Dinosauroid footprints of French Upper Triassic: discrimination, interpretation and comparison (4 fig., 2 tabl.)

• Autores: Georges Gand, Georges Demathieu
• Localización: Bulletin de la Société Géologique de France, ISSN 0037-9409, Vol. 176, Nº. 1, 2005, págs. 69-80
• Idioma: inglés
• Títulos paralelos:
  • Les traces dinosauroïdes du Trias supérieur français: discrimination, interprétation et comparaison
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• Resumen
  • English

    Dinosauroid tracks are common in France. They are mainly tridactyl II-IV feet tracks, sometimes with those of hands. A lot of these latter Coelurosaurichnus grancieri Courel & Demathieu, 2000 was discovered by MG near the village of Payzac (Ardèche department) in beds belonging to the "Ensemble gréso-dolomitique gris" (= EGDG) (fig. 1. 2). They are dated Carnian from palynological data [Fauconnier et al., 1996]. C. grancieri are tracks of feet and hands respectively 10 cm and 2.5 cm long (fig. 1. 3-5, 7-21; tabl. I-1, tabl. II). From the trackways characters, it was inferred that trackmakers were long legged, bipedal-quadrupedal reptiles, 1-2 m long.

    New discoveries made by MG in Payzac site showed the existence of a new ichnopopulation Grallator sp. (fig. 1. 25-33 ; tabl. I. II) They are only feet tracks whose trackmakers were also long-legged but only bipedal animals, a little larger that the preceding ones. Statistical comparisons with the use of Student and Snédecor tests, discriminant analysis between C. grancieri and Grallator sp. show that these two ichnopopulations are different (CG, GP, fig. 3). Also they are well distinguished with other Carnian ichnospecies of Coelurosaurichnus of Franconie = Grallator or Atreipus (Haubold & Klein, 2000) (Aal, fig. 3) and Hettangian G. variabilis of Causses (Gv, fig. 4).

    Coelurosaurichnus grancieri and Grallator sp. trackmakers were carnivorous reptiles and probably belonging to different taxa. Maybe they were only Dinosauromorpha or already theropod Dinosauria. Anyway, their presence in the lower-medium Carnian means a biodiversity for these bipedal reptiles which wwas also underlined by palichnological data from South Africa [Ellenberger, 1972] and osteological discoveries in Argentina [Bonaparte, 1993; Cuny, 1993].

    Other beds bearing dinosauroid footprints were found in Ucel Formation dated Norian [Razin et al., 1996] well exposed near Corbès [Ellenberger, 1965] and the town of la Grand-Combe [Gand et al., 2000]. All these traces are Grallator, therefore II-IV feet, about 20 cm long, probably made by Ceratosauria. The ichnopopulation G. andeolensis are clearly discriminative of Carnian Coelurosaurichnus grancieri/ Grallator sp. and Rhaetian Eubrontes (fig. 4). It was found with large Sauropoda and Prosauropoda footprints. Then, in France, frequent dinosauroid footprints have been found in Grès d'Olemps F. (Causse de Rodez) in which are Eubrontes giganteus, Grallator cf. minusculus and Dilophosauripus sp. The first two are probably due to Theropods and the latter to Ornithopodia.

    French palichnological data and those coming from West USA [Lockley and Hunt, 1995] suggest that the carnivorous bipedal reptiles size increases slowly but surely during Upper Triassic with a speeding up at the end of Rhaetian. But the presence of large Eubrontes, 43 cm long in Carnian beds of Australia means this is not true [Lucas, 2003]. Of course, it would be very interesting to find outside of Australia such large early Eubrontes. In France, also we have not met Brachychirotherium and Chirotherium : ichnites of Thécodonts which are still present in the Carnian-Norian of Germany and America [Haubold, 1984, 1986].

  • français

    Les gisements à traces dinosauroïdes du Trias supérieur ont été observés dans la bordure cévenole sauf l'un d'entre eux qui appartient au Causse de Rodez. Après que leur localisation et leur âge aient été précisés, les différentes ichnites recueillies par les auteurs sont décrites brièvement et étudiées statistiquement. Les résultats des analyses discriminantes valident les déterminations ichnospécifiques. Dans le Carnien inférieur ont été ainsi récoltées Coelurosaurichnus grancieri Courel & Demathieu, 2000 et Grallator sp. dont les ichnopoïètes auraient pu être des Dinosauromorpha ou/et des Dinosauria carnivores bipèdes. Déjà très différents entre eux, ils soulignent une biodiversité qui a été aussi mentionnée dès le Carnien moyen par les données ostéologiques. Au Norien, les empreintes Grallator sont dues à des Ceratosauria qui sont contemporaines de celles de Sauropodes et de Prosauropodes. A la fin du Trias, avec Eubrontes et Dilophosauripus, les traces dinosauroïdes sont majoritaires et grandes. Elles suggèrent la dominance de Théropodes et d'Ornithopodes parcourant les plaines d'inondation du Rhétien.