A new crocodyliform from the middle Cretaceous Galula Formation, southwestern Tanzania

ABSTRACT

A new taxon of peirosaurid crocodyliform, Rukwasuchus yajabalijekundu, gen. et sp. nov., is described on the basis of a well-preserved partial skull from the middle Cretaceous Galula Formation exposed in southwestern Tanzania. The skull is distinguished from those of other crocodyliforms by the presence of a mediolaterally narrow, elongate, and septate internal narial fenestra (choana) located anteriorly on the pterygoid; a markedly depressed posterior border of the parietal, excluding the supraoccipital from the dorsal cranial table; and a ventrally directed descending process of the postorbital with a well-developed posteroventral process. The lateral surface of the braincase is exquisitely preserved and includes a well-developed laterosphenoid bridge dividing the foramina for the three primary branches of the trigeminal nerve. In overall morphology, the holotype skull and isolated teeth compare closely with Hamadasuchus rebouli from the middle Cretaceous Kem Kem Beds of Morocco. Reevaluation of the problematic putative African peirosaurid taxa Stolokrosuchus lapparenti and Trematochampsa taqueti reveal a number of derived cranial characters shared with Peirosauridae and Araripesuchus. A close relationship between Rukwasuchus and other African members of Peirosauridae is supported by a parsimony analysis of Crocodyliformes. As the only known sub-Saharan peirosaurid from Africa, Rukwasuchus represents the only link between middle Cretaceous southern vertebrate faunas and much more abundant, taxonomically diverse, and potentially penecontemporaneous faunas from northern Africa.

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ACKNOWLEDGMENTS

We thank D. Kamamba, F. Ndunguru, J. Temba (Tanzania Antiquities Unit), P. Msemwa (Tanzania Museum and House of Culture), I. Marobhe, and N. Boniface (University of Dar es Salaam), and the Tanzania Commission for Science and Technology for logistical support. Thanks are also due to N. Stevens, E. Roberts, Z. Jinnah, and S. Ngasala for various forms of support on this project. We are immensely grateful to J. Groenke, S. Egberts, and W. Holloway for their skillful mechanical and digital preparation of the holotype and referred specimens, and to J. Sands, C. Pugh, and B. Keener (Holzer Clinic, Athens, Ohio) for assistance with computed tomography scanning. For assistance in the field, we thank S. Burch, J. P. Cavigelli, M. Getty, E. Lund, E. Simons, V. Simons, T. Hieronymus, G. Masai, and A. Mussa. Thanks also to D. Krause, P. Sereno, K. Seymour, D. Evans, I. Carvalho, A. Campos, S. Tavares, L. Ribeiro, and R. Allain for access to specimens. A. Turner, D. Krause, and N. Kley provided feedback on an earlier version of the manuscript. This research was supported by the National Science Foundation (DEB-1011302, EAR-0617561, EAR-0854218), the National Geographic Society (CRE), and Ohio University Heritage College of Osteopathic Medicine and Office of Research and Sponsored Programs.

Handling editor: Emily Rayfield