Résumé
L'Eocène inférieur tardif de Prémontré (Aisne) a fourni la plus riche des herpétofaunes (amphibiens et reptiles) du bassin de Paris. Il s'agit aussi, au niveau mondial, de la plus riche des herpétofaunes publiées de l'Eocène inférieur. Elle pourra être utilisée comme référence, au moins en Europe, pour l'Eocène inférieur. Le gisement a fourni 38 ou 39 espèces réparties en 27 familles. Plusieurs taxons nouveaux figurent parmi les amphibiens et les squamates ; ils seront décrits dans des travaux ultérieurs. La répartition stratigraphique de plusieurs taxons est significative ; elle conduit à placer Prémontré dans le niveau standard MP 10, ce qui concorde très exactement avec la datation donnée par les mammifères et elle s'accorde avec l'âge cuisien déjà suggéré. La signification stratigraphique de quelques taxons pourrait cependant être faussée par le fait que les microvertébrés des niveaux standards MP 11 à MP 15 sont encore mal connus. Globalement, il s'agit d'une faune typiquement laurasiatique, mais quelques éléments d'origine gondwanienne sont présents. Les formes aquatiques, dulçaquicoles surtout, sont fréquentes. Cette faune indique un climat chaud et humide, de type intertropical.
Abstract
The late Early Eocene beds at Prémontré (Paris Basin, France) have produced the richest and most diverse herpetofauna (= amphibians and reptiles) of the Paris Basin. It can serve as a reference fauna for the Early Eocene, a period for which the amphibians and reptiles are still poorly known at a world-wide scale. The locality has yielded 38 or 39 species which represent 27 families. The faunal list is as follows: Salamandridae (cf. Triturus, one indeterminate salamandrid), Palaeobatrachidae (one indetermi-nate form), Pelobatidae (one indetermi-nate form), ? Discoglossidae (one indeterminate form), ? Leptodactylidae (one indeterminate form), Podocnemididae (Neochelys sp.), Trionychidae (Trionyx sp., Eurycephalochelys aff. E. vittatus), Carettochelyidae (Allaeochelys sp.), Testudinidae (Palaeochelys sp., Hadrianus (s.l.) sp.), Alligatoridae (Allognathosuchus sp., Diplocynodon sp.), Crocodylidae (Asiatosuchus sp., Pristichampsus cf. P. rollinati), Iguanidae (Geiseltaliellus cf. G. louisi), Agamidae (Tinosaurus sp.), Cordylidae (Pseudolacerta sp.), Lacertidae (Plesiolacerta sp., one indeterminate lacertid), Anguidae (cf. Anguis, Ophisaurus (s.s.) sp., one indeterminate Glypto-saurine), Helodermatidae (one indeter-minate form), Varanoidea (one indeterminate form), Amphisbaenia (one indeterminate form), Aniliidae s.l. (Coniophis sp.), Boidae (Calamagras gallicus, one indeterminate boine, and one indeterminate pythonine or a member of a new subfamily), Tropidophiidae (Dunnophis matronensis, cf. Dunnophis), Palaeophiidae (Palaeophis typhaeus, ? Palaeophis toliapicus), Alethinophidia incertae sedis (one indeterminate form), Russellophiidae (Russellophis tenuis, one indeterminate form), Colubroidea incertae sedis (one indeterminate form). Several new taxa occur among the amphibians and squamates, and will be described in further articles. The present article is only a preliminary work. Several taxa are of particular interest. (1) A salamandrid is represented by vertebrae on which the neural spines are capped by an ornamented dermal plate. It is reminiscent of the living Asiatic Tylototriton and North American Taricha and Notophthalmus, but it also resembles the extinct Chelotriton and Brachy-cormus from the European Cenozoic. Its precise assignment within the Salamandridae remains unknown. (2) A few ilia are tentatively referred to leptodactylid frogs; they cannot belong to one of the other frog families identified at Prémontré. This typically Gondwanan family has been already reported from the Eocene of Europe. (3) The agamid lizard Tinosaurus from Prémontré is perhaps the latest representative of the family in the Eocene of Europe (a possible Tinosaurus is present in a French locality which appears to be Middle Eocene). Agamidae reappear in the European fossil record in the Oligocene. (4) An anguid lizard appears to be rather close to the living palaearctic Anguis, but it cannot be assigned to this genus. It is referred to as cf. Anguis. The oldest members of the "Anguis lineage" are represented in a few localities of the European Eocene. (5) A palatine bone belongs to a puzzling boid snake that cannot belong to the boine or erycine Boidae. It displays a feature characteristic of the pythonine boids but it also shows a character which was hitherto unknown in Boidae. This snake cannot be definitely rejected from the Pythoninae, but it could equally represent a new subfamily. (6) A small snake is only referred to as Alethinophidia incertae sedis. The overall morphology of its vertebrae is booid-like, but some characteristics are reminiscent of the Anilioidea. Its systematic position is not clear. (7) A colubroid snake is present. The Eocene appears to be the period of emergence of Colubroidea; various primitive colubroids are known in the Eocene of Europe, but the colubroid from Prémontré cannot be referred to one of the already known taxa. The other amphibian and reptile taxa from Prémontré are common constituents of the Eocene faunas from western Europe. The herpetofauna from the locality provides reliable stratigraphical information. More specifically, taxa which give the most precise indications show that the locality belongs to the standard level MP 10 of the mammal-based system of reference levels of the European Palaeogene. This age was already proposed on the basis of mammals; it is consistent with the age suggested by the study of chondrichthyes (late or latest Ypresian) and by geological data (latest Cuisian). The stratigraphical distribution of three taxa from Prémontré begins in level MP 10: the crocodile Pristichampsus, the snake Palaeophis typhaeus and, in Europe only, the turtle Hadrianus. More numerous are the taxa from Prémontré for which the stratigraphical distribution ends in MP 10: the turtle Eurycephalochelys, the snakes Calamagras gallicus, Russellophis tenuis, Palaeophis toliapicus (if this species is really present), and the lizard Geiseltaliellus louisi (if the identification is right); the snake Dunnophis matronensis could be added to these taxa, but it is not impossible that it reaches level MP 11. The significance of the latter taxa could, however, be biased because the microvertebrates from levels MP 11 to MP 15 are poorly known; in other words the ending of the stratigraphical distribution of some of the above-mentioned taxa in MP 10 could be the result of a gap in the fossil record. Nevertheless, the faunal association from Prémontré, if only at the generic level, clearly characterizes the late Ypresian. On the whole, the fauna displays a marked Laurasiatic pattern as demonstrated by the presence of Salamandridae, Palaeobatrachidae, Pelobatidae, Trionychidae, Allaeochelys, Testudinidae, Tinosaurus, Lacertidae, Anguidae, Helodermatidae, Russellophiidae, all the crocodiles, and the Discoglossidae if this family is actually present. But it also includes some taxa with Gondwanan affinities (Neochelys, the Cordylidae, Boinae, Tropidophiidae, and the Leptodactylidae if this family is really present) and a few forms for which the geographic origin is doubtful. Aquatic taxa are rather numerous; most of them were fresh-water dwellers, but palaeophiid snakes also lived in salt water. The crocodiles from Prémontré were amphibious, except Pristichampsus which was terrestrial. The presence of water is corroborated by various turtles (Trionychidae, Allaeochelys) which were good swimmers and which required broad stretches of water. Most of the taxa are indicative of a warm and humid climate.
Dernière mise à jour le 27.07.2015