The anatomy of Teleocrater Rhadinus, an early avemetatarsalian from the lower portion of the Lifua Member of the Manda Beds (Middle Triassic)

ABSTRACT

Bird-line archosaurs (= Avemetatarsalia, the clade containing birds, dinosaurs, pterosaurs, and their kin) originated in the Triassic Period. However, the earliest evolution of this group is poorly documented because fossils are extremely rare and consist mostly of postcrania. Here, we document the osteology of Teleocrater rhadinus, an early avemetatarsalian from the lower portion of the Middle Triassic Lifua Member of the Manda Beds of the Ruhuhu Basin, southwestern Tanzania. Material of Teleocrater rhadinus includes the holotype partial skeleton comprising a single individual, including cervical, trunk, and caudal vertebrae, pectoral, pelvic, forelimb, and hind limb material, and referred specimens representing parts (skull elements, vertebrae, pectoral, pelvic, and limb elements) of at least three other individuals collected from a bonebed. Character states of the skull elements, vertebrae, girdles, and limbs indicate that Teleocrater rhadinus represents the first documented non-ornithodiran avemetatarsalian known from well-preserved, associated material. Furthermore, Teleocrater rhadinus forms part of a newly recognized clade, Aphanosauria, which also contains formerly enigmatic archosaur taxa from across Pangea, including Dongusuchus efremovi from the Middle Triassic of Russia, Yarasuchus deccanensis from the Middle Triassic of India, and Spondylosoma absconditum from the ?Middle Triassic of Brazil. This new clade and other new discoveries from the Middle to Late Triassic elucidate the sequence of character acquisitions at the base of Avemetatarsalia and fill a crucial gap in the understanding of the anatomical transformations that enabled dinosaurs to flourish later in the Mesozoic.

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Citation for this article: Nesbitt, S. J., R. J. Butler, M. D. Ezcurra, A. J. Charig, and P. M. Barrett. 2018. The anatomy of Teleocrater rhadinus, an early avemetatarsalian from the lower portion of the Lifua Member of the Manda Beds (Middle Triassic); pp. 142–177 in C. A. Sidor and S. J. Nesbitt (eds.), Vertebrate and Climatic Evolution in the Triassic Rift Basins of Tanzania and Zambia. Society of Vertebrate Paleontology Memoir 17. Journal of Vertebrate Paleontology 37(6, Supplement).

ACKNOWLEDGMENTS

Our work has been supported by a National Geographic Society grant (9606–14 to S.J.N.), NSF EAR-1337569 (to C.A.S.), NSF EAR-1337291 (to K.D.A. and S.J.N.), a Marie Curie Career Integration Grant (PCIG14-GA-2013–630123 to R.J.B.), a National Geographic Society Young Explorers grant (9467–14 to M.D.E.), and a grant from the Special Funds of the NHMUK (to P.M.B.). We thank C. Saanane (University of Dar es Salaam) and A. Tibaijuka and L. Nampunju (Antiquities Division, Ministry of Natural Resources and Tourism, Tanzania) for assistance in arranging and carrying out field work. We are grateful to M. Langer and S. Brusatte for their careful reviews. We thank L. Steel and A. C. Milner (NHMUK) for access to the holotype and comparative specimens, M. Lowe (UMCZ) for access to other material collected at the same locality and for access to F. R. Parrington's field notes, and H. Taylor (NHMUK Image Resources) for providing the photographs of the holotype specimen. Scott Hartman provided the skeletal reconstruction in Figure 1 and M. Witton provided the full reconstruction provided in Figure 29.

Additional information

Funding

Division of Earth Sciences NSF EAR-1337291,NSF EAR-1337569; National Geographic Society 9606-14