Pantydraco n. gen. for Thecodontosaurus caducus Yates, 2003, a basal sauropodomorph dinosaur from the Upper Triassic or Lower Jurassic of South Wales, UK
Abstract:Numerous isolated bones from a Rhaetian (Upper Triassic) fissure fill in Clifton, Bristol, England have been referred to the basal sauropodomorph Thecodontosaurus Riley & Stutchbury, 1836 (type genus of T. antiquus Riley & Stutchbury vide Owen, 1842). T. caducus Yates, 2003 (Rhaetian or Lower Jurassic fissure fill, South Wales) is based on several articulated partial skeletons of juvenile individuals. T. antiquus is based on the isolated neotype dentary that does not possess an autapomorphy or a unique combination of characters. This dentary is unusually short and deep but this character is also present in T. caducus and Saturnalia tupiniquim (Upper Triassic, Brazil). However, the characters of referred Clifton postcrania cannot be used to diagnose Thecodontosaurus because there are three humeral morphs from Clifton. No other bones from Clifton have characters diagnostic for T. caducus and the ages of the two fissure fills may be different. The gracile morph, long referred to T. antiquus, is present in the monospecific assemblage of 1000's of isolated sauropomorph bones from the Rhaetian fissure fill at Tytherington Quarry near Bristol. A comprehensive cladistic analysis of basal sauropodomorphs, in which T. antiquus (characters mostly based on Tytherington bones) and T. caducus were included as separate terminal taxa, failed to recover a monophyletic Thecodontosaurus in all of the most parsimonious trees. T. caducus Yates, 2003 is made the type species of Pantydraco n. gen., which can be diagnosed by the autapomorphic presence of pneumatic openings on cervical vertebrae 6-8. The prominent apex of the anteroposteriorly low asymmetrical deltopectoral crest is at 40% of humeral length (versus low at 25 %, and high at 40 % and at + 50 % in Clifton humeri) and the tubercle medial to the head is small (large in Clifton humeri).
Document Type: Research Article
Publication date: January 1, 2007
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