Osteological redescription of the Late Triassic sauropodomorph dinosaur Thecodontosaurus antiquus based on new material from Tytherington, southwestern England

Abstract

Thecodontosaurus antiquus is a basal sauropodomorph from the Rhaetian locality of Durdham Down in Bristol, U.K. Sauropodomorph material putatively assigned to this species was found at the nearby site of Tytherington. Here, we describe the Tytherington specimens and compare them with T. antiquus and other Late Triassic sauropodomorphs from Britain. We find that this material can be assigned to T. antiquus based on multiple shared morphological traits, and we provide a revised diagnosis of this taxon. The new anatomical information from the Tytherington specimens enriches the osteology of the species, particularly of previously unknown parts of the skeleton such as the skull. We find poor anatomical support to distinguish the contemporary Pantydraco caducus from T. antiquus, such that the former might represent a juvenile of the latter. We also discuss the questionable validity of Asylosaurus yalensis. Thecodontosaurus antiquus is one of the most basal sauropodomorphs that show craniodental traits related to herbivory, while retaining a plesiomorphic limb morphology and posture. This taxon was an important component of Rhaetian insular ecosystems of southwestern Britain.

Pendraig milnerae , a new small-sized coelophysoid theropod from the Late Triassic of Wales

“…Remains of the considerably larger herbivorous sauropodomorph Th. antiquus have been preserved at the Durdham Down and Tytherington deposits [ 20 , 27 ], but only remains of the smaller sauropodomorph Pa. caducus , which might represent an immature form of Th. antiquus [ 20 ], are known from Pant-y-ffynnon [ 28 , 29 ].…”

“…antiquus have been preserved at the Durdham Down and Tytherington deposits [ 20 , 27 ], but only remains of the smaller sauropodomorph Pa. caducus , which might represent an immature form of Th. antiquus [ 20 ], are known from Pant-y-ffynnon [ 28 , 29 ]. Therefore, it is currently unclear whether predators at Pant-y-ffynon simply did not exceed the size of P. milnerae and T. gracilis , or whether larger-bodied predators in this ecosystem have not yet been discovered or preserved, possibly because taphonomic factors are biased against preservation of large-bodied animals at Pant-y-ffynon and other fissure fill deposits.…”

“…Thecodontosaurus antiquus and Pantydraco caducus , two sauropodomorph dinosaurs, represent the best studied archosaurs from the fissure fills. Thecodontosaurus antiquus was the fourth British dinosaur to be described [ 25 , 26 ] and is represented by mostly isolated remains from Durdham Down Quarry in Bristol and Tytherington Quarry (?Rhaetian) [ 20 , 27 ]. Pantydraco caducus is known from the putatively coeval Pant-y-ffynnon Quarry and is represented by a partial articulated skeleton including most of the skull, as well as a few partial skeletons and isolated elements [ 28 , 29 ].…”

“…antiquus are minor and could be attributable to taphonomic deformation or ontogenetic variation, and Pa. caducus might represent an early ontogenetic stage of Th. antiquus [ 20 ].…”

The braincase, brain and palaeobiology of the basal sauropodomorph dinosaurThecodontosaurus antiquus

“…One of the earliest members of the Sauropodomorpha is Thecodontosaurus antiquus, the first Triassic dinosaur to be named (Riley & Stutchbury, 1836, 1840, and only the sixth dinosaur ever named in the world. The original material was described by Benton et al (2000), including a detailed account of an exquisite, complete braincase and endocast, and a more complete assemblage of Thecodontosaurus fossils has been described recently (Ballell et al, 2020). Thecodontosaurus had always been regarded as Carnian in age, although regional geological and palynological evidence now points much more convincingly to a latest Triassic (Rhaetian) age, 205-201 Ma (Whiteside et al, 2016).…”