combinations of crystals in marginal cells or parenchyma, homocellular or heterocellular rays and septate or non-septate fibres are used to distinguish subfamilies (Kribs 1930). Twf 17713 can be attributed to the Melioideae subfamily (Muellner et al. 2003) with characters found in Trichilia. The wood anatomy of Trichilia and Pseudobersama differs very little, except in regard with the vessels frequencies and grouping (Gasson & Cheek 1992; Inside Wood database 2004-onwards). The secondary xylem of Pseudobersama can be distinguished from the African species of Trichilia by the very large numbers (80-100 per mm²) of small, vessels (20-40 µm) arranged in radial rows of 2-5 and the rather sparse aliform and confluent parenchyma. African species of Trichilia have up to 30 vessels per mm² with a tangential diameter from 40-220 µm. In Pseudobersama the number of solitary vessels is greater, rays are exclusively uniseriate, inclusions are absent in ray cells. Trichilia ‌dregeana and T. ‌emetica have larger vessels (100-200 µm) than Twf 17713. T. ‌prieureana have exclusively uniseriate ray composed of procumbent cells with 1-2 rows of square and upright cells

Of the two palaeobotanical species linked to Trichilia,Paratrichilioxylon ‌grambastii ‌Lemoigne (Lemoigne 1978), from the Upper Omo Valley possesses three seriate rays,P.russelli ‌Koeniguer from the Paleocene in Niger (Koeniguer et al. 1971) has axial parenchyma in narrow bands or lines up to three cells wide. They strongly differ from Twf 17713, which is likely attributable to Trichilia sp.

Ethiopia•Lower Omo Valley, Shungura Formation, locality L 448 sect. 11; Unit C-8, 2.57 Ma; American Staff leg.; Twf 17805, Twf 17808; Tervuren. collection.

Twf 17805 and Twf 17808 closely resemble Twf 17609 already described in Member B-12. Sharing the same characteristics, we attribute all of these samples to Maytenus sp. 1

Ethiopia•Lower Omo Valley, Shungura Formation, locality L 447-1 sect. 11; Member C-8, 2.57 Ma; American Staff leg.; Twf 17788; Tervuren collection.

Twf 17788 is well preserved showing fibro-vascular bundles irregular in distribution, having developed reniform sclerenchyma caps, with a small median sinus, with rounded auricular lobes, frequency 30-35 per mm². Xylem with two round vessels and compact parenchymal ground tissue (Fig. 11E F). The fibrous bundles are missing. The sclerenchyma cap is 400-470 µm in height and 500-600 µm wide (Fig. 11G). The phloem is indistinct (Fig. 11H). The xylem appears in cross-section with 2 round large vessels of 100-150 µm diameters in cross section. The ground parenchyma is composed of round cells, tabular parenchyma is present and radiating parenchyma is absent. Longitudinal section being absent, the vertical walls of the metaxylem vessels could not be observed.

In cross section, Twf 17788 presents a monocotyledonous fascicular structure typical for the stem of palm tree of the Arecaceae ‌Bercht. & Presl. The general organisation of the central cylinder stem pattern (ex-von Mohl’s classification) of Corypha-type and Mauritia-type shows reniforma fibrovascular bundles with an excluded vascular part and two large vessels elements with little paravascular parenchyma in Twf 17788 the phloem is not partitioned. The ground parenchyma is compact, made of spheroid cells. Tabular parenchyma is present (Fig. 11H). No fibrous bundles were observed in the ground parenchyma. These features are similar to the Calamoideae-Lepidocaryeae and more specifically to the genus Raphia.

The fossil corresponds to Palmoxylon that generally defines “wood of Palm” (Schenk 1883). Twf 17788 is similar to Palmoxylon ‌rewahense ‌Sahni, and Palmoxylon ‌libycum described in the early Miocene of Qaret El-Raml, from Egypt (Lemoigne 1978).

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 755 sect. 24; Unit C-8, 2.57 Ma; Jean de Heinzelin leg.; Twf 17638; Tervuren collection.

Twf 17638 is poorly preserved diffuse-porous, with indistinct growth rings Vessels are frequently solitary (87%), and in radial multiple of 2 (%), 3 (%), 8-11 vessels per mm² (Fig. 19A, B). Very few vessel clusters were seen (0.5%). Mean vessel tangential diameter is 150 µm (range 58 µm-254 µm). Perforation plates are simple horizontal to slightly oblique. Intervessel pits are polygonal, relatively dense, alternate, and 7-8 µm in size, They appear vestured (Fig. 19E). Mean vessel length is 350 µm (range 166 µm to 676 µm). Vessel-ray pits are indistinct. Gum is visible in the vessels (Fig. 19A).

Axial parenchyma is paratracheal, vasicentric, aliform and sometimes confluent (Fig. 19A, B).

Rays are 1-4 (5) seriate, 5-6 per mm, uniseriate are rare, homocellular composed of procumbent cells, (Fig. 18C, D, F). Mean ray length is 234 µm (range 169-676 µm), mean ray width is 25 µm (range 13-30 µm). Fibers are septate. Strands of crystalliferous axial parenchyma, single one rhomboidal crystals are distinct in fibers and in parenchyma strands, there are 10-24 chambers per strand (Fig. 19G).

The combination of the characters: vessels solitary (87%), vestured intervessel-pits, axial parenchyma paratracheal vasicentric, aliform and confluent, 1-5 seriate rays with only procumbent cells, prismatic crystals in chambered parenchyma and septate fibres are features found in the Fabaceae, especially the Mimosoideae (now included in the Caesalpinioideae subfamily by the Legume Phylogenetic Working Group) (LPWG 2017). Storied rays, which would have placed Twf 17638 closer to the Faboideae or some Caesalpiniaceae are absent (Metcalfe & Chalk 1950; Müller-Stoll & Mädel 1967). In Ethiopia, trees of the Mimosoideae include six distinct genera: Dichrostachys, Albizia, Entada, Prosopis, Mimosa and Acacia ‌(Thulin 2003). With septate fibres, Twf 17638 is similar to Albizia. It was previously attributed to A. ‌antunesiana(Deschamps 1983). However, it differs from A. ‌antunesiana as described in the literature (InsideWood 2004-onwards), notably in its higher vessel density per mm², larger vessels and pits, and more abundant parenchyma. Twf 17638 also differs from other Ethiopian species for which anatomical data are currently available. Given the absence of anatomical data for many other Ethiopian and East African species, a confident species-level identification is not possible; Twf 17638 is therefore conservatively assigned to Albizia sp. It may also represent a distinct species from the one attributed to the fossil wood identified in the 5.8 Ma old deposits at Middle Awash that has bigger vessels and shorter rays (Jolly-Saad et al. 2012). Therefore, our revision of Twf 17638 leads to an identification as Albizia sp. 1, excluding A. ‌autunesiana ‌(Dechamps 1983).

Among fossil wood reported to Albizia in Africa, few specimens have been related to Albizia, one from Cameroon, Ingoxylon ‌albizzoides ‌(Dupéron-Laudoueneix 1991) has bigger vessels and shorter rays than the Omo fossil specimen. A. cf. gummifera.

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 424 sect. 15; Unit C-9, 2.56 Ma; Jean de Heinzelin leg.; Twf 17730; Tervuren collection.

Twf 17730 is poorly preserved. Wood diffuse-porous, growth rings are absent. Vessels are round or oval in shape, solitary or in short radial multiple 2-3 with mean tangential diameter of 90 µm (range 95-81 µm), 2-4 vessels per sq. mm, vessels are thin-walled. (Fig. 20A, B). Gum deposits are distinct in vessel lumina, tylosis is not observed. Vessel element length is 200 µm (range 80-270 µm), perforation plates are simple and horizontal. Intervessel pits are opposite and vestured 7-8 µm wide (Fig. 20F), vessel-ray pits are indistinct. Axial parenchyma is vasicentric to confluent (Fig. 20B). Parenchyma strands are 2-4 cells. Rays are 1-3 (4) seriate, heterocellular, 11-12 or > 12 per mm. Mean ray height is 235 µm range 72-460 µm 39 µm (range 26-48) (Fig. 20C, D-F). Fibres are wide and they are septate. Inclusions are distinct in chambered parenchyma and in ray cells.

Twf 17730 was initially identified as Kigelia ‌africana from the Bignoniaceae ‌(Dechamps 1983). However, upon closer examination, its characteristics strongly differ from those of the Bignoniaceae, notably its vestured vessel-pits, crystals in ray cells, in parenchyma cells and septate fibers. Other traits such as medium-sized vessels, alternate and vestured vessel-pits, vasicentric to confluent axial parenchyma, 1-4 seriate rays comprising procumbent cells, and chambered crystalliferous axial parenchyma suggest affinities with Combretaceae or Fabaceae with no more precision because of poor preservation of this sample.

Ethiopia•Lower Omo Valley, Shungura Formation, locality L 553-2 sect. 9; Member D-1, 2.53 Ma; J. de Heinzelin leg; Twf 17613; Tervuren collection.

Twf 17613 is poorly preserved, abundant fungal spores are visible in vessel lumina. Wood is diffuse-porous and growth boundaries are indistinct. Vessels are solitary (71%) and in radial groups of 2-3 (5), few clusters are present (Fig. 21A). Mean vessel diameter is 85 µm (range 34-138 µm), vessel wall is thick (11 µm thickness), there are 1-8 vessels per mm². Perforation plates are exclusively simple; intervessel-pits are crowded alternate, 5-6 µm and seem vestured (Fig. 21F), vessel-ray pits are indistinct. Gum is not visible in vessels. Parenchyma is abundant, vasicentric and banded; bands are wavy, 2 cells wide (34 µm) up to 20 cells (345 µm) (Fig. 21A, B); parenchyma strands are fusiform and storied. Rays are 1-4-(5) seriate with short uniseriate marginal parts, heterocellular and composed of procumbent cells and upright cells (Fig. 21B, C). Uniseriate rays are short (2-5 cells high) and seem partially storied (Fig. 21), 6-7 per mm, mean height range is 600 µm (70-977) (4-43 cells), mean width range is 11 to 90 µm. Strands of crystalliferous axial parenchyma show one rhomboidal crystal per chamber and crystals are visible in upright cells of rays.

The combination of solitary vessels and in radial multiples, simple perforation plates, axial parenchyma vasicentric, confluent and aliform, crystalliferous parenchyma with chambers, heterocellular rays 1-4 seriate occurs in the woods of Fabaceae. Crystals in Caesalpinioideae are primarily found in axial parenchyma with chambers, often in ray cells and occasionally in fibers with chambers (Gasson et al. 2004). Twf 17613 was initially attributed to Platysepalum ‌chevalieri ‌Harms (Dechamps 1983). A detailed description of two species, namely P. ‌chevalieri ‌Harms and P. ‌violaceum ‌Baker (Lebacq 1955-1963), shows that these two species, in contrast to other Millettieae, exhibit less pronounced banding, axial parenchyma, diffuse and scanty paratracheal, aliform, confluent, and that parenchyma strands are fusiform, 2 or 2-4 cells per strand. The rays typically include 5-6 cells in width and up to 50 cells in height, with only the shortest being storied. The intervessel-pits are wide, 8-13 µm. The specimen Twf 17613 displays distinct differences from P. ‌chevalieri. Specifically, the rays are heterocellular and thinner (1-4 seriate), while the parenchyma strands are composed of 3-4 cells. Unfortunately, no xylo anatomical data are available for P. ‌inopinatum, a species found in East Africa (Gillett et al. 1971). Among the Fabaceae family, the species that possess heterocellular rays and prismatic crystals in both procumbent and upright cells are Mundulea,Chadsia, ‌ Craiba (Millettieae) and Bauhinia. However, it should be noted that these species have only 1 to 3 seriate rays (Gasson et al. 2004). Among the taxa of the Detarioideae (Fabaceae), Cynometra is characterized by hetero­cellular rays and prismatic crystals found in the ray cells. While these characteristics are also present in the Shungura specimen, most members of the Cynometra species described in data bases have thin rays that are either uniseriate or triseriate. Extant trees or shrubs displaying traits similar to our fossil belong to Baphia (subfamily Faboideae, tribe Baphieae). Similarities exist with the western African species Baphia ‌bequaertii ‌De Wild. However, B. ‌bequaertii differs with narrower axial banded parenchyma and 2-4 cells per parenchyma strands. Baphia ‌leptobotrys ‌Harms is 1-3 seriate; Baphia ‌nitida ‌Lodd. is the most similar species. Unfortunately, we do not have anatomical data for B. abyssinica ‌Brummitt, the only species recorded in Ethiopia (Thulin 2003).

Among morphotypes,Baphioxylon ‌abyssinica ‌Lemoigne from the Miocene of Upper Omo Valley differs from the Shungura fossil specimen with no crystal inclusions and distinct tylose in vessels (Lemoigne 1978), Baphioxylon ‌dechampsii ‌Lakhanpal & Prakash from early Miocene of Lake Albert has thinner rays (Lakhanpal & Prakash 1970). In conclusion, we attribute Twf 17613 to the extant genus Baphia without any specific attribution.

Ethiopia•Lower Omo Valley, Shungura Formation, locality L 553-1 sect. 9 Member D-1, 2.53 Ma; Jean de Heinzelin leg.; Twf 17804; Tervuren collection.

Twf 17804 is diffuse-porous and growth rings are indistinct. Vessels are frequently solitary (87%), and in radial multiple of 2 (2%) or 3 (1%) with very few clusters, 10-15 vessels per mm² (Fig. 22A, B), round to elliptic in cross section, very often deformed. Mean tangential diameter 80 µm (range 40-90 µm) (Fig. 22A, B). Vessel elements are short 104 µm (60-192 µm), perforation plate simple horizontal to slightly oblique, intervessel-pits, alternate, possibly vestured and 4-7 µm wide. Vessel-ray pits are horizontal (scalariform, gash-like) to vertical and wider than intervessel-pits. Gum is visible in vessels. Axial parenchyma is vasicentric or in narrow bands up to four cells, 3-4 or 5-8 cells per parenchyma strands (Fig. 22A, B). Rays 1-4 seriate, abundant (15-20 per mm), uniseriate rays are heterocellular composed of square and upright cells, pluriseriate rays are composed of procumbent cells with over 4 rows of upright and / or square marginal cells (Fig. 22C, D). Ray height range is 131-524 µm (4-26 cells), wide range is 20-32 µm (1-3 cells). Fibers are not septate (Fig. 22D). No crystals were observed in parenchyma cells.

The combination of diffuse-porous wood, simple perforation plates, vessels solitary or in radial multiple, axial parenchyma vasicentric or in narrow bands diffuse-in-aggregates, heterocellar 1-4 seriate rays with 2-4 or more marginal cells, cannot be related to Psorospermum ‌(Dechamps 1983). Indeed, Psoropermum (Guttiferae) has vessels arranged in diagonal and/or radial pattern, tracheid fibers and rays that are wider than those observed in the Shungura fossil. Twf 17804 is close to woods of the Myrtaceae (Metcalfe & Chalk 1950; InsideWood 2004-onwards) and notably to Syzygium showing more vessels in radial than Eugenia. In Ethiopia, there is only one variable indigenous species S. ‌guineense ‌Willd. DC. (Friis 1995). Twf 17804 differs from others African species: S. ‌parkeri ‌Labat & Schatz, S. ‌cuneifolium ‌Boj., S. ‌danguyanum ‌Labat & Schatz, S. ‌micropodium ‌Labat & Schatz and S. ‌bernieri that have fewer rays per mm and no vestured pit. So, Twf 17804 seems more similar to the Ethiopian S. ‌guineense than to any other African species.

A fossil specimen identified as Syzygium was described from the Middle Awash Valley of Ethiopia where it is dated 4.4 Ma (Jolly-Saad et al. 2012). However, it differs from the Shungura specimen Twf 17804 in having bigger vessels and more vessels per mm². Twf 17804 differs from other paleobotanical species, such as (Barringtonioxylon ‌allamblackiodes ‌Lemoigne from the Upper Omo Valley (Lemoigne 1978) or Myrtoxylonsecretans ‌Boureau (Boureau 1953) and Myrtoxylon ‌kirdimiense ‌Koeniguer (Koeniguer et al. 1971) also attributed to Myrtaceae.

In conclusion, Twf 17804 is identified as Syzygium cf. guineense.

Ethiopia•Lower Omo Valley, Shungura Formation, locality L 28 sect. 3; Member F-3-2, 2.3 Ma; R. Bonnefille leg.; Twf 17995; Tervuren collection.

Twf 17995 is well preserved and wood diffuse-porous. Vessels are 9-14 per mm², solitary (48%) and also in radial multiples of 2-5 (Fig. 23A, B); mean tangential diameter of vessel is 200 µm (range 115-322 µm), mostly round to oval in outline; vessel walls thin; perforation plates exclusively simple with oblique end walls; intervessel-pits are alternate about 5-6 µm across (Fig. 23E), vessel-ray pits are indistinct. Gum deposits are visible in vessels. Rays are 1-3 (4) seriate, heterocellular composed of procumbent, square upright and procumbent cells mixed throughout the rays, mean rays height is 600 µm (range 538-1981 µm), uniseriate rays with only upright cells of multiseriate rays composed of procumbent and upright cells (Fig. 23F); marginal rows 1-4 of upright cells (Fig. 23C, D), mean ray width 100 µm (range 86-120 µm); no crystalliferous elements observed; radiovascular pits are not observed. Axial parenchyma is vasicentric with one or two rows of flattened cells and apotracheal diffuse in-aggregates (Fig. 23B). Fibers have medium-thick walls, predominantly non-septate, but are occasionally septate (Fig. 23D).

Micro-anatomical features of Twf 17995 such as solitary (or in short radial group) vessels, 1-3 seriate heterocellular rays, apotracheal parenchyma in narrow tangential bands (Fig. 23B) are structures found in the wood of Malvaceae subfamily Grewioideae. Twf 17995 was previously identified as Crotalaria L. (Dechamps 1983). However, in Crotalaria vessels are narrow (average tangential diameter ca. 34 µm), and numerous (129 per mm²), mostly in radial to diagonal pattern; axial parenchyma scanty paratracheal or in incomplete uniseriate sheaths (C. ‌capensis, C. ‌pallida), or vasicentric, in 1–3 seriate sheaths near vessels and vessel groups, strands of 2–4 cells (also fusiform in C. ‌pallida); rays are 1-3 (4)-seriate, composed of procumbent and square cells with upright cells in 1-3 marginal rows and in incomplete sheaths or mostly of procumbent cells, sometimes with few square and upright cells in 1-5 marginal rows and as solitary sheath cells (Oskolski et al. 2014). In C. ‌capensis silica bodies are common in ray and axial parenchyma cells (Oskolski et al. 2014). Therefore, we exclude the attribution to Crotalaria.

Among the Grewioideae, Grewia is easily recognized by it’s characteristic ray structures with tile cells. There are many species of Grewia in tropical Africa and 21 species in Ethiopia (Vollesen & Demissew 1995), some of which are excluded because they have storied lower rays, non-storied high rays and parenchyma vasicentric or seemingly banded (InsideWood 2004-onwards). Other species have storied rays and fibers (cf. G. ‌eriocarpa ‌Juss). G. ‌coriacea ‌Mast. and G. ‌oligoneura ‌Sprague rays are composed of procumbent cells with one or two rows of square and upright cells. G. ‌trifloral ‌Walp., G. ‌bicolor, and G. ‌flavescens from Ethiopia are similar to the fossil and can be separated from other African species by their axial apotracheal parenchyma diffuse-in-aggregate (Inside wood 2004). In the modern riverine forest of the Lower Omo Valley, Carr (1998) identified five species of Grewia, G. ‌fallax ‌K. Schum (syn. G. ‌arborea ‌(Forssk.) Lam.), G. ‌ferruginea ‌A. Rich. (syn. G. ‌beguinotii ‌Lanza), G. ‌parvifolia ‌Hochst. ex A. Rich., G. ‌reticulata ‌Hochst. ex. Mast.), and G. ‌tembensis ‌Fresen. (syn.: Grewia ‌membranacea ‌A. Rich) for which we have no microanatomical descriptions. Without more detailed information on the wood anatomy of the different Ethiopian species, Twf 17995 remains identified as Grewia sp.

Grewioideae fossil record is sparse (Manchester 1992; Gregory et al. 2009). Many fossil woods close to Grewia are described under the morphotype Grewioxylon from Asia and Europe, but not from Africa.

Ethiopia•Lower Omo Valley, Shungura Formation, locality L 28 sect. 3; Member F-3-2, 2.30 Ma; American Staff leg.; Twf 17949A; Tervuren collection.

The three thin sections of the specimen are very poorly preserved; several features are indistinct. The wood is diffuse-porous, growth rings are absent or indistinct (Fig. 24A). Vessels are mostly solitary or in radial multiple of 2 or 3, they are 3-7 per mm², mean tangential diameter 80 µm (range 46-115 µm) (Fig. 24A, B). Vessel element length is indistinct, perforation plates are simple, intervessel-pits are minute (< 4 µm). Although not well preserved they appear probably vestured. Axial parenchyma is diffuse-aggregate (Fig. 24B). Pluriseriate rays are composed of wide procumbent cells with 1-5 rows of square cells and upright cells. Pluriseriate rays (1-4 seriate) are high (1 mm and more) with distinct sheath cells (Fig. 22D). Uniseriate rays are exclusively composed of high upright cells and are shorter than pluriseriate rays (Fig. 23D), ray range height is 108-575 µm, ray width is 13-50 µm. Prismatic crystals and silica are distinct in ray cells, at times in enlarged cells. Fibers are septate. The radial section shows perforated cells (Fig. 24F).

Micro-anatomical features of the fossil wood include mostly solitary vessels with a few in radial multiple, mean vessel diameter is less than 100 µm, diffuse-in-aggregate parenchyma, heterocellular rays of two sizes and large prismatic crystals in ray cells. The presence of perforated cells and these combined characters do not fit the attribution to Garcinia ‌(Dechamps 1983). More likely, the specimen shows greater affinity with some Rubiaceae or Ochnaceae. The presence of perforated cells and large rays is particularly indicative of the Ochnaceae family. Within the Ochnaceae, the wood of Ouratea differs from Twf 17949A by having longer and thinner rays. The Omo fossil wood shows greatest resemblance with the wood of Ochna. From the Ethiopian flora, two species restricted to montane forest (Friis 1992)O. ‌holstii ‌Engl. have no perforated cells and O. ‌insculpta ‌Sleumer is not documented. Among other species O. ‌afzelii ‌R. Brown ex Oliv. and O. membranacea ‌Oliv. have vascular/vasicentric tracheids and perforated cells. O. polycarpa ‌Baker has no perforated cells (InsideWood 2004-onwards). O. arborea ‌Burch. ex DC., O. ‌calodendron ‌Gilg & Mildbr., and O. ‌multiflora ‌DC are species similar to our studied fossil species, but they are not found in Ethiopia today.

We do not know any fossil wood reported to the Ochnaceae or to Ochna in Africa. Ochnaceoxylon tertiera described from the Tertiary in Deccan (India) has vasicentric parenchyma and wide rays (Ramteke & Kapgate 2016).

Twf 17949A is attributed to Ochna sp. 1

Ethiopia•Lower Omo Valley, Shungura Formation, locality L 28 sect. 3, Member F-3-2, 2.30 Ma; American staff; Twf 17950A; Tervuren collection.

Twf 17950A displays heterogeneously preservation, with notable alterations observed in tangential section. The wood is diffuse-porous and growth rings are not present. Vessels are rounded in outline, mostly solitary (58 %) and in radial multiples of 2 (21 %), 3 (9 %), 4 (4 %), 5 (4 %), 6 (0.8%), 7 (1.6%) (Fig. 25A), there are 40-65 per mm². Mean tangential diameter of 40 µm (range 25-53 µm); perforation plates are exclusively simple, vessel elements are short (range 81-100 µm); intervessel-pits are alternate, 5-6 µm wide and they may be vestured (Fig. 25E), vessel-ray pits are indistinct; vessel wall thickness is about 5 µm. Black and yellow deposits are distinct in vessels. Rays are (1)-4 seriate, 5-7 per mm, heterocellular, composed of procumbent with 1-4 row of square and upright cells, mean rays height is 1500 µm (range 780-2200 mm), mean ray width varies between 75 µm to 80 µm, uniseriate rays are exclusively composed of square and upright cells. Some rays are interconnected. Sheath cells are distinct (Fig. 24D). Prismatic crystals are distinct in ray cells (Fig. 25B). This specimen clearly exhibits distinct perforated cells (Fig. 25F).

Apocynaceae and Rubiaceae have members exhibiting radial multiples of four or more vessels, simple perforation plates, alternate, minute intervessel-pits, and septate fibers are found. Rubiaceae can be identified by several unique characteristics: vestured intervessel-pits, vessel density of 20-40 vessels per square millimeter, very long vessel elements, diffuse and diffuse-in-aggregates axial parenchyma, scanty axial parenchyma, and narrow heterocellular rays that are 1-3 (rarely 4) cells wide with 1 to over 4 uniseriate marginal rows (Metcalfe & Chalk 1950; Jansen et al. 2001). Among this family, Canthium, Crossopterix ‌febrifuga, Gardenia ‌terniflolia, Nauclea ‌latifolia and Rothmannia have axial parenchyma diffuse and diffuse-in-aggregates (InsideWood 2004-onwards), a character that we have not observed in the Omo fossil wood. Rothmannia has shorter rays. Twf 17950A has particular similarities to Psychotrieae, including Psychotria. In Ethiopia, Psychotria ‌capensis grows in riverine forest, between 1150-1300 m. For Psychotria ‌kirkii, P. ‌pedicularis, P. ‌orophila, the three taxa from montane evergreen forest, no xylo-anatomical data exist.

Fossil wood specimens identified as Rubiaceae in Africa are known since the Oligo-Miocene with Mitragynaxylon ‌gevini ‌Gevin from the Tindouf of Algeria differing from the Omo fossil specimen with solitary vessels and 1-3 seriate rays (Gevin et al. 1971). A specimen belonging to the Rubiaceae was described from the Early Miocene Gebel El-Khashab Formation, located west of the Giza Pyramid in Egypt. This specimen differs from the Omo fossil wood by having both simple and scalariform perforation plates (El-Saadawi et al. 2016). Rubioxylon ‌vincenti ‌Boureau & Koeniguer from the Miocene of the Upper Omo Valley is described with scalariform perforation plates (Lemoigne 1978). Rubioxylon ‌vincenti ‌Koeniguer from the Plio-Pleistocene of Angamma in Chad has uniseriate rays (Koeniguer 1975). All these fossil specimens differ from Twf 17950A that is attributed to an extant species of Psychotria sp. (Table 4).

Ethiopia•Lower Omo Valley, Shungura Formation, locality L 28 sect. 3; Member F-3-2, 2.3Ma; R. Bonnefille leg.; Twf 18028; Tervuren collection.

Twf 18028 comprises a well-preserved cylinder displaying mineralized heteroxylous wood structure, representative of a stem fragment. The wood is diffuse-porous or noticeably semi-porous, with areas of higher concentrations of vessels (Fig. 26A). Vessels mostly solitary (90 %) other in short radial multiple of 2 and 3, clusters are absent (Fig. 26B). Vessels are rounded in outline with mean tangential diameter of 30 µm, (18 µm up to 45 µm); 40-70 per mm²; wall thickness about 5 µm. Perforation plates are exclusively simple and horizontal and vessels are short (range 81-100 µm); intervessel-pits are alternate, oval and 5-6 µm wide. Black and yellow deposits are distinct in vessels. Axial parenchyma is scanty paratracheal (Fig. 26B). Rays are 1-6 seriate, uniseriate rays are composed of upright cells, pluriseriate rays composed of procumbent cells with long ends of 4 or more than 4 rows of upright cells (Fig. 26C, D), 11-12 per mm, mean ray height is 850 µm (range 495 to 1848 µm), mean ray width range 34-36 µm, sheath cells distinct (Fig. 26C). Fibers are medium to thick walled; pits or septae are not observed in tangential section.

Twf 18028 was first identified as Diospyros (Dechamps 1983; Dechamps & Bande 1994). However, anatomical features such as mostly solitary vessels, heterocellular multiseriate rays, scanty paratracheal parenchyma, and long heterocellular rays with sheath cells, rather indicate affinities with the Rubiaceae. According to the comparison with some genera of the Rubiaceae family in the Ethiopian flora, some similarities exist between Twf 18028 and Rothmannia.

Few Rubiaceae fossil woods have been described from Africa. Rothmannia was identified from the early Pliocene of the Middle Awash Valley, Ethiopia, and dated 4.3 Ma (Jolly-Saad et al. 2012). However, Twf 18028 differs with the Middle Awash sample by the presence of disjunctive ray cell, 1-3 seriate ray cell and the absence of tracheid fibers. Twf 18028 may represent a distinct younger species. Among other fossil species from Ethiopia, we can exclude Rothmannia ‌aethiopica (Gros 1990, later invalidated by Gregory et al. 2009), and Rothmannia ‌omoensis ‌(Gros 1990) characterized by numerous small to medium-sized vessels, uni to pluriseriate rays, diffuse axial parenchyma, and the presence of tracheids. In conclusion, Twf 18028 remains identified as Rothmannia sp. with no mention of a specific attribution.

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 560-2 sect. 9; Member G-3, 2.19 Ma; American Staff leg.; Twf 17712; Tervuren collection (Fig. 27)•same data; locality P 388 sect 19, Member G-5, 2.13 Ma; Twf 17665; Tervuren collection (Fig. 28).

Twf 17712 is poorly preserved. But Twf 17665 shows anatomical features (axial parenchyma vasicentric, confluent, seemingly banded, ray heterocelluler 1-6 seriate, prismatic crystals in ray cells and intervessel-pits not vestured) and quantitative values comparable to those previously described for Twf 17812 (Fig. 28) that was identified as Celtis cf. integrifolia. All these characters are summarized in Table 3.

Twf 17712 and Twf 17665 were initially attributed to Lannea or Ozoroa among Anacardiaceae ‌(Dechamps 1983). However, the presence of abundant parenchyma contradicts this diagnosis, as both genera exhibit sparce parenchyma. Furthermore, Ozoroa is characterized by larger vessel pits, septate fibers and does not have prismatic crystals in ray. Therefore, we exclude such previous identification.

From Africa, three generic names, Celtisoxylon Trivedi, Celtixylon ‌Greguss, and Celtoxylon Wurzinger have been attributed to fossil woods resembling Celtis, although not properly diagnosed (Gregory et al. 2009). Celtisoxylon applied to a wood from Deccan Intertrappean beds of India was only mentioned in an abstract without description and designation of holotype. Celtixylon was never formally diagnosed, and Celtoxylon was used in a thesis, not formally published. Woods thought to have affinities with Celtis have been reported from the Miocene of temperate Europe and Asia (Selmeier 1989) and North America (Wheeler & Manchester 2021).

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 794 sect. 5, Member G-5, 2.13 Ma; Jean de Heinzelin leg; Twf 17640; Tervuren collection.

The preservation is quite good in the transverse section, but moderate in the tangential section where all the cellular details are not very clear. Wood is diffuse-porous, growth rings boundaries are absent, vessel are solitary (23 %) and in radial multiples of 2 (59%), 3 (15%) and 4 (3%) (Fig. 29A, B), 12-25 per mm². Mean tangential diameter of 76.4 µm, range 24-118 µm. Perforation plates are exclusively simple, vessel elements are not distinct, intervessel-pits are 3-4 µm wide, probably vestured but the details are hard to distinguish (Fig. 29E), vessel-ray pits are not visible. Gum deposits are observed in vessel lumina. Parenchyma is scanty paratracheal, diffuse-in-aggregates (Fig. 29B), parenchyma strands are not clearly distinct, probably 5-8 cells per strands. Rays are 1-4-seriate and heterocellular; uniseriate rays are composed of upright cells, multiseriate rays composed of procumbent cells with one row of upright cells. 4-5 per mm, mean ray height is 800 µm (range 414-1092 µm) (3-23 cells), mean ray width is 60 µm (range 31-92 µm). Fibers are thin to medium walled of various size and shape. Septate and not septate fibers are observed, strands of crystalliferous axial parenchyma with one rhomboidal crystal per chamber (Table 4).

Anatomical features of Twf 17640 such as vessels in radial multiple, perforation simple, small vestured intervessel-pits, axial parenchyma scanty paratracheal and diffuse-in-aggregates, 1-4 seriate heterocellular rays are wood characteristics similar to those of the Rubiaceae (Jansen et al. 2002; Inside-wood). In Ethiopia, this botanical family includes 31 genera as trees or shrubs (Puff 2003) (Friis et al. 2011). For the comparison with the fossil Twf 7640, we exclude all the species having exclusively solitary vessels such as Catunaregam ‌Wolf, Coffea L. (C. ‌arabica L.,C. ‌richardii ‌Leroy, Gardenia ‌Colden, Mitragyna ‌(Wild.), Paederia L., Sarcocephalus ‌latifolius ‌(Smith) Bruce,Tricalysia ‌DC., Feretia ‌Del., Pavetta L., Psilanthus ‌Hook f., Keetia ‌E.P. Philips, Tarenna ‌Gaertn., Rytigynia ‌Blume, Uncaria ‌Schreb.Paederia and Vangueria ‌Juss.). In the group of taxa comprising vessels in small radial multiple up to 3 rarely, vessels in small radial multiple up to 3 rarely 4, Anthospermum L., Breonadia ‌salicina and Hymenodictyon ‌floribundum ‌(Hochst. & Steud.) Robinson have scarce axial parenchyma and thinner rays. Galiniera ‌Del., Hymenodictyon, Mussaenda L. have thinner rays. Craterispermum ‌Benth., has banded parenchyma. Carphalea ‌Juss. has wider rays and crystals in enlarged cells. Psydrax ‌schimperianus ‌(A. Rich) Bridson has no crystal in ray cells. Psydrax ‌parvifolia has larger rays. We have no available microanatomical data for Chazaliella ‌E.M.A. Petit & Verdc., Meyna ‌Roxb. ex. Link, or for Polysphaeria ‌Hook f., to compare with Twf 17640 and sample Twf 17714.

Anatomical characteristics, including diffuse porous wood, scanty paratracheal and diffuse-in-aggregate axial parenchyma, rays heterocellular composed of procumbent cells and 1-4 rows of square and upright marginal cells, as well as small and probably vestured intervessel-pits, are found in modern Rubiaceae such as Canthium sp. 1.

Ethiopia•Lower Omo Valley, Shungura Formation, locality L 560-1; Member G-3, 2.13 Ma; American Staff leg; Twf 17714; Tervuren collection.

Twf 17714 exhibits very similar characteristics to Twf 17640, but with some differences (Table 5) justifying an attribution to a distinct species Canthium sp. 2, illustrated in Figure 30.

A small number of Rubiaceae fossil wood morphotypes are known from Africa; the oldest dating from the Oligocene-Miocene (Gevin et al. 1971). In Ethiopia, Rubioxylonvincenti ‌Boureau & Koeniguer, briefly described from the Miocene of the Upper Omo Valley (Lemoigne 1978), has thinner rays and scalariform perforation plates.Rubioxylon ‌vincenti ‌Koeniguer from Pliocene deposits in Chad has uniseriate rays, medium-sized vessels, and paratracheal vasicentric parenchyma (Koeniguer 1975). Rothmannia cf. R. ‌whitfieldii from the Sagantole Formation at Aramis locality, Middle Awash (Ethiopia) and dated 4.3 Ma shows solitary vessels, thinner rays and disjunctive ray cells, and does not resemble the Omo fossil specimen Twf 17640. Another fossil from the Lower Omo Valley (Pa 8036A), collected by Coppens et al. was assigned to Canthium ‌omoense ‌(Gros 1990) in Member G28–29 (Argile du Château), differs from the two specimens studied here (Twf 17640 and Twf 17714). This fossil specimen differs from the Shungura specimens by the absence of diffuse-in-aggregates parenchyma.

In conclusion, the closest affinities of the fossil specimen Twf 17640 are with the extant genus Canthium in the Vanguerieae ‌A. Rich. (Gros 1990; Lens et al. 2000; Mouly et al. 2021). It is considered as Canthium sp. 1, a distinct species from Canthium sp. 2 showing non-septate fibers (Table 4), attributed to Twf 17714 (Fig. 30) a wood sample moderately preserved, collected from a slightly younger stratigraphic Unit G-3 (Table 2).

Ethiopia•Lower Omo Valley, Shungura Formation, locality L 35-58 sect. 4, Member G-5, 2.13 Ma; American Staff leg; Twf 17615; Tervuren collection.

Due to poor preservation, several anatomical features of the specimen are unclear or indistinct. The wood is diffuse-porous and growth rings boundaries indistinct. Vessels are solitary (77%) and in radial multiples of 2-3, 1-2 per mm². Mean tangential diameter of 213 µm, range 81-345 µm. Perforation plates exclusively simple; vessel elements are not clearly distinct (n=1: 189 µm), vessel pits are indistinct. Sclerotic tyloses are visible in vessel lumina. Axial parenchyma abundant, banded; bands are 4 cells wide (46 µm) up to 14 cells (230 µm); strands of parenchyma 5-8 cells. Rays are 2-6-seriate, heterocellular, composed of procumbent with one row of upright cells. 4-5 per mm. Length is between 414 µm to 1092 µm and 31 to 92 µm wide. They are 4-5 per mm. Fibres are not septate.

Twf 17615 characteristics are: vessels that are solitary and in radial multiples, simple perforation plates, alternate intervessel-pits, thick-walled fibers, banded axial parenchyma, which is storied and fusiform. As some diagnostic features are not visible due to the poor preservation of the wood, it is not possible to provide a diagnosis for Twf 17615.

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 719 sect. 18 Member G-13, 2.06 Ma; Jean de Heinzelin leg.; Twf 17754; Tervuren collection.

The preservation of Twf 17754 is relatively good, with distinct fungal hyphae visible within the vessel elements. The wood is diffuse-porous, growth rings boundaries indistinct (Fig. 31A, B). Vessels are round or oval in shape mostly solitary (90%), few of them in short radial multiples of 2 or 3, clusters distinct. There are 10-15 vessels per mm². Vessel wall is thin (2-3 µm). Gum deposits are distinct in vessel lumina. Mean tangential diameter is 172 µm (range 92-253 µm). Mean vessel element height is 340 µm (range 364-405 µm). Perforation plates are exclusively simple and horizontal. Intervessel pits are vestured, alternate, 4-5 µm wide (Fig. 31E), some are coalescent, vessel-ray pits are similar to intervessel pits. Axial parenchyma has various distributions, vasicentric unilateral (1 to 3 rows of cells), vasicentric and often confluent up to 3 vessels. Parenchyma strands have 2-4 cells. Rays are 1-3 (4) seriate wide (Fig. 31C), 9-10 per mm. Mean ray height is 500 (range 104-1380 µm; 8-12-91 cells), mean ray width is 30 µm (range 21-54 µm). They are composed of procumbent cells and 1-2 rows of square and upright cells. Prismatic crystals are distinct in chambered parenchyma up to ten strands. Fibers are irregular thin to medium thick walled, range in diameter is between 8-14 µm; no pits or septae have been observed.

This fossil exhibits several distinctive anatomical features including diffuse-porous wood, simple perforation plate, large vessels, parenchyma vasicentric unilateral, vestured pits, long homocellular rays 1-5 seriate. These features clearly indicate affinities with the Fabaceae family, but not with Bridelia (Phyllanthaceae) as previously suggested (Dechamps 1983). Comparison of Twf 17754 with various Fabaceae shows that few species combine axial unilateral parenchyma and vestured pits. Among them, Erythrophleum is the most similar. Within the genus, E. ‌suaveolens most closely resembles the wood anatomy of the Twf 17754 specimen.

Erythrophloeoxylon was identified as a fossil morphotype close to Erythrophloeum ‌(Müller-Stoll & Mädel 1967). In Africa, one fossil species, Erythrophleum ‌africanum, was mentioned from the Pliocene of the Lower Omo valley (Dechamps 1976). However, no description, illustration, or thin section of this material was provided. A fossil taxon most closely related to Twf 17754 appears to be Peltophoroxylon ‌embergeri ‌Lemoigne from the Upper Omo valley (Lemoigne 1978). This wood exhibits diffuse porosity and less vessels (8-10 vessels per mm²), vasicentric or vasicentric unilateral parenchyma and wider (2-6 seriate) rays than our sample. In conclusion, based on the observed anatomical features and comparative analysis, we attribute Twf 17754 to Erythrophleum sp.

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 553 sect. 6, Member G-18, 2.12 Ma; Jean de Heinzelin leg.; Twf 17707; Tervuren collection.

The fossil exhibits poor preservation, and the longitudinal section has not the appropriate thickness for detailed analysis. The wood displays diffuse porosity. The presence of a growth ring is discernible (Fig. 32A), exhibiting the reduction of fiber diameter in three or four rows and variation in vessel density. Vessels are solitary (47%) or in radial multiple of 2 (21%), 3 (14%), 4 (7%), 5 (8%), 6 (2%) and 7 (1%); 100 and more per mm² (Fig. 32A, B). Mean vessel diameter is 22 µm (range 13-42 µm), perforation plates are simple, horizontal to sightly oblique. Vessel elements are short 108-112 µm. Intervessel pits are crowded alternate, minute to small (3-4 µm), bordered, and not vestured (Fig. 32E). In radial section, vessel-ray pits are similar to vessel pits. Rays are uniseriate, exceptionally biseriate with sometime uniseriate ends (Fig. 32C, D). They are composed of procumbent cells with one row of square and upright cells. Mean ray height is 135 µm (range 50-227 µm; 4-19 cells), mean ray width is 15 µm (range 8-20 µm). Fiber diameter is between 9 to 22.4 µm, apparently not very thick-walled. Parenchyma is rare, scanty paratracheal and apotracheal.

The combination of anatomical features observed in Twf 17707 including: narrow vessels occurring solitary or in long radial multiples, minute to small alternate intervessel pits, and narrow rays primarily composed of procumbent cells does not support initial identification as Populus ‌euphratica ‌(Dechamps 1983). Species of Populus typically exhibit larger vessel pits and exclusively uniseriate rays. Instead, the wood anatomy of Twf 17707 shows close affinities with families such as Asteraceae and Rutaceae (including Ptaeroxylaceae ‌(APG II, 2003). Among the Asteraceae, Brachylaena exhibits both thin and storied rays, a feature consistent with the anatomy of Twf 17707 that represents the first fossil wood specimen described for this family in Africa (Gregory et al. 2009). Indeed, among the Rutaceae, we can exclude the morphotype Ptaeroxylon for its occurrence of prismatic crystal, a character not seen in our fossil.

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 729 sect. 19, Member G-19, 2.01Ma; R. Bonnefille leg.; Twf 18069; Tervuren collection.

Twf 18069 is a small branch that retains evidence of central pith. The wood is diffuse-porous, growth rings absent. Vessels are solitary (73%) and in radial multiples of 2 (22%), 3 (2%). Mean tangential diameter of 70 µm, range 21-115 µm, 15-20 vessels per mm² (Fig. 33A). Perforation plates are exclusively simple; intervessel-pits crowded alternate, bordered, minute and vestured (fig. 33E); vessel-ray pits are similar to intervessel-pits (Fig. 41E); Gum is visible in vessels. Axial parenchyma is vasicentric, aliform to confluent, strands of cells 2-3. Rays are 1-3 (4) seriate, heterocellular, composed of procumbent and square cells mixed throughout the rays and showing uniseriate ends (Fig. 33C, D). Rays are not storied, 10-12 per mm, mean ray height is 300 µm (range 172-483 µm), mean ray width is 40 µm (range 22-80 µm). Fibers are thick with mostly very thick wall, septae present. Crystals are distinct in parenchyma and in ray cells.

Twf 18069 is characterized by diffuse-porous wood, small to medium-sized vessels, solitary or in radial multiple, predominantly paratracheal parenchyma that is vasicentric to sightly aliform, confluent, 1-3 seriate heterocellular rays, septate fibres, and crystal inclusions in rays and parenchyma. Twf 18069 was initially identified as Acacia ‌mellifera ‌(Dechamps 1983). But the presence of heterocellular rays, with mixed procumbent square cells throughout the ray structure, along with the occurrence of mineral inclusions in the ray cells, challenge the original identification.

These features are not characteristic of Acacia, which typically exhibit homocellular rays with procumbent cells. Instead, the anatomical characteristics of the specimen, particularly the ray cells composition and mineral inclusions, more closely resemble those observed in Terminalia L. (Inside Wood online-2004-onwards (Van Vliet 1979). Consequently, Twf 18069 is attributed to Terminalia sp.

Twf 18069 also shares some diagnostic features (mostly, rays with procumbent cells and square cells mixed in the rays with one row of upright cells, intervessels pits vestured, druses in chambered parenchyma and crystals in rays) with Terminalioxylon ‌G.Schönfeld, a palaeo­botanical taxon of worldwide distribution recorded with more than 60 fossil species described from the Eocene to the Miocene in Africa (Gregory et al. 2009). All these fossil species differ from Twf 18069 with their exclusively uniseriate rays, bigger vessels, and in ray composition for some of them.

We rather refer Twf 18069 to the extant genus Terminalia. However, with regards to the great number (150) of modern African species (Mabberley 1997), including nine from Ethiopia (Vollensen 1995a), a specific attribution remains impossible in the current state of knowledge. We can exclude Terminalia ‌brevipes ‌Pamp., common from riparian forests in Southern Ethiopia and previously described (Jolly-Saad & Bonnefille 2023). In conclusion, we report Twf 18069 (Fig. 33) to Terminalia sp.

Ethiopia•Lower Omo Valley, Shungura Formation, locality Omo 27-2, Member G-18, 2.02 Ma; R. Bonnefille (73-5) leg.; Twf 17929; Tervuren collection.

Twf 17929 is not well preserved. Wood diffuse-porous, growth ring boundaries are indistinct. Vessels are mostly solitary (86 %) or grouped by 2 (12 %), 3 (1%) and rarely cluster (1%), 4 to 12 per mm² (mean 8) (Fig. 34A). Mean tangential diameter is 126 µm, range 57-195 µm, vessel wall thin (2-3 µm wide). Tyloses are absent. Vessel element length is not visible. Perforation plates are exclusively simple, intervessel pits alternate (4-5 µm) are vestured and not crowded (Fig. 34E). Vessel-ray pits are similar to intervascular pits. Axial parenchyma is mostly vasicentric, slightly aliform, sometimes confluent. Prismatic crystals are distinct in chambered parenchyma cells (14 µm wide). Rays are 1-6 (8) seriate wide, uniseriate rays are rare, 6-9 per mm. Mean ray height is height is 400 µm (range 90-805 µm), mean ray width is 60 µm (range 9-72 µm). They are composed of procumbent cells (Fig. 34C, D-F). Fibers show poorly distinct walls, diameter of fibers range is 5-11 µm, pits are not observed and septae visible (Fig. 34D).

The most characteristic features of Twf 17929 are diffuse-porous wood, vessels solitary or in radial of 2-3, axial parenchyma paratracheal vasicentric, aliform, sometimes confluent, vessel pits vestured, 1-6 (8) seriate rays with only procumbent cells, prismatic crystals in chambered parenchyma, fibers are septate. These features are found in modern Fabaceae and particularly in the Mimosoideae subfamily (now in the recircumscribed Caesalpinioideae subfamily) (LPWG 2017). In modern wood of Mimosoideae, the parenchyma aliform, confluent, rays with procumbent cells combined with the presence of septate fibers are mainly found in two African genera: Albizia ‌Inga Mill. and Pithecellobium ‌Mart (InsideWood 2004-onwards). Our fossil wood is more likely attributed to Albizia.

A previously described Pliocene sample Twf 17638, also attributed to Albizia showed affinities with the Ethiopian species A. ‌autunensis ‌(Jolly-Saad & Bonnefille 2012). In this study, because of the lack of data on other species, the most reasonable attribution of Twf 17638 is Albiza sp. 1. Sample Twf 17929 is slightly different and, therefore considered Albizia sp. 2.

From the Ethiopian flora we exclude some forest species such as A. ‌coriaria ‌Welw. Ex Oliv., A. ‌isenbergiana and A. ‌petersiana having 1-3 seriate rays whereas they are 1-4 seriate in A. ‌grandibractea and 2-5 seriate in A. schimperiana (Jolly-Saad et al. 2012; Table 5). Based on these comparisons, Twf 17929 is definitely assigned to Albizia. Its anatomical characters do not match those of Albizia sp. 1 (Twf 17638) from the late Pliocene characterized by 1-8 seriate rays (Table 2), It is also distinct from Albizia type gummifera, a Miocene wood (MA 94-73C) of the Middle Awash valley (Ethiopia), dated 5.8 Ma. This older specimen displays fewer vessels per square millimeter (2-5/mm2) and 1-6 seriate rays (Jolly-Saad et al. 2012; Table 4).

Among morphotypes, Mimosoxylon ‌mbakkaouense ‌Dupéron-Laudoueneix from Cameroon exhibits 1-3 seriate thinner rays (Dupéron-Laudoueneix 1991; Gros 1992). In conclusion, this fossil is attributed to a new species Albizia sp. 2 (Fig. 33).

Ethiopia•Lower Omo Valley, Shungura Formation, locality O 27-2, Member G-19, 2.01 Ma; R. Bonnefille 73-6 leg; Twf 17928; Tervuren collection.

Fossil wood very poorly preserved with diffuse-porous wood and indistinct growth rings. Vessels are solitary (56%) or in radial multiple of 2 (31%), 3 (7%), 4 (4%) up 5 (2%), clusters are absent; vessels are 2-11 per square, circular (Fig. 35A, B). Mean tangential diameter of 145 µm, range (67-160 µm). Perforation plates are not distinct because of important tyloses in vessels; vessel elements, intervessel pits and vessel-ray pits are not clearly visible. Axial parenchyma banded or irregularly banded forming seriate tangential row, marginal bands composed of three up to 5 or 6 cells, number difficult to evaluate due to the poor preservation of this sample. Parenchyma strands of 5-8 cells are locally storied. Rays are commonly 1-8 seriate and some are more than 10 cells wide, uniseriate are rare, exclusively composed of square and upright cells, pluriseriate rays are composed of procumbent cells with 1-3 rows of marginal square and upright cells (Fig. 35C, D). Rays are 6-10 rays per mm, mean ray height is 60 µm (range 23-79 µm) and width ranges from 107 to 670 µm. Fibers are thick walled and not septate. Rhomboidal crystals are distinct in ray cells and prismatic crystal in parenchyma.

Initially identified as Myrianthoxyln coppensii, the misidentification of Twf 17928 is due to its poor preservation. Twf 17928 differs from Myrianthus due to the presence of challenging regular parenchyma bands. Additionally, features such as irregular rays and locally storied parenchyma strands in a tangential section suggest closer affinities with Ficus, without any more precision upon the species attribution than Ficus sp. 1 (Table 5).

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 742 sect. 22, Member G-29, 1.92 Ma; Jean de Heinzelin leg.; Twf 17823, Twf 17830; Tervuren collection.

Twf 17823 and Twf 17830 closely resemble a fossil wood fragment from Member C-5 in the Pliocene, Twf 17839, fully described and attributed to Borassus sp. 1 (Arecaceae; Fig. 11). The two samples from G-29 in the Pleistocene are also similar as illustrated in Fig. 36, and therefore attributed to the same species Borassus sp. 1 (Table 2), in agreement with former identifications (Dechamps 1983).

Ethiopia•Lower Omo Valley, Shungura Formation, Member G-29, locality P 726 sect. 19; Jean de Heinzelin leg.; Twf 17770; Tervuren collection.

Twf 17770 is not well preserved. Wood is diffuse-porous. Growth rings are slightly marked by the reduction of fiber diameters on two up four rows. Vessels are solitary (67.5 %) or in radial multiple of 2 (17.5 %), 3 (10 %), 4 (2.5 %) and 5 (2.5 %), they are more than 100 per mm² (Fig. 37A, B). Mean vessel tangential diameter of 30 µm, range (20-37 µm). Perforation plates are exclusively simple; vessel-pits crowded alternate, minute (< 4 µm). Vessel wall is thick 6-7 µm. Vessel elements length and parenchyma strands are not distinct because of the poor preservation of the longitudinal section and high permineralization in vessels lumina. Axial parenchyma is rare, scanty paratracheal, it is difficult to distinguish it from fibres in longitudinal section. Rays are uniseriate, rarely bi-seriate composed of procumbent cells with one row of upright cells, more than 12 per mm. Rays are short, mean height 250 µm (225-301 µm), mean width 15 µm, they are storied, or irregularly storied (Fig. 37C). Other structures of parenchyma are not visible due to the poor preservation of the fossil wood. Fibers have very thick walled with diameter between 11-20 µm. Inclusions are absent or indistinct.

The fossil exhibits diffuse porosity, scanty paratracheal parenchyma, and uniseriate, storied rays. These anatomical features are consistent with Androstachys ‌johnsonii (Picrodendraceae, Euphorbiaceae) and Brachylaena (Asteraceae). However, Androstachys shows a higher proportion of solitary vessels (90%) and consistently storied rays. Our specimen shows the closest affinity with Brachylaena. It may represent a different species than Brachylaena sp. 1 inferred to the oldest Twf 17707 (2.02 Ma from G-18; Fig. 32). Twf 17770 from unit G-29 and dated 1.92 Ma is attributed to Brachylaena sp. 2. (Fig. 37).

Ethiopia•Lower Omo Valley, Shungura Formation, Member G-29, locality P 726 sect. 19; Jean de Heinzelin leg.; Twf 17912; Tervuren collection.

Twf 17912 is moderately preserved as can be seen in the longitudinal section where a large number of fungal hyphae are observed. The preservation in the cross section is good. Twf 17912 is diffuse-porous, growth ring are clearly defined by the large bands of dense and bigger vessels. Vessels are solitary (62 %) or in radial multiple of 2 (28%), 3 (8 %) and 4 (1 %) and with also tangential arrangement (Fig. 38A, B), density. 20-25/mm², mean tangential diameter of 80 µm (range 56-120 µm), vessels are thin walled. Perforation plates are exclusively simple; vessel elements are not distinct because of abundant tyloses; intervessel-pits are large (8-10 µm), crowded alternate and not vestured (Fig. 38F). Tyloses are abundant in vessel lumina. Axial parenchyma is extremely rare or scanty paratracheal. Parenchyma strands are not distinct. Rays are 2-4 (5) cells wide, with radial canals, heterocellular composed of procumbent cells with one or 4 rows of square and upright cells (Fig. 38C, D). Some rays are interconnected at their ends. Rays are short, mean ray height is 350 µm (range 180-600 µm), mean ray width is 50 µm (range is 25-80 µm), 7-10 per mm. Radial canals with epithelium cells are present (Fig. 38E). Vessel-ray pits have thin borders. Fibres have very thick wall and are septate. Another feature is the radial alignment of fibers in the transverse section. Crystals or silica are visible in ray cells and in tyloses.

Twf 17912 is characterized by small to medium vessels, solitary or in radial multiple of 2-4, 20-25 per square millimeter, perforation plates simple, vessel-rays pits with much reduced borders, tyloses observed, septate fibres, axial parenchyma absent extremely rare or scanty paratracheal, 2-4 (5) seriate heterocellular rays consisting of a body of procumbent cells with 2-4 rows of upright and/or square marginal ray cells, rays non-storied, radial canals, prismatic crystals present in upright and/or square ray cells, radial canal are the most important characteristics linking Twf 17912 with extant members of the Anacardiaceae and Burseraceae (Metcalfe & Chalk 1950; Inside Wood 2004-onwards). Both families have very similar anatomical features. However, the presence of septate fibres, crystals and silica in rays and the radial alignment of fibers in the transverse section are found in the Burseraceae ‌(Normand 1950). Among the homogenous characters of the Burseraceae wood, Canarium has rare axial parenchyma (Gregory et al. 2009), Boswellia has no crystal in ray cells. The Omo fossil wood is most similar to Commiphora, a genus known in Ethiopia through over 50 species.

Fossil woods of the Burseraceae family are not abundant in Africa (Gregory et al. 2009). They are grouped into two genera: Burseroxylon including fossils related to Bursera ‌Jacq. ex L. and Canarioxylon ‌Prakash, Březinová & Awasthi including fossils related to Canarium. A fossil wood known as Burseroxylon ‌africanum ‌Bamford and related to Burseraceae was documented from the early Miocene Orange River gravels in Namibia (Bamford 2003). Unlike the Omo fossil wood, this species lacks crystals in the ray cells and radial canals are absent. In conclusion, the identification of Twf 17912 is confirmed as Commiphora sp. (Fig. 38).

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 726 sect. 19; Member G-29, 1.92 Ma; Jean de Heinzelin leg.; Twf 17906; Tervuren collection.

Twf 17906 is well preserved in all three Member sections. It is a small fossil stem with a central cylinder and an estimated diameter of approximately 2 cm. Its anatomical features closely resemble Twf 17609 from B-12 (Fig. 39), as well as Twf 17805 and Twf 17808, from Member C-8 (Fig. 17). Given the shared characteristics, the specimen is attributed to Maytenus, as previously described, and most probably belongs to the same species Maytenus sp. 1.

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 743 sect. 22, Member G-29, 1.92 Ma; Franck Brown & Jean de Heinzelin leg.; Twf 17965; Tervuren collection•same data; R. Bonnefille & Jean de Heinzelin leg.; Twf 17973; Tervuren collection.

Twf 17965 is a small twig fairly well preserved. Wood is diffuse-porous. Growth rings are marked by different density of vessels repartition. Vessels are mostly solitary (91 %), 4-6 per mm² (Fig. 40A, B). Vessels of two distinct size. Mean tangential diameter of 100 µm, range 80-150 µm, thin wall. Vessel elements length are 200-250 µm; perforation plates are simple and horizontal; intervessel pits are crowded alternate, 4-5 µm wide and vestured (Fig. 40E).

Axial parenchyma is diffuse, vasicentric, aliform, confluent or seemingly banded. Parenchyma strands with 2-4 cells. Rays are 1-2 (3), they are short, mean ray height is 320 µm (range 282-424 µm (4-37 cells), mean ray width is 60 µm (range 58-78 µm), heterocellular composed of procumbent with one row of square cells, 12-14 per mm (Fig. 40C, D) Disjuntive ray cells occasionally visible. Crystals in ray cells and in chambered parenchyma in chains of 7-15 cells, 18 µm wide.

Twf 17965 and Twf 17973 exhibit identical anatomical characteristics: vessels mostly solitary, axial parenchyma vasicentric and confluent, rays 1-3 seriate, vestured pits. These features differ notably with those of MyrianthusDechamps (1983). Instead, Twf 17965 and Twf 17973 show greater anatomical affinity with extant species of Combretum. From the Ethiopian flora, Combretum ‌aculeatum is characterized by the presence of perforated cells, C. ‌adenogonium present uniseriate rays, C. ‌rochetanium and C. ‌molle have uniseriate and included phloem a feature also observed in C. ‌adenogonium, C. ‌paniculatum and C. ‌nigriscans. C. ‌aculeatum are present uniseriate or 1-3 seriate rays, axial parenchyma is scanty paratracheal or vasicentric. No xyloanatomical data are currently available for the Ethiopian species: C. ‌contractum, C. ‌hartmanninum, C. ‌hereroroense,C. ‌capitiliflorum ‌(Friis et al. 2011) No species attribution can be given to Twf 17965 or to Twf 17973 so, they are simply attributed to Combretum sp.

In Ethiopia, Combretoxylon ‌Lemoigne has been described under several species including C. ‌desrotoris and C. sp. 3 from the Miocene (Lemoigne 1978). They differ from the Shungura Pleistocene wood by having vessels in long radial multiples. From the same deposits Combretoxylon sp. 1 is characterized by 1-2 seriate rays, whereas C. sp. has wider vessels. Combretoxylon sp. from Debre-Libanos (Beauchamp et al. 1973) and C. ‌namaensis ‌Bamford from South Africa exhibit wider vessels (Bamford 2003). In contrast, C. cf. C. ‌collinum from the Yellow Sands deposits differs from the Shungura fossil wood in lacking included phloem (Koeninger pers. comm.). Therefore, we consider that Twf 17965 and Twf 17973 both belong to Combretum without more specific precision than Combretum sp.

Ethiopia•Lower Omo Valley, Shungura Formation, Member G-29, locality P 726 sect. 19; R. Bonnefille & Jean de Heinzelin leg.; Twf 17907; Tervuren collection.

Twf 17907 is a small and poorly preserved twig measuring 1.5-2 cm in diameter with pith located at the center. It is diffuse-porous (Fig. 41A, B), growth rings indistinct. The vessels are solitary (40%) or arranged in radial multiple of two (37%), three (11%) up to six, with clusters being noticeable (Fig. 41). Their density ranges from 40-100 per mm². Mean tangential diameter of 50 µm (range 30-100 µm), vessels are thin walled. Perforation plates are simple, vessel elements are indistinct, intervessel pits crowded alternate, minute (5-6 µm) and not vestured (Fig. 41E), vessel ray pits are indistinct, tyloses are observed in vessels. Axial parenchyma is diffuse-in-aggregate (Fig. 41A, B), parenchyma strands not distinct in longitudinal section. Rays are 1-(2) seriate, they are high, heterocellular composed of procumbent and square cells mixed in the rays, they are 20-22 per mm (Fig. 43C, F); mean ray height is 150 µm Fibres are not septate (Fig. 41D). Crystals are visible in ray cells and parenchyma.

The diagnostic features of Twf 17907, including vessel solitary and in radial multiple of 2-3, 40-100 per mm², simple perforation plate, axial parenchyma apotracheal diffuse or diffuse-in-aggregate and forming very narrow bands, rays uniseriate or 2 seriate, heterocellular with mixed procumbent, square and upright cells, prismatic crystal in ray cell and parenchyma indicate affinities with extant members of the families Apocynaceae, Ebenaceae, Rubiaceae and Sapotaceae (Metcalfe & Chalk 1950; InsideWood 2004-onwards). However, the occurrence of broader rays and vasicentric tracheids in wood of Apocynaceae, Rubiaceae and Sapotaceae excludes any attribution of Twf 17907 to these families. Instead, the presence of small to medium-sized vessels occluded with tyloses, scanty paratracheal to diffuse-in-aggregate axial parenchyma, 1-3 seriate heterocellular rays, bordered intervessel pits and simple perforation plates together suggest a closer affinity with the Ebenaceae in particular Diospyros or Euclea. In Ethiopia, Euclea ‌racemosa Murray subsp.schimperi ‌(A.DC.) F. White, and E. ‌divinorum ‌Hiern are montane species with uniseriate rays. Diospyros is represented in the Ethiopian vegetation by three species. D. ‌scabra is not described in available databases, D. abyssinica ‌(Hiern) F. White is characterized by exclusively uniseriate rays. We conclude that Twf 17907 belongs to Diospyros. Since its characteristics resemble that of the Omo sample Twf 17683 from the Pliocene (Diospyros cf. mespiliformis; Table 1). However, the Pliocene sample has only uniseriate rays. Therefore, we attribute Twf 17907 to a different species, Diospyros sp. 2 (Table 2; Fig. 42).

Fossil wood close to Diospyros are documented since the late Cretaceous period under the morphotype Ebenoxylon ‌Felix with Ebenoxylon ‌ebenoides ‌(Schenk) Kräusel Kaiser from the Libyan desert (Kräusel 1939). A second species, Ebenoxylon ‌aegypticum ‌Krausel is known from in the Oligo-Miocene deposits of Egypt (Kräusel 1939).

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 742 sect. 22, Member G-29, 1.9 Ma; Jean de Heinzelin leg; Twf 17826; Tervuren collection.

Twf 17826 is not well preserved; fungal hyphae are noticed in vessel lumina. The wood displays a diffuse-porous structure (Fig. 42A, B), growth ring boundaries are indistinct. The majority of vessels are solitary (80%), with a few in radial multiples of 2 (14%) or 3 (5%); only a small proportion of clusters are visible (1%). The mean tangential diameter measures 167 µm (range 69-253 µm), 20-26 vessels per square millimeter, and the vessel wall thickness measures between 12-13 µm, perforation plates are exclusively simple, vessel elements length are short, mean 110 µm (range 90-113 µm). Intervessel-pits are crowded, alternate and vestured, measuring 8-11 µm (Fig. 42E), gum-like deposits can be observed in the vessels. Axial parenchyma is abundant, vasicentric, with up to 6 rows of aliform cells that are confluent up to 6-7 vessels, or wavy and discontinuous banded. These bands are 1-3 cells wide (27 µm) but can be up to 8 cells wide (115 µm). Strands of 1-2 and 3-4 cells can also be observed. The parenchyma lacks storied or irregular structure. The fibers diameter presents medium to mostly thick walls, without any septae or pits observed. Rays are (1)-8 seriate, composed of procumbent cells (Fig. 42D, F), and occur at a density of 5-6 per mm2 (Fig. 42C, D). Mean ray height is 430 µm (range 85-790 µm), mean ray width 50 µm (18-85 µm). Strands of crystalliferous axial parenchyma exhibit one rhomboidal crystal that distinguishes the fibers and parenchyma. Each strand consists of 10-24 chambers.

Although some diagnostic features are not clearly visible, the associated diffuse-porous wood, banded parenchyma, alternate and vestured pits, homocellular rays 1-8 seriate and prismatic crystals in fibers, clearly distinguish the fossil from Millettia ‌(Dechamps 1983) and from other members of the tribe Millettieae (Gasson et al. 2004; InsideWood 2004-onwards). Species of Millettieae consistently exhibit storied parenchyma, whereas the Omo fossil specimen Twf 17826 does not. Furthermore, Twf 17826 differs from Millettia with its wider rays (1-8 seriate) and the presence of crystals in the fibers. The closest affinities are with the genera Bussea and Burkea. However, Burkea ‌africana differs from the Twf 17826 by the absence of irregularly arranged parenchyma strands. Therefore, Bussea is considered a better match, although it does not exist in Ethiopia (Friis et al. 2011). The species of Bussea ‌occidentalis, commonly found in West Africa, exhibits only 1-3 seriate, whereas B. ‌perrieri and B. ‌sakalava are endemic to Madagascar. B. ‌massaiensis ‌(Taub.) Harms, found in East Africa, could be a possibility. But in the lack of description for that species, Twf 17826 remains identified as Bussea sp. (Fig. 42)

In Africa, several palaeontological specimens assigned to Caesalpinioxylon ‌Schenk have been described from the Pliocene. C. ‌faurei ‌Koeniguer from North Africa (Koeniguer 1973b) is characterized by uniseriate rays and septate fibers, while C. ‌tchadense ‌Koeniguer from Chad exhibits storied rays and septate fibers. C. ‌mogadaense ‌Boureau has banded parenchyma (Boureau 1950). In Northern Kenya, another Fabaceae fossil wood from the archaeological site of FwJj20, dated to 1.95 Ma, has been attributed to Schotia ‌Jacq., among the Detarioideae (Bamford 2011). This specimen is distinguished by smaller vessels, septate fibers and abundant prismatic crystals in chambered parenchyma and fibers. From the Pliocene Usno Formation in the Omo Valley, the specimen Twf 17923d related to Caesalpinia sp. shows banded parenchyma and small vessels (Jolly-Saad & Bonnefille 2023). It is clearly distinguished from the Omo sample Twf 17826 that we attribute to Bussea sp.

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 743 sect. 22, Member G-29, 1.92 Ma; Raymonde Bonnefille & Jean de Heinzelin leg.; Twf 17968; Tervuren collection.

Twf 17968 exhibits moderate preservation. The wood is diffuse-porous (Fig. 43A), with distinct growth ring boundaries characterized by a reduction in fiber diameter and marginal parenchyma bands, typically 1-2 cells wide, often accompanied by small vessels or vessel groups. Vessels are solitary (83%) or in radial multiple of 2 (17%), clusters are present, circular. Mean tangential diameter of 121 µm (range 3- 207 µm), 3-10 per mm per mm², gums and tyloses are distinct. Vessel element range is 98-231 µm, perforation plates are exclusively simple, intervessel pits alternate, 5-6 µm and vestured, vessel-ray pits are not discernible (Fig. 43E). Axial parenchyma is vasicentric enclosing vessels or group of vessels forming aliform, winged aliform to confluent 1-3 seriate tangential row, marginal bands composed of two or three cells. The marginal parenchyma is continuous with the paratracheal parenchyma; parenchyma strands of 2-4 cells are distinct (Fig. 43B). Rays are 1-3 seriate, homocellular to slightly heterocellular (Fig. 43C, D), 1-2 rows of marginal upright cells or square or upright cells, 6-10 rays per mm, mean ray height is 230 µm (range 112-632 µm) (3-44 cells), mean ray width 21 µm (range 5-18 µm). Chambered parenchyma cells with crystals up to 14 chambers and crystals in ray cells. Fibers are septate with thin wall and a diameter size between 6-11 µm.

The predominant anatomical characteristics of Twf 17968 are: mostly solitary vessels (83%) and vestured intervascular pits; axial parenchyma is paratracheal vasicentric, featuring aliform, winged aliform, and confluent patterns, with marginal bands up to 2 cells wide; rays typically 1-3 seriate and homocellular to sightly heterocellular. Prismatic crystals are present in chambered parenchyma and ray cells, and the fibers are septate. Twf 17968 was initially identified as Cathormion ‌altissimum ‌(Hook. f.) Hutch. & Dandy a morphogenus later invalidated (Gregory et al. 2009). In the Omo fossil Twf 17968, the presence of marginal bands excludes affinity with the Mimosoideae and more specifically with Cathormion, a genus of West African and not listed in the Atlas of potential vegetation of Ethiopia (Friis et al. 2011). The combination of lozenge shaped parenchyma, low radial multiples of large vessels, and prismatic crystals in the ray and parenchyma cells indicate that our described specimen (Fig. 44) rather belongs to the Fabaceae, with homocellular 1-3 seriate rays, initial/terminal axial parenchyma suggesting closer affinities to the Caesalpinoideae, Detarioideae or Papilionoideae. Vessels solitary and in multiples, simple perforation plates, vestured intervessel pits, axial parenchyma abundant, vasicentric aliform to confluent and or bands, simple fibers, homogeneous rays (mostly 1-3 seriate) are diagnostic of the Caesalpinoideae (Metcalfe & Chalk 1950; Wheeler & Baas 1992), and more specifically with genera such as Afzelia, Berlinia/isoberlinia, Cryptosepalum,Peltophorum ‌(DC.) Backer ex K. Heyne, Tessmannia, and Tamarindus. According to Müller-Stoll & Mädel (1967), parenchyma distribution is crucial for distinguishing these weakly delimited types. Afzelia and Peltophorum look similar. Septate fibers do not exist in Afzelia and Tamarindus but only in Peltophorum making it the most likely match for Twf 17968.

Among comparable fossil wood described in the literature,Caesalpinioxylon ‌Schenk, Caesalpinioxylon aff. quirogae ‌Schenk from the Miocene of Western Sahara (Koeniguer 1967) lacks septate fibers; C.faurei ‌Koeniguer has banded parenchyma and storied rays.C.moragjonesiae ‌Crawley from the Paleocene of Mali (Crawley 1988) and C.tchadense ‌Koeniguer from the Pliocene of Chad (Koeniguer 1975) both exhibit storied rays. C.mogadaense ‌Boureau from the Miocene of Algeria has uniseriate rays and no septate fibers (Boureau 1950).Pahudioxylonwelkiti ‌Lemoigne & Beauchamp, from the Miocene at Welkite (Ethiopia), is characterized by large rays (Lemoigne & Beauchamp 1972). Afzelioxylon species generally have septate fibers, and rays, axial parenchyma and vessel elements that are commonly storied (Louvet 1965). A.kilianiLouvet 1965 (Oligocene from Algeria), A.aethiopicum ‌Lemoigne, Beauchamp & Samuel from the Miocene of the upper Omo valley (Lemoigne et al. 1974) and A.furoni ‌Koeniguer from the Paleocene from Sessao (Niger) lack septate fibers. Caesalpinioxylon typically has short to medium vessel element lengths, mainly solitary vessels, axial parenchyma confluent and banded, uniseriate rays that are heterocellular and usually storied (Müller-Stoll & Mädel 1967). Copaiferoxylon has regular axial canals. Pterogynoxylon ‌(Müller-Stoll & Mädel 1967) has prismatic crystals in rays and storied rays and axial parenchyma. Cassinium has rays 1-4 (mostly 3-4) seriate, which are homocellular to weakly heterocellular and occasionally storied (Prakash 1973). These comparisons highlight that, although the Shungura fossil wood shares some features with these taxa, it also exhibits key differences, particularly regarding the presence/absence of storied structures, septate fibers, and ray composition. Twf 17968 remains attributed to Peltophorum sp. (Fig. 43; Table 2).

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 742 sect. 22, Member G-29, 1.92 Ma; Jean de Heinzelin leg.; Twf 17825; Tervuren collection.

Twf 17825 has a diameter ranging from 1.8 to 2.4 cm and shows minor compression. Preservation quality is good or fairly good in transverse sections, but poor in the longitudinal plane. The thin sections of this specimen are too thick for precise identification of cells and tissues. Abundant fungal hyphae are distinct in the vessel lumina (Fig. 44C), while the peripheral region displays an amorphous structure. Possibly, Twf 17825 may have been degraded before mineralization took place.

The wood is diffuse-porous, no apparent growth rings. Vessels are primarily solitary, with a round or oval shape, although some are in radial multiples of 3-4, with 8-12 vessels per square millimetre. The mean tangential diameter is 250 µm (with a range of 57-350 µm), the perforation is simple. In addition, dark deposits and abundant fungi hyphae can be found in the vessels, with small intervessel pits (<4 µm) that are possibly vestured and alternate-scalariform in shape. Axial parenchyma is scanty paratracheal. Rays are 1-3 seriate, predominantly 2 seriate composed of procumbent cells with a single row of upright cell (Fig. 44D), 8-10 per mm, ray range height is 350 µm (range 153-552 µm) (8-33 cells), mean ray width is 35 µm (18-51 µm). Fibres show thin walls and likely are non septate. Crystals are present in non-chambered parenchyma.

Twf 17825 is characterized by predominant solitary large vessels, vestured intervessel pits, rays composed of procumbent cells. Diagnosis of Twf 17825 is challenging due to the poor preservation of the longitudinal sections. It shares similarities with some taxa of the Fabaceae or Apocynaceae.

Ethiopia•Lower Omo Valley, Shungura Formation, Member G-29, locality P 743 sect. 22 coupe A; Jean de Heinzelin leg.; Twf 17625; Tervuren collection.

Twf 17625 is poorly preserved with marks of compression. The wood is diffuse-porous, growth rings indistinct. Vessels are round to oval in shape, solitary (49%) or in radial lines of 2 (30%), 3 (11%), 4 (8%), 5 (1%), 4-9 vessels per mm² (Fig. 46A, B), mean tangential diameter is 102 µm (range 60-150 µm). Vessel elements are short, mean 280 µm (range 250-300 µm), perforation simple, horizontal, intervessel pits are 5-6 µm wide, sometimes coalescent to slightly scalariform (Fig. 45), vessel-ray pits are not discernible. Gum and black deposits are distinct in vessels; axial parenchyma vasicentric, banded with 3 or 4 rows of cells, strands of 2-4 and 5-8 cells; sheath cells are visible. Rays are 1-7 seriate heterocellular, composed of procumbent cells with one or 2-4 rows of square upright cells (Fig. 45C-E). Mean ray height is 1000 µm (range 600-1552 µm), ray width is 130 µm (range 99-137 µm). Uniseriate rays are rare and exclusively composed of square and upright cells. Fibers are not septate. Prismatic crystals are visible in ray cells.

This wood shows characteristics such as solitary or radial grouped vessels, heterocellular pluriseriate rays, narrow bands of 1-3 cells wide, forming an axial parenchyma arranged in a reticulate pattern, the rays as storied cells, sheath cells, intervessel pits medium, coalescent or scalariform. These traits indicate that this wood has the closest affinities with some extant Malvaceae-Sterculoideae genera. Interestingly, Eribroma and Tarrietia have fewer vessels per mm² compared to the Shungura fossil specimen, Pterigota has larger parenchyma bands, whereas Cola species possess silica bodies in their ray cells. Some similarities exist between Twf 17625 and Sterculia, the only genus from Ethiopia, known under five species (Vollensen 1995c). S. ‌setigera differs from Twf 17625, with less vessels per mm² (< 5) and coalescent or scalariform pits. Since we have no description of other species, Twf 17625 is designed as Sterculia sp. (Table 2; Fig. 45).

In North Africa, Sterculiniumfreulonii ‌Boureau from post-Eocene deposits (Bourreau 1957), Sterculioxylonaegyptiacum ‌(Unger) Kräusel (Louvet 1969) from Eocene-Oligocene have no storied structures.

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 769 sect. 22, Member G-29, 1.92 Ma; Jean de Heinzelin leg.; Twf 17725; Tervuren collection.

Twf 17725 exhibits a black color and very poor preservation. It is diffuse-porous, with the absence of growth rings (Fig. 46A). Vessels are mostly solitary or in radial multiple up to 4, mean tangential diameter is 230 µm (range 92-400 µm), with a density of 4-6 per square millimeter, tyloses are present. Vessel member length range is 100-360 µm with simple perforation plates. Vessel pits are alternate, 9-10 µm wide (Fig. 46E). Two types of axial parenchyma can be distinguished, one vasicentric, surrounding the vessels, the second forming axial parenchyma large bands with 3 up to 7 cells high (Fig. 46A). Parenchyma strands are composed of 5-8 cells; Rays are 1-8 seriate (Fig. 46C, D), mean ray height is 800 µm (range 400 µm-1000) and width varies from 34 to 52 µm. Rays are heterocellular, composed of procumbent cells, with one or two rows of upright/square cells in the marginal Twf 17707 cells. Prismatic crystals are present in the terminal cells; fibers non-septate. Lacticifer canals are present (Fig. 46A-F). Prismatic crystals occur in the parenchyma and in ray cells.

The fossil is characterized by diffuse-porous wood composed of small to medium-sized vessels, occurring singly or in short radial multiples, exclusively simple perforation plates and tyloses in vessels. It also exhibits banded axial parenchyma, typically 3- to 7-seriate, that form undulating, anastomosed lines, along with heterocellular 1 to 8-seriate rays. These characteristics closely resemble those of Ficus ‌(Dechamps 1983), notably wider rays (more than four cells wide) and regular parenchyma bands. In Ethiopia there are over 12 species of Ficus ‌(Friis et al. 2011). We can exclude two of them. F. capensis ‌Thunb. (syn.: F. ‌sur ‌Forssk) has middle size vessels, large parenchyma bands of more than 15 cells and large rays. F. ‌vallis-choudae has middle to large vessels, parenchyma bands made of 3 to 12 cells and 1 to 9 seriate rays, therefore larger than those of Twf 17725.

In Africa, several fossil wood samples have been related to Ficus. In Ethiopia, the Late Cretaceous/Eocene Ficoxylon sp. has no sufficient description (Beauchamp et al. 1973) to enable a meaningful comparison with our Pleistocene specimen. Ficoxylon ‌cretaceum(Schenk 1883) from a lower Miocene site (Lemoigne et al. 1974) is clearly distinguished from our studied sample Twf 17725 by its 1-3 seriate rays. Ficoxylon ‌blanckenhornii ‌Kräusel, from the Wondo Miocene site (Lemoigne et al. 1974) is 3-6 seriate. Ficoxylon sp. from the Pliocene (4.4 Ma) at Middle Awash differs from the Shungura fossil wood with 1-6 seriate rays (Jolly-Saad et al. 2010). Ficus sp. also from Middle Awash is 1-5 seriate (Jolly-Saad & Bonnefille 2012: pl. 5). Ficus sp. from the Lower Omo Valley (Dechamps & Bande 1994) has large vessels (140 à 450 µm), rays 2-5 seriate, large band of parenchyma (up to 14 cells each). Elsewhere, in Africa, many fossil woods have been attributed to several species of Ficoxylon. F. ‌cretaceum come from the Cretaceous (Boureau 1949a, b; Dupéron-Laudoueneix & Dupéron 1995; Kräusel 1939), F. ‌blanckenhornii from the Oligocene and early Miocene of Egypt (Kräusel 1939) Sudanese Sahara (Boureau 1949b) and the Oligocene of Tunisia (Fessler-Vrolant 1979). From the Oligocene in Libya, Ficoxylon ‌guettarense has rays of 1 or 3 cells but intravascular pittings less than 4 µm in size (Fessler-Vrolant 1972). Ficoxylon ‌melahense, related to Asian species of Ficus ‌(Louvet 1971) is clearly distinguished from the studied fossil specimen Twf 17725 by the occurrence of storied parenchyma. The Omo fossil sample species with narrow rays exhibits a similar undulating pattern as Ficoxylon ‌guettarense ‌(Fessler-Vrolant 1972). However, Twf 17725 differs in having less dense vessels (4-6/mm²) and denser rays (12-16/mm²). It is related to Ficus. Differences in anatomical characteristics of Twf 17725 (Fig. 47) and Twf 17928 (Fig. 38), mean it is likely that they represent two distinct species, respectively Ficus sp. 2 and Ficus sp. 1. (Table 2). The anatomical characters and measurements of the two Pleistocene Ficus are clearly distinct from those of the two species previously described in the Pliocene at Middle Awash, in Ethiopia (Jolly-Saad et al. 2010; Jolly-Saad & Bonnefille 2012) as reported in Table 5.

Ethiopia•Lower Omo Valley, Shungura Formation, Member G-29, locality P 743 C sect. 22; Jean de Heinzelin leg; Twf 17629; Tervuren collection.

Twf 17629 is not very well preserved. Wood is diffuse-porous, growth ring boundaries absent. Vessels are exclusively solitary, 20-22 vessels per mm² (Fig. 47A). Mean tangential diameter of vessels is 43 µm (range 10-81 µm), vessel walls thick, mean vessel elements 170 µm (range 160-195 µm), perforation plates simple. Intervessels pits alternate, 3-4 µm wide and vestured. Vessels-ray pits are similar to vascular pits. Axial parenchyma diffuse-aggregates (Fig. 47B), one row of cells. Perforate ray cells are visible. Rays are 1-4 (5) seriate (Fig. 47C, D), mean ray height is 350 µm (range 80-621 µm), a few up to 1.2 mm, mean ray width is 90 µm (range 58-103 µm). Uniseriate rays are exclusively composed of upright cells. There are 4-5 per sq mm, they are composed of square and upright cells mixed throughout the rays (Fig. 47F). Sheath cells are distinct (Fig. 47D, E). Fibre tracheids are visible. Fibres are medium to thick walled. Inclusions are visible in square and upright cells.

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 743 C sect. 22, Member G-29, 1.92 Ma; Jean de Heinzelin leg; Twf 17630; Tervuren collection.

Longitudinal section is not correctly preserved. Wood diffuse-porous, growth rings absent. Vessels are solitary, round or oval in shape, few clusters are present (1%). Mean tangential diameter of 50 µm, range (20-75 µm). Vessel wall is 8 µm thick. 20-35 vessels per mm². Perforation plates exclusively simple; vessel elements are short, vessel-pits crowded alternate and vestured, 3-4 µm. Fibers diameter is medium to mostly thick walled. Fibres are septae. No pits observed. Parenchyma diffuse-in-aggregates, one row, parenchyma is not storied. Strands of parenchyma cells are indistinct. Rays are 1-5-seriate, heterocellular composed of procumbent cells. 5-6 per mm, mean ray height is 450 µm (range 80-921 µm), few up to 1.2 mm, mean ray width is 90 µm (range 60-110 µm). Uniseriate rays are composed of upright cells.

The most diagnostic features of Twf 17629 and Twf 17630 are: small vessels, intervessels pits vestured, axial parenchyma diffuse-aggregates, wide and long heterocellular rays, perforated ray cells which resemble to those of extant Ochnaceae and more specifically to Ochna as proposed by Dechamps.

Twf 17629 and Twf 17630 attributed to Ochna and dated 1.92 Ma (Fig. 48). They represent the only fossil record of the Ochnaceae from Ethiopia or elsewhere in Africa. Distinct anatomical structures from that of sample Twf 17949A in F3-2, dated 2.3 Ma, and attributed to Ochna sp. 1 (Fig. 23; Table 2) indicate that three distinct species of Ochna may have existed in the Lower Omo valley between 2.3 to 1.9 Ma. Four species are described in the Flora of Ethiopia (Friis et al. 2011; Vollensen 1995c). Ochna ‌bracteosa is from the transitional rainforest; O. ‌inermis ‌Forssk. Schweinf ex. Penzig from the Acacia-Commiphora woodland and bushland (500 to 1900 m). O. leucophlocos Hochst. ex. A. Rich. 1847, and O. ‌schweinfurthiana ‌F. Hoffin are both from the Combretum-Terminalia woodland. Unfortunately, no xyloanatomical data are available for any of these species.

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 743 C sect. 22; Member G-29, 1.92 Ma; Jean de Heinzelin leg; Twf 17636; Tervuren collection.

Twf 17636 exhibit relatively good preservation. The wood is diffuse-porous and lacks growth rings. The majority of vessel distribution is solitary (88%) with a minority occurrence in radial multiples of 2 (11%) and 3 (1%), organized in an oblique and dendritic pattern (Fig. 48A, B). The vessels are oval in shape and outline, the mean tangential diameter is 31 µm with a range of 14 µm to 57 µm, and a density of 25-40 per mm². Perforations are solely horizontal and uncomplicated; vessel elements and intervessel pits are not visible. Axial parenchyma is diffuse-in-aggregates in row of 2 or 3 cells, lacking a clear distinction (Fig. 48B, E). The parenchyma strands are not distinct in longitudinal section. The rays are predominantly uniseriate, biseriate rays rarely occurring (Fig. 48C, D). They consist of mixed square and upright cells observed at a frequency of 10-12 per mm2, mean ray height is 500 µm (range 330-598 µm) (14-27 cells), a few exceed 1mm. Mean ray width is 14 µm (range 13-15 µm) with fibers possessing thick walls (5 µm) and a diameter ranging from 11 to 20 µm. No pits or septae have been observed, while prismatic crystals are distinct in ray cells.

The combination of vessels in an oblique dendritic pattern, narrow heterocellular rays, uniseriate sometimes biseriate and chambered crystalliferous parenchyma, are not found in the genera Manniophyton or Macaranga (Euphorbiaceae) as suggested by Dechamps (1983). In the Ebenaceae family, only Diospyros ‌abyssinica displays vessels in a diagonal pattern, but axial parenchyma shows diffuse-in-aggregates cells in one, 2 or 3 rows. Fossil wood sample Twf 17636 displays resemblances to the Sapotaceae family. Today, Sapotaceae are found in Ethiopia, especially in the highland rainforest and riverine forests (Friis 2003; Friis et al. 1982). The family consists of five genera, namely Mimusops L., Vitellaria ‌Gaertn. f., Manilkara ‌Adans, Sideroxylon L., Pouteria ‌Aublet. As pointed out by Prakash et al. 1982), the wood anatomy of the Sapotaceae is quite uniform, with considerable overlap between the genera (Wheeler et al. 2007). Our Shungura sample can only be attributed to the Sapotaceae family without further generic attribution (Table 2; Fig. 48).

Five fossil “Sapotoxylon” morphotypes have been described from the Tertiary in Ethiopia, “Sapotoxylon ‌aethiopicum” ‌(Lemoigne et al. 1974), from the Miocene at Debre Sina, has 1-3 seriate rays with sheath cells. S. ‌lecomtedoxiodes ‌(Lemoigne, 1978), from the Miocene of Welkite, has considerably wider vessels (150-250 µm). S. ‌multiporosum from the Mio-Pliocene of the Blue Nile Valley has heterocellular and 1-3 seriate rays, a higher vessel density (60-120 per mm²), and more rays per mm2 (18-20) (Prakash et al. 1982). At Fejej (tree 18) features of the species Sapotoxylon sp. 1, has large vessels (132 µm) with a radial to oblique pattern, 2-3 seriate rays, a body of procumbent cells with long uniseriate margins of upright cells, and inclusions. Solitary prismatic crystals are commonly found within chambered axial parenchyma in a series of 4 to more than 12 chambers (Ref). Twf 17636 differs from all these fossil specimens.

Ethiopia•Lower Omo Valley, Shungura Formation, locality non available, sect. 22, Member G-29, 1.92 Ma; Frank Brown & Jean de Heinzelin leg; Twf 17966; Tervuren collection.

The transverse and radial sections are fairly well preserved, while the longitudinal and tangential sections are poorly preserved. Diagnostic features are only distinct in limited areas of each section. The studied sample is a small stem with a central cylinder of parenchyma. The wood is diffuse-porous with distinct growth rings (Fig. 49A). Vessels are mostly solitary (84%) and few in radial multiples of 2 (11%), 3 (5%) (Fig. 49B). Mean tangential diameter of 80 µm, range 65-100 µm, 16-30 vessels per mm². Perforation plates are exclusively simple, inter-vessel pits not distinct, vessel-rays pits large and bordered (Fig. 49G). Axial parenchyma is scanty paratracheal and in marginal bands, initial/final parenchyma (one row), strands of parenchyma not seen in longitudinal section. Rays are uniseriate, few of them are biseriate on one row, composed of procumbent cells with one row of upright cells, 10-12 per mm2, mean ray height range is 240 µm (range 73-312 µm) (5-28 cells), mean ray width is 11 µm (range 10-12 µm) (Fig. 49C, D). Fibers are thick-walled and septate. Crystals are distinct in ray cells. Fibers are thick to mostly very thick walled, not clearly distinct in tangential view.

The fossil is characterized by diffuse-porous wood with distinct growth rings. Vessels occur singly or in radial multiples of 2 or 3, featuring exclusively simple perforation plates. Axial parenchyma is scanty paratracheal, forming marginal bands and initial/final parenchyma. The general wood anatomy of the Shungura sample closely resembles that of the fossil genus Terminalioxylon ‌(Mädel-Angeliewa & Müller-Stoll 1973), but it has small vessels with well-defined pits rather than vestured pits. This observation excludes affinities with Terminalia, as the presence of vestured pits is one of the diagnostic features of this genus (Van Vliet 1979). The Twf 17966 fossil specimen more likely corresponds to the structure of the family Sapindaceae ‌(Klaassen 1999).

Micro-anatomical structure of Twf 17966 is near that of the morphotype Sapindoxylon ‌Kräusel, described from the Cretaceous to the Plio-Pleistocene, in Africa as well as in Ethiopia. Sapindoxylon sp. Beauchamp (Cretaceous-Eocene) has large rays (Beauchamp et al. 1973). S. ‌almelai ‌Koeniguer (Mio-Pliocene Sahara) has more bigger vessels than Twf 17966 (Koeniguer 1967). S. ‌haileselassiei ‌Lemoigne (Oligo-Miocene from Ethiopia) has 1-3 seriate rays, vasicentric parenchyma and wider vessels in radial multiple up 15 vessels (Lemoigne1970). S. (Blighioxylon) koholense ‌Koeniguer (Algeria) and S. sp. Koeniguer (Libya) have 1-3 seriate rays, large vessels and less vessels density than the Omo fossil and scanty paratracheal parenchyma (Koeniguer 1967, 1972). S. ‌mbaense ‌Koeniguer (Eocene, Senegal) has uniseriate rays and scanty paratracheal parenchyma (Koeniguer 1973a). S. ‌stromeri ‌Kräusel (Oligo-Miocene from Egypt) has vasicentric parenchyma, wider vessels in radial multiple up 15 vessels, septate fibers and prismatic crystals in rays and parenchyma, two features indistinct in Twf 17966. A fossil wood placed in Sapindoxylon, related to the type specimen S. ‌stromeri has been described from the site Fwjj 14, dated 1.56 to 1.36 Ma at Ileret, East Turkana, Kenya. It differs from Twf 17966 by having bigger vessels, smaller radial multiples, exclusively uniseriate rays and parenchyma that is either rare or sparse paratracheal (Bamford 2017). In conclusion, Twf 17666 is attributed to the Sapindaceae without any generic precision (Table 2; Fig. 50).

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 742b sect. 22, Member G-29, 1.92 Ma; Jean de Heinzelin leg; Twf 17780 (Fig. 50), Twf 17987; Tervuren collection.

Both specimens consist of small twigs that contain a central cylinder of parenchyma. Their three thin sections are well preserved with similar anatomical structures. The description and illustrations (Fig. 50) are from Twf 17780. The wood is diffuse-porous with clear growth ring boundaries, marked by the presence of initial or terminal parenchyma. Vessels exist either in solitary formation (67%) or arranged in radial multiple of 2 (20%), 3 (8%), 4 (3%), or 6 (2%) (Fig. 50A). The tangential vessel diameter mean is 76 µm (range 27-90 µm), 14-20 vessels per mm². The vessel wall is thick measuring 8-9 µm (Fig. 49F). Vessel element length range is 176 µm (200-350 µm). Helical thickenings are present on few vessel walls. Intervessel pits are round to polygonal, and 3-4 µm wide, while perforation plates are simple and horizontal. Gum deposits are noticeable in vessels, but vessel-ray pits were not observed. Axial parenchyma is scanty paratracheal to vasicentric with 1-2 row of terminal/initial parenchyma, occasionally diffuse (Fig. 50B). Prismatic crystals are distinct in chambered parenchyma. Rays are mostly uniseriate but some are locally biseriate on one or two rows, mean ray height is 100 µm (range 45-195 µm), up to 12 cells, mean ray width is 15 µm (range 11 to 16 µm) (Fig. 50C, D). They are 12 or more rays per mm2. Composed of mixed procumbent, square and upright cells and one row of marginal upright cells, the rays are heterocellular and have dark deposits. Fibers seem aligned, their diameter is between 8-18 µm, they have also thick walls and are not septate. Crystals are distinct in ray cells and in chambered parenchyma.

The combination of solitary vessels and in radial multiple, simple perforation plates, narrow tangential diameter of vessels, scanty paratracheal and seemingly banded parenchyma, narrow non-storied rays, and chambered crystalliferous parenchyma occurs in woods of Combretaceae, Fabaceae, Rutaceae, and Sapindaceae. Vessel pits are usually larger in the Combretaceae, Fabaceae have vestured pits. The affinity of Twf 17780 and Twf 17987 is more likely with the Sapindaceae ‌(Klaassen 1999).

In Ethiopia, the Sapindaceae comprise several genera (Friis et al. 2011; Vollensen 1989). Allophylus ‌africanus ‌P. Beauv.,A. ‌abyssinicus ‌(Hochst.) Radlk. and Haplocoelum ‌Radlk. exhibit an absence or scarcity of axial parenchyma. No xyloanatomical data are available for Bottegoa ‌insignis ‌Chiov.Cardiospermum ‌corindum L. and C. ‌halicacabum L. have larger raysDeinbollia ‌kilimandscharica ‌Taub. and Zanha ‌golungensis ‌Hiern. possess a greater amount of axial parenchyma than Twf 17780. Pappea ‌capensis displays a higher density of vessels per mm² and a greater quantity of parenchyma as well. Dodonaea and Lecaniodiscus are the most closely related modern relatives. Septate fibers are not distinctive of Dodonaea. Twf 17780 shows similarities with Lecaniodiscus ‌(Metcalfe & Chalk 1950). With uniseriate rays, parenchyma initial/terminal and septate fibers, both samples Twf 17780 and Twf 17987 correspond to Lecaniodiscus sp. (Klaassen 1999) (Table 2; Fig. 50). They do not fit description of any Sapindoxylon morphotypes as discussed during description of Twf 17966 attributed to Sapindaceae.

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 743 A sect. 29, Member G-29, 1.92 Ma; Jean de Heinzelin leg; Twf 17624; Tervuren collection.

The description of Twf 17624 cannot be achieved due to insufficient preservation. The transverse section is not preserved. In longitudinal tangential section, rays are 1-2 seriate, featuring distinct crystals. The fossil wood was mentioned as Diospyros ‌(Dechamps 1983), but not seem acceptable with regard to poorly preserved transverse section.

Ethiopia•Lower Omo Valley, Shungura Formation, locality P 742 sect. 22, Member G-29, 1.92 Ma; Jean de Heinzelin leg; Twf 17824; Tervuren collection.

Twf 17824 has undergone severe degradation in all three sections, likely before mineralization, leading to an amorphous structure. Some vessels display evident fungal hyphae. The wood is diffuse- porous and growth rings are absent. Vessels are solitary round or oval in shape. Mean tangential diameter of 45 µm (range 35-55 µm). Vessel walls are thick, 20-35 vessels per mm². Perforation plates are exclusively simple; vessel elements are short, vessel pits are 4-5 µm wide. It is not possible to see whether they are vestured or not. Rays-pits are not distinct. Parenchyma is indistinct. Rays are 1-5 seriate and heterocellular. Characteristics of the fiber not visible.

Twf 17824 was initially attributed to Ochna ‌(Dechamps 1983). However, it lacks the diffuse-in-aggregate parenchyma characteristic of Ochna species that would be necessary for a conclusive identification of this specimen.

Ethiopia•Lower Omo Valley, Shungura Formation, locality L 618 sect. 4, Member G-15, 2.04 Ma; American Staff leg; Twf 17612; Tervuren collection.

Twf 17612 displays very poor preservation, lacking several tangential features. Its black color suggests similarity to charred material. Degradation most probably occurred before fossilization. Notably, no evidence of fungi is observed. The wood is diffuse porous, growth rings are distinctly marked by the reduction of fibers diameters. Vessels are mostly solitary or in radial multiple of 2 or 3 up to 6. Mean vessels diameters vary little from 180-to 200 µm. Vessels are 10 per mm². Abundant gum and black deposits are visible in vessel lumina; vessels element high not distinct, vessel pits and ray pits are indistinct. Axial parenchyma in narrow apotracheal bands combined with scanty paratracheal parenchyma. The tangential section is very poorly preserved, few features are visible: rays are wide, composed of large cells, pluriseriate and heterocellular, sheath cells are distinct and are heterocellular, thick-walled fibers.

Twf 17612 was previously assigned to Landolphia (Apocynaceae) (Dechamps 1983), yet micro-anatomical structures are severely degraded. Nevertheless, the observed characteristics do not support an attribution to Landolphia, that typically exhibits mostly solitary vessels (90%), lacks deposits in vessels, and possesses 1-3 seriate rays. Twf 17612 remains an unidentified dicotyledonous wood.

Ethiopia•Lower Omo Valley, Shungura Formation, locality Kalam road, sect. 19, Member J-2, 1.70 Ma; Jean de Heinzelin leg; Twf 17986; Tervuren collection.

Twf 17986 is a small twig measuring 1 × 2 cm in diameter with pith located at the centre. It is diffuse-porous, growth rings indistinct. The vessels are solitary (40%) or arranged in radial multiple of two (37%), three (11%) up to six (Fig. 51A, B). Their density ranges from 40 to 60 per mm². Mean tangential diameter is 70 µm (range 30-95 µm). Vessels are thin walled, perforation plates simple, vessel elements indistinct, vessel-pits crowded alternate, minute (5-6 µm) and not vestured (Fig. 51A-E), vessel ray pits indistinct, axial parenchyma is diffuse-in-aggregate very narrow bands (Fig. 51B). Parenchyma strands is not seen in longitudinal section. (Fig. 51G), Rays mostly uniseriate, becoming locally biseriate and high (more 1mm height), heterocellular composed of procumbent and square cells mixed in the rays. Rays width averages 30 µm (range 20-35 µm), and density of 20-22 rays per mm (Fig. 52C). Crystals are visible in ray cells and in parenchyma; fibers are not septate.

The diagnostic features of Twf 17986, including that of vessels, 1-(2) rays, perforation plate, axial parenchyma and prismatic crystals in ray cells and in parenchyma, altogether indicate affinity with extant members of Ebenaceae such as Diospyros. However, it differs from Twf 17683 from Member C, dated 2.62 Ma (Fig. 15), which has only uniseriate rays and was attributed to Diospyros ‌mespiliformis (Table 1). Twf 17986 from Member J looks more similar to Twf 17907, dated 1.92 Ma, from Member G. (Fig. 42), and indicated Diospyros sp. 2 (Table 2).

Ethiopia•Lower Omo Valley, Shungura Formation, locality Kalam road, sect. 19, Member J-2, 1.7 Ma; Jean de Heinzelin leg; Twf 17601-Twf 17604, Twf 17985, Tervuren collection.

Five samples, Twf 17601 to Twf 17604 and Twf 17985, were re-examined in this study among the seven fossil samples collected at the same locality and previously reported as a single taxon, Staeganotaenoxylon ‌araliacea ‌(Dechamps 1977). In this study, we provide description of Twf 17601 illustrated in Fig. 52 and identified as Salvadora ‌persica. All other examined samples show the same anatomical characteristics and are therefore attributed to the same taxon.

The preservation of Twf 17601, both in transversal and tangential sections is quite good with the exception of the radial section which is not perfectly preserved. Fungi are present. The wood is diffuse-porous, growth rings boundaries present. Vessels are solitary or in groups, few in radial multiple of 2-4, or group in irregular clusters. Vessels show two distinct diameter classes; mean tangential diameter of the larger and smaller size 140 µm (range 31-240 µm). There are few vessels per mm² (3-5) (Fig. 52A, B). Perforation plates exclusively simple, vessel pits are simple, average diameter is 4-5 µm and not vestured (Fig. 52F). Vessel wall is thick, brownish gum-like deposits present. Vessel elements length is short, less than 350 µm. Vessel-ray pits with distinct borders similar to vessels pits. Included phloem is visible. Fibers have thick-wall. Axial parenchyma is paratracheal varying from few cells to vasicentric and rarely confluent. Fusiform or two cells per parenchyma strands and storied. Rays up to 1-3 (4) seriate, uniseriate are few, they are heterocellular composed of mixed procumbent square and upright cells or exclusively composed of square and upright cells (Fig. 52G). They are not storied; 5-10 per mm. height range 86-456 µm and 14-51 µm wide. Prismatic crystals are abundant and located in ray cells and in chambered parenchyma (Fig. 52).

Large and short vessels elements, included phloem in concentric rows (interxylary phloem sensus Carlquist 2002), prismatic crystals and no radial canals, differ from the Apiaceae family and exclude an attribution to Staeganotaenia (InsideWood 2004-onwards; Oskolski et al. 2010), notably Staeganotaenoxylon ‌araliacea inferred by Dechamps (1977). Fossil samples have affinity with Asclepiadaceae, Menispermaceae and Salvadoraceae. Cocculus in the Menispermaceae has higher and wider rays and exclusively solitary vessels. Lepadenia, a desert shrub in the Asclepiadaceae, has larger rays up 20 cells wide and diffuse phloem. The Twf 17601 wood is similar to the Salvadoraceae including three genera in East Africa Salvadora, Dobera and Azima ‌(Verdcourt 1989). Azima ‌tetracantha has smaller vessel diameter, larger rays and axial parenchyma in bands, and does not exist in Ethiopia. There is currently a lack of information regarding the microanatomical characteristics of Dobera. In the Lower Omo Valley, fossil wood samples similar with Salvadora (Metcalfe & Chalk 1950; Carlquist 2002), represented the earliest fossil wood record from Ethiopia. However, the pollen has been found since 2.8-2.5 Ma (Bonnefille 1976b). The new identification of this genus known through a unique species Salvadora ‌persica agrees with modern habitat of the corresponding trees in the borders of seasonally dry rivers and streams in the subdesertic region of Ethiopia today.