Thecodontosaurus

Abstract: Re-examination of the surviving specimens of Thecodontosaurus antiquus indicates that this plesiomorphic sauropodomorph can be diagnosed on the basis of elongate basipterygoid processes, a relatively short dentary, and a squared posterior process of the ilium. Although much of the original topotype material found in the 1830s in Bristol, England, has now been lost, some 245 specimens remain. These indicate a small, gracile prosauropod, up to 2.5 m in length, distinguished primarily on the absence of derived characters seen in other prosauropods. Although attempts were formerly made to subdivide the Bristol specimens into several dinosaurian, and other, taxa, most appear to pertain to the prosauropod Thecodontosaurus antiquus. The specimens do indicate a clear separation into two morphs, a gracile and a robust form, presumably evidence of sexual dimorphism. A juvenile Thecodontosaurus sp. from South Wales may belong to the same species. A cladistic analysis indicates that Prosauropoda is probably ...

Abstract: Since the discovery of the basal sauropodomorph dinosaur Thecodontosaurus in the 1830s, the associated fauna from the Triassic fissures at Durdham Down (Bristol, UK) has not been investigated, largely because the quarries are built over. Other fissure sites around the Bristol Channel show that dinosaurs represented a minor part of the fauna of the Late Triassic archipelago. Here we present data on microvertebrates from the original Durdham Down fissure rocks, which considerably expand the taxonomic diversity of the island fauna, revealing that it was dominated by the sphenodontian Diphydontosaurus , and that archosauromorphs, including sphenosuchian crocodylomorphs, coelophysoid theropods, and the basal sauropodomorph Thecodontosaurus , were diverse. Importantly, a few fish teeth provide new information about the debated age of the fissure deposit, which is identified as lower Rhaetian. Thecodontosaurus had been assigned an age range over 20–25 Myr of the Late Triassic, so this narrower age determination (209.5–204 Myr) is important for studies of early dinosaurian evolution.

Abstract: The Late Triassic fissure fills from the region of Bristol, SW England and S Wales, preserve unique assemblages of small vertebrates derived from an archipelago of palaeo-islands that document aspects of a critical transition in the history of terrestrial ecosystems. Tytherington Quarry, in south Gloucestershire, is the site of several fossiliferous fissures, all dated as Rhaetian (terminal Triassic), and source of abundant remains of the ‘Bristol dinosaur’, Thecodontosaurus antiquus . In addition, the fissure sediments have yielded previously unreported microvertebrate assemblages, including over 400 jaw remains from three genera of sphenodontians and 100 archosaur teeth assigned to 15 morphotypes. The land fauna is dominated by sphenodontians, with Diphydontosaurus by far the most common form, followed by Clevosaurus , then the sauropodomorph dinosaur Thecodontosaurus , and then the sphenodontian Planocephalosaurus . There are, in addition, rare remains of contemporaneous bony fishes, as well as fossils apparently reworked from the Carboniferous limestones, namely conodonts, holocephalian (chimaeroid) teeth, and a shark tooth. Many typical latest Triassic animals, such as temnospondyls, phytosaurs, aetosaurs, rauisuchians, plateosaurids and dicynodonts are not represented at Tytherington, perhaps because these generally larger animals did not live on the palaeo-island, or because their carcasses could not fit into the fissures. The absence of tritylodonts and early mammals is, however, less easy to explain on the basis of size, although it is known that these forms were abundant here by the Early Jurassic.