New chirotherioid traces
Des traces chirothérioïdes
The stratigraphic study of the Permian and Triassic series of the Argana basin was made by Roch (
Recently, since the 2000s, the first two authors of this work found other footprint sites and gathered new traces during their sedimentological studies of the Argana Basin and neighbouring Permian and Triassic Formations of High Atlas Mountains ( to replace them within their geological and stratigraphic contexts; to describe the tracks themselves; to propose a chronological attribution based on a comparison with European Permian-Triassic series.
Because of numerous uses of the lithostratigraphic term Formation and Member, these will be replaced by the abbreviations Fm and Mb.
The track site of Iggui Aouglef is located about 50 km to the south of Imin’ Tanout, 8 km SSW of Timezgadiwine, and 2 km south of Irerhi village, along the Assif Aït Messaoud (
In Iggui Aouglef locality, the Triassic succession is divided into the unit T3 and the overlying unit T4 (Agelgal Mb) (
The upper part of the T3 section consists of conglomerates composed of low-angle trough cross-stratification and planar cross-stratification grading upward to horizontal lamination. This association of facies characterizes bedload deposits of gravelly braided river system.
The footprint site is located at the base of a little cliff (
The following abbreviations will be P and M = pes and manus traces often named only pes or manus, CPM = associated pes-manus; I, II, III, IV, V: digits numbering; L and W = footprint length and width; LD and WD = I–IV part length and width; LP and LM = pes and manus length, Q = cross-axis angle in degrees = angle between the metapodial-phalangeal axis and the long axis of the footprint (see
Unlike the
As a whole, this morphological organisation characterizes the ichnogenera
The pes trace dimensions are as follows: L × W = 136 × 48 mm; LD × WD = 80 × 48 mm; I–IV lengths successively equal to 38, 56, 69, 77 mm; cross-axis angle Q = 68°; angle III–V = 40°. The whole is therefore lacertoid in aspect with toes close to each other (angle I–IV = 15°). They are ended by rather strong claws directed towards the footprint inside. An oblong metatarsal mark without the digit V is only present at the back of the I–IV digital part.
The manus is located to 97 mm ahead of the pes. The digit IV is not visible. It seems to be torn off, or its trace was erased by the later passage of another animal which made a print covering partially the preceding footprint. Digits are ended by short claws. II and III are rather broad and the first (I) is present only by the claw mark; recorded dimensions are: L × W = 65 × ? 40 mm; II and III are subparallel, with III = 47 mm, II = 41 mm; digito-metacarpal pad V = 37 mm; Q = 75°, III–V angIe = 50°.
Longer than broad, it is a pes trace of which the digital lengths decrease from IV to I digits. Q is low: 60° and the angle III–V = 40°. L × W must be close to 135 × 70 mm.
It is made of two consecutive couples P1–M1 and P2–M2 (
The I–IV part is complete only in P1 where it appears paraxonic, broader than long, with LD × WD = 79 × 93 mm. It is extended backwards by the quadrangular toe V, without claw, which comes from a broad triangular to ovoid sole representing the metatarsal pad print.
Based on P1, L × W = 170 × 91 mm and digital lengths, without claws, are as follows: I = 65, II = 75, III = 70, IV = 59 mm (II > III > I > IV). This order is the same for P2 and P4. The II is thus the longest, a few millimeters longer than the III, and the IV is the smallest. The length of V is respectively 39, 28 and 11 mm for P1, P2 and P4. The pes length mean is 161 mm. The P1 trace is the best preserved; its surface is covered by transversal or oblique furrows. Those of the internal border partly correspond to a slight autopodium skid. The others are cutaneous folds and round-scale band traces which are quite visible on the toe I and a part of the II (
The M1 and M2 traces are located at 156 and 180 mm ahead of their respective pes. They show a digitigrad support. On M1, the I–IV part is as long as broad (LD × WD = 62 × 54 mm). The digits IV–II appear there broad, right, a little divergent from each other (angle IV–II = 9°), clawed and enough strong, unlike the I which is thin and not very visible because of it is stuck against the II. The digital lengths are: I = ? 29, II = 45, III = 57, IV = 50 mm; III is thus the longest with III > IV > II > I. The V trace is not distinguished from those of metacarpals. This V whole is located back to the I–IV part. It is 43 mm long and the angle III–V is 55°. M1 is as long as broad (L × W = 77 × 74 mm). The M2 trace shows the same organisation and dimensions as M1: L = 82 mm; LD × WD = 62 × 60 mm; I = ? 35, II = 48, III = 57, IV = 49 mm. The little, thin digit I is not clearly marked. V is the partial metapodium trace, not clearly readable because of a print superposition. Angle II–IV = 12°.
These footprints seem isolated on the surface. Among the best preserved, we distinguished two CPM: 9 and 1 FM (
Several chirotherioid ichnospecies were mentioned in the Lower and Middle Triassic of the USA (lower part of the Moenkopi Fm (
A comparison of the 11 FM footprints with the various ichnospecies described in the formations quoted above, shows that they more resemble the ichnospecies
We report with doubt to this ichnogenus the 2 FM pes which is not entirely visible
In addition to
Although the trackway n°1 footprints show II–III digital lengths virtually subequal, they cannot be assigned to
The pes of the trackway n°1 was also compared to that of
In the absence of sufficient measurement series for
From the two Fl/F2 graphs, P1 of the trackway and one
The 1 and 7 FM pes prints have subequal digits II–III, with a slight prevalence for the III, a characteristic favourable to its attribution to
Following a mean and variance statistical comparison, the 9 and 10 FM pes (
The osteological interpretation of
The sedimentologic characters of the beds bearing the footprints level are indicative of an alluvial plain under the influence of alluvial fan inputs. As it was suggested, this environment was therefore inhabited by a tetrapod community dominated by Archosaurian Crurotarsi. The measured orientation of their traces in the Iggui Aouglef site indicates that animals walked west-east in both directions.
Until now the unit T3 (Tanameurt Mb) of the Timezgadiwine Fm was only tentatively referred to the Triassic. It overlies unconformably the unit T2 (Tourbihine Mb) of the Ikakern Fm, assigned to the Upper Permian thanks to vertebrate remains (
Any of the ichnospecies described in the Middle Triassic of France (Anisian-Ladinian “Grès inférieurs” Fm) (
The Iggui Aouglef ichnites are represented by
According to the closeness of the aforesaid footprints with Lower Triassic ichnospecies, and the relative archaic pes bony structure of the
This study was led in the framework of collaborative research work entitled “La limite Permien-Trias en milieu continental : crise de sédimentation et/ou crise d’extinction biologique en masse ? Paléoenvironnements de dépôts et modalités de fossilisation dans les bassins permo-triasiques du Haut Atlas Marocain”. Financial support was provided by the MNHN-PPF04 project “Biodiversité actuelle et fossile. Crises, stress, restaurations et panchronisme : le message systématique”. We are deeply grateful to P. Janvier for his great interest and encouragement to our study and we thank very much the two reviewers for their useful remarks and suggestions.
The Argana Basin.
Le bassin d’Argana.
Chirotherioid traces (Argana Basin, T3 unit).
Chirotherioid traces (Argana Basin, T3 unit).
Empreintes chirothérioïdes.