Obscure D.O.t.W: Pantydraco caducus

Name: Pantydraco caducus
Etymology: From an abbreviation of Pant-y-ffynnon Quarry where it was found, and from the Latin 'draco' (serpent or dragon); and the Latin 'caducus' (fallen)
Distribution: Late Triassic (Rhaetian) of South Wales
Type Specimen: Disarticulated skull, partial mandible (jaw), cervical vertebrae, partial forelimbs, and an incomplete right ischium (part of the pelvis)
Estimated size:  ~0.7 to 1 m long (juvenile)
First described by: Yates, 2003 (as
Thecodontosaurus caducus)

Images from of NHM, and Yates (2003), respectively

Interesting fact:  Confusing taxonomic history, and spelunky taphonomic history

The remains of the basal sauropodomorph P. caducus were first discovered in 1952, and first described as belonging to Thecodontosaurus by Kermack (1984). (Interesting side note: The genus Thecodontosaurus was first described from fossils found in Wales in 1834, and was the fourth dinosaur genera ever named (Riley and Stutchbury, 1836 vide Owen, 1842). It was described 6 years before the term Dinosauria was coined (in 1842), and furthermore wasn't recognised as a dinosaur (instead of a crocodile or other 'saurian') until 1870!) (Benton, 2012).

Closer examination of these fossils, specifically several articulated partial skeletons of juveniles, by Yates (2003) suggested that they could not be ascribed to Thecodontosaurus antiquus (Morris, 1843), and were described as a new species, Thecodontosaurus caducus. But upon further examination of fossils and cladistic analysis, Yates found more and more differences between T. antiquus and T. caducus, enough to suggest that T. caducus wasn't a Thecodontosaurus at all! This problem was solved by assigning the 'T'. caducus material to a new genus, Pantydraco (Galton et al., 2007).

As for the taphonomic history of the P. caducus remains: they were found in underground limestone cave fissure fill – yellow marl that filtered down via large cracks or solution tunnels in a limestone outcrop. Articulated dinosaur skeletons including juvenile sauropodomorphs such as P. caducus have been found fossilised in this marl. It has been postulated that "flash" storms and flooding during the Late Triassic killed these dinosaurs, drowning them and washing their bodies down the fissures into the limestone caves (Galton et al., 2010). The higher percentage of juvenile sauropodomorphs preserved may have been due to size sorting: larger carcasses could not fit down these fissures, and instead decayed and eroded on the land surface.

Simplified cladogram of all non-avian dinosaurs. P. caducus was a basal sauropodomorph.

References

Benton, M. J., 2012. Naming the Bristol dinosaur, Thecodontosaurus: politics and science in the 1830s. Proceedings of the Geologists’ Association. 123: 766-778

Galton, P. M., Yates, A. M., Kermack, D. M. 2007. Pantydraco n. gen. for Thecodontosaurus caducus Yates, 2003, a basal sauropodomorph dinosaur from the Upper Triassic or Lower Jurassic of South Wales, UK. Neues Jahrbuch für Geologie und Paläontologie Abhandlungen 243(1): 119-125

Galton, P. M., Kermack, D. 2010. The anatomy of Pantydraco caducus, a very basal sauropodomorph dinosaur from the Rhaetian (Upper Triassic) of South Wales, UK. Revue de Paléobiologie, Genève. 29 (2): 341-404

Kermack, D. 1984. New prosauropod material from South Wales. Linnean Society of London, Proceedings, 82: 101-117

Owen, R. 1842. Report on British fossil reptiles. Part II. Annual Report of the Association for the Advancement of Science, 1841, London, 9: 60-204

Riley, H., Stutchbury, S. 1836. A description of various remains of three distinct saurian animals discovered in the autumn of 1834, in the Magnesian Conglomerate on Durdham Down, near Bristol. Geological Society of London, Proceedings, 2: 397-399

Yates, A. M., 2003. A new species of the primitive dinosaur Thecodontosaurus (Saurischia: Sauropodomorpha) and its implications for the systematics of early dinosaurs. Journal of Systematic Palaeontology. 1(1): 1-42