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Pharisatichthys aquensis n. gen., n. sp. : un nouveau poisson fossile (Teleostei, Gerreidae) de l’Oligocène supérieur d’Aix-en-Provence (Bouches-du-Rhône, France)

Jean GAUDANT & Giorgio CARNEVALE

fr Geodiversitas 37 (1) - Pages 109-118

Published on 27 March 2015

Pharisatichthys aquensis n. gen., n. sp.: a new fossil fish (Teleostei, Gerreidae) from the late Oligocene of Aix-en-Provence (Bouches-du-Rhône, France)

The latest Oligocene of Aix-en-Provence (Bouches-du-Rhône, South France) has yielded articulated skeletons of a new genus and species of a percoid fish belonging to the family Gerreidae. Some of them are adult specimens, whereas numerous juveniles were also found in a separate fossiliferous level of the same outcrop. These specimens are here described as Pharisatichthys aquensis n. gen., n. sp.

The holotype (MNHN.F.AIX231) is a large fish reaching slightly less than 200 mm in body length, whereas the maximum body depth is about 1/3 of the body length.

Its head length equals approximately the body depth. Although it is not excellently preserved, it shows the orbit of moderate size, a rather sharp snout with a terminal mouth characterized by a remarkable development of the ascending process of the premaxillary. The posterior part of the skull roof bears a rather well-developed triangular supraoccipital crest which begins between the posterior part of the frontals; its height is about 25-30% of its length. Other specimens show an entire (spineless) posterior and ventral margin of the preopercle, and a rather long mandible, the length of which is about 2/3 of the head length. The ventral edge of the dentary is slightly concave, whereas the symphysial region is curved downwards. Several small conical teeth are present along the anterior part of the alveolar process of the dentary. Although the opercle is not adequately preserved in the available specimens, it is reasonable to conclude that its posterior edge was regularly rounded, without a well-developed spine.

The vertebral column consists of 24 vertebrae, of which 14 are postabdominal. The pleural ribs are moderately elongate. Their five posterior pairs articulate with the parapophyses, the length of which increases progressively backwards. Epineurals are present in the abdominal region.

The caudal fin is deeply forked and consists of 17 principal rays, 15 of which bifurcated. Seven to ten procurrent rays are present in front of its dorsal and ventral lobes. The caudal axial skeleton includes three vertebrae; the uro-terminal complex supports the parhypural plus five hypurals; three robust epurals are present in front of the uroneural. The second preural centrum bears a reduced neural arch and a long haemal spine, whereas the third preural centrum supports completely developed neural and haemal spines. The dorsal fin consists of nine spines and nine or ten rays, the second spine being the longest ; it is supported by about 15 pterygiophores. Three supraneurals are present in front of the dorsal pterygiophores. The predorsal formula is 0+0/0+2/1.The anal fin has three spines – the second being both the longest and the most robust – plus six (?) or seven articulated rays, supported by eight pterygiophores. The pectoral fins are incompletely preserved. The pelvic fins, which includes a robust spine, originate slightly behind the base of the pectorals. The body is covered with relatively large cycloid scales. A sheath of scales is visible at the base of the dorsal fin. The lateral line is gently arched above the vertebral column.

In spite of the relative incompleteness of the studied material, the Oligocene material of fossil fishes from Aix-en-Provence referred herein to Pharisatichthys aquensis n. gen., n. sp. exhibits a set of features that unquestionably supports its assignment to the family Gerreidae. Such assignment is justified by the physiognomy of the body, the skeletal configuration, as well as the meristic characters and especially by the presence of a large subtriangular lachrymal with entire margin, premaxilla with greatly elongate and slender ascending process coalesced with the articular process, caudal fin deeply forked and containing 17 (I+8/7+I) principal caudal-fin rays, and dorsal fin with nine spines and a sheath of large scales along its base. Pharisatichthys aquensis n. gen., n. sp. differs from all the gerreid genera in having a unique combination of features, incluing a pecular predorsal formula (0+0/0+2/ vs 0/0+2/2/, 0/0/0+2/ or 0/0+0/2/), five autogenous hypurals in the caudal skeleton, three anal-fin spines, preopercle with entire posterior margin, 14 caudal vertebrae, nine well-developed dorsal-fin spines, and absence of interhaemal cone, the latter representing a modification of the anterior portion of the first anal-fin pterygiophore for the insertion of the posterior portion of the swimbladder.

The fossil gerreids from Aix-en-Provence are the oldest undisputed occurrence of this family although otoliths of this family are also present in the Lower Miocene of South France and of New Zealand, whereas skeletal remains are known from the lower Miocene of the Upper Bhuban Formation, Surma Group, Mizoram, India.

Keywords :

Fishes, Teleostei, Gerreidae, Oligocene, new genus, new species

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