Découverte d'un dinosaure sauropode tithonien dans la région de Cognac (Charente)

Abstract

Tithonian vertebrates from Cognac (Charente, France) were mentioned by Coquand as early as 1858. Buffetaut et al. (1989) described new material including actinopterygian fishes (Lepidotes sp.), squales (Lissodus sp.) and reptiles (Chelonia indet., Goniopholis sp., Pholidosaurus sp., Homoeosaurus cf. maximiliani), to which Vignaud et al. (1994) added sarcopterygian fishes (Coelacanthidae indet.), squales (Polyacrodus cf. parvidens), chelonians (Pleurosternon sp. and Tretosternon sp.) and an undetermined theropod dinosaur. The discovery of sauropod dinosaur remains in the Champblanc quarry (Cherves-de Cognac, 5 kms north of Cognac) adds new information about Tithonian vertebrates from Western France. The Champblanc specimen is a large caudal centrum (anterior and posterior width: 21 cm; anterior height: 20.5 cm; posterior height: 20 cm). The centrum is antero-posteriorly longer ventrally (7.8 cm) than dorsally (5. 5 cm). The anterior articular surface is concave; the posterior one is flat. The ventral and lateral faces are strongly concave antero-posteriorly. There are no hemapophysial facets. Laterally, a large area corresponds to the insertion of transverse processes; dorsally, the suture area of the neural arch is well-preserved. The transverse processes and the neural arch were not fused to the centrum, which is a juvenile character. Despite its large size, the Cherves sauropod was probably not a fully-grown animal. The Cherves specimen is very similar to the anterior caudals Camarasaurus, which have short centra with a deep ventral concavity (Osborn and Mook, 1921, pl. 74). According to Osborn and Mook (1921), anterior caudal centra are slightly procoelous or amphicoelous, which agrees well with the Cherves vertebra (transition point between procoely and amphicoely). The anterior caudals of Brachiosaurus are also procoelous, but the centra are much more elongated than those of Camarasaurus (Janensch, 1950). The anterior caudals of diplodocids are also slightly procoelous and more elongated and they bear pleurocoels (Gilmore, 1936; McIntosh, 1990). Sauropod remains from the French Tithonian have already been referred to the family Camarasauridae. They include teeth of Neosodon praecursor from Northern France (Buffetaut and Martin, 1993) and vertebrae from Eastern France (Buffetaut, 1990). The new specimen from Charente confirms the existence of a large Tithonian camarasaurid in France. It may belong to Neosodon praecursor, but this species is only known from isolated teeth and no direct comparison is possible with the camarasaurid from Charente.