The evolution of mammal-like crocodyliforms in the Cretaceous Period of Gondwana

Abstract

Fossil crocodyliforms discovered in recent years1,2,3,4,5 have revealed a level of morphological and ecological diversity not exhibited by extant members of the group. This diversity is particularly notable among taxa of the Cretaceous Period (144–65 million years ago) recovered from former Gondwanan landmasses. Here we report the discovery of a new species of Cretaceous notosuchian crocodyliform from the Rukwa Rift Basin6 of southwestern Tanzania. This small-bodied form deviates significantly from more typical crocodyliform craniodental morphologies, having a short, broad skull, robust lower jaw, and a dentition with relatively few teeth that nonetheless show marked heterodonty. The presence of morphologically complex, complementary upper and lower molariform teeth suggests a degree of crown–crown contact during jaw adduction that is unmatched among known crocodyliforms, paralleling the level of occlusal complexity seen in mammals and their extinct relatives7,8,9,10,11,12. The presence of another small-bodied mammal-like crocodyliform in the Cretaceous of Gondwana indicates that notosuchians probably filled niches and inhabited ecomorphospace that were otherwise occupied by mammals on northern continents.

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Figure 1: Pakasuchus kapilimai.
Figure 2: Reconstruction of the dentition of Pakasuchus kapilimai derived from X-ray computed tomography scans.
Figure 3: Phylogenetic relationships of Pakasuchus kapilimai within crocodyliforms.

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Acknowledgements

We thank: D. Kamamba, F. Ndunguru (Tanzania Antiquities Unit), P. Msemwa (Tanzania Museum of House of Culture), I. Marobhe (University of Dar es Salaam), and the Tanzania Commission for Science and Technology for support; J.P. Cavigelli and V. Heisey for specimen preparation; M. Getty, E. Lund, S. Burch, V. Simons, E. Simons, J. Garcia-Massini, G. Masai, and A. Mussa for field assistance; P. Sereno, E. Gomani, and C. Chiumia for specimen access; J. Sidote for digital processing assistance. This research was supported by the US National Science Foundation (NSF EAR-0617561, EAR-0854218), the National Geographic Society (CRE), the University of the Witwatersrand, the Michigan State University Office of Research and Graduate Studies, and the Ohio University College of Osteopathic Medicine and Ohio University Office of Research and Sponsored Programs.

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Contributions

P.M.O., N.J.S., E.M.R. and M.D.G. developed the field project. P.M.O., J.J.W.S., N.J.S., T.L.H. and R.R. conducted the research. P.M.O., J.J.W.S., N.J.S., E.M.R., M.D.G. and S.E.N. wrote the manuscript. P.M.O., N.J.S., E.M.R., M.D.G., Z.A.J., and J.T. excavated the specimens.

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Correspondence to Patrick M. O’Connor.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Information and Data which also includes Supplementary Figures S1-S4 with legends, a Character List for Phylogenetic Analysis, a Data Matrix, legends for Supplementary Movies 1 and 2 and References. (PDF 687 kb)

41586_2010_BFnature09061_MOESM223_ESM.mov

Movie RRBP 08631 shows the reconstruction of the left side of a holotype skull, highlighting the upper and lower dentition and associated skull elements. (MOV 7192 kb)

Supplementary Movie I

Movie RRBP 08631 shows the reconstruction of the left side of a holotype skull, highlighting the upper and lower dentition and associated skull elements. (MOV 7192 kb)

41586_2010_BFnature09061_MOESM224_ESM.mov

Movie RRBP 05103 shows the reconstruction of a fragmentary skull preserving left maxilla, lower jaw and partially-preserved complement of postcaniniform teeth. (MOV 7343 kb)

Supplementary Movie 2

Movie RRBP 05103 shows the reconstruction of a fragmentary skull preserving left maxilla, lower jaw and partially-preserved complement of postcaniniform teeth. (MOV 7343 kb)

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O’Connor, P., Sertich, J., Stevens, N. et al. The evolution of mammal-like crocodyliforms in the Cretaceous Period of Gondwana. Nature 466, 748–751 (2010). https://doi.org/10.1038/nature09061

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