The braincase and endocast of Parringtonia gracilis, a Middle Triassic suchian (Archosaur: Pseudosuchia)

ABSTRACT

The evolution of the braincase and brain of early pseudosuchians through to the earliest crocodylomorphs is poorly understood given the paucity of specimens, lack of well-preserved material, and lack of consensus on the phylogenetic relationships of the major clades of Pseudosuchia. Here, we describe three differently sized braincases diagnosable as belonging to the archosaur Parringtonia gracilis from the Middle Triassic Manda Beds of Tanzania. One of them, a nearly complete and exceptionally preserved braincase, possesses a complex set of character states typically present in early-diverging Pseudosuchia, but it also possesses nearly all of the character states previously hypothesized to represent synapomorphies exclusive to aetosaurs and crocodylomorphs. Details of the internal anatomy and a reconstructed endocast were obtained through high-resolution computed tomographic data and show a high degree of conservation of brain architecture across Pseudosuchia, in stark contrast to the extensive shifts observed within Theropoda to crown Aves. Integrating cranial and postcranial data into a phylogenetic analysis, we find Parringtonia gracilis to be closely related to a Revueltosaurus-Aetosauria clade at the base of Suchia and distantly related to crocodylomorphs. No matter which pseudosuchian clade is the most closely related to crocodylomorphs, we deduce that homoplasy in the braincase appears to be common across Pseudosuchia.

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Citation for this article: Nesbitt, S. J., M. R. Stocker, W. G. Parker, T. A. Wood, C. A. Sidor, and K. D. Angielczyk. 2018. The braincase and endocast of Parringtonia gracilis, a Middle Triassic suchian (Archosauria: Pseudosuchia); pp. 122–141 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

We thank L. Witmer for useful discussions. S.J.N., M.R.S., C.A.S., and K.D.A. were funded through the National Science Foundation (DBI-0306158, EAR-1337291, EAR-1337569). S.J.N. and M.R.S. were funded by the Department of Geosciences at Virginia Tech. Our work in Tanzania has been supported by National Geographic Society grants 7787–05 and 8962–11 (to C.A.S.) and additional field support from The Grainger Foundation (to K.D.A.). We thank C. Saanane (University of Dar es Salaam) as well as A. Tibaijuka and L. Nampunju (Antiquities Division, Ministry of Natural Resources and Tourism, Tanzania) for assistance in arranging and carrying out the field work. R.M.H. Smith, J. S. Steyer, and N. Tabor contributed to a productive 2012 field season in Tanzania. NMT RB28 was prepared by L. Herzog. The conclusions expressed here are those of the authors and do not represent the views of the United States Government.

Additional information

Funding

National Science Foundation DBI- 0306158,EAR-1337291,EAR-1337569