Phylogenetic history of Simosuchus clarki (Crocodyliformes: Notosuchia) from the Late Cretaceous of Madagascar

ABSTRACT

The bizarre crocodyliform Simosuchus clarki shares several derived cranial characteristics with basal notosuchian taxa. In the original phylogenetic analysis assessing placement of Simosuchus among other crocodyliforms, it was recovered as a basal notosuchian. Additional preparation of the holotype skull and postcranium, and discovery of additional specimens, provides new information on the suite of morphologies in this notosuchian. Morphological analysis of all available material of S. clarki yields 60 autapomorphies distributed across the skeleton. To provide an updated test of the phylogeny of Notosuchia and placement of Simosuchus within the clade, we added seven new characters and expanded taxon sampling to include recently described notosuchians. A phylogenetic analysis of 301 characters and 84 crocodyliforms supports the position of Simosuchus as sister to Libycosuchus, more derived than Araripesuchus and Uruguaysuchus, and basal to other ziphosuchian notosuchians. We did not recover an Anatosuchus + Simosuchus clade, nor a monophyletic Araripesuchus, but did recover a peirosaurid clade including Peirosaurus, Lomasuchus, Uberabasuchus, and Hamadasuchus (but not Stolokrosaurus). We also found weak support for inclusion of Anatosuchus, Araripesuchus, Peirosauridae, and Mahajangasuchidae within Notosuchia and therefore for the conclusion that all basal mesoeucrocodylians from Gondwana, with the exception of Stolokrosuchus, are notosuchians. The results of this analysis demonstrate that basal mesoeucrocodylian relationships are currently in a state of flux and the need for caution in naming higher-level taxa until a more stable consensus topology is achieved. Similarly, large gaps in the notosuchian record render inconclusive the biogeographic origins of Simosuchus and the clade it represents on Madagascar.

ACKNOWLEDGMENTS

We thank M. Andrade, C. Brochu, R. Irmis, N. Kley, D. Krause, D. Pol, and S. Werning for helpful discussions and assistance during this research project; J. Groenke and V. Heisey for skillful preparation and casting of the Simosuchus material; J. Neville and M. Stewart for specimen photography; L. Betti-Nash for patience and perfection on the skull illustrations; and C. Brochu, S. Jouve, and D. Pol for helpful and insightful reviews. Any errors or omissions remain our own. The phylogenetic analysis was conducted using TNT, a program made freely available thanks to a subsidy by the Willi Hennig Society. Access to comparative specimens was possible thanks to J. Maisey and M. Norell (AMNH); S. Chapman and A. Milner (BMNH); A. Resetar and W. Simpson (FMNH); X. Xu (IVPP), J. Bonaparte, F. Novas, S. Apesteguía, and A. Kramarz (MACN); B. Battail (MNHN); S. Cocca, J. Cocca, and A. Garrido (MOZ); A. Ősi (Hungarian Natural History Museum); J. Calvo and L. Salgado (MUCP); D. Krause and A. Rasoamiaramanana (UA); P. Sereno (University of Chicago); I. Carvalho (UFRJ); and W. Joyce (YPM). Financial support to A.H.T. was provided by the Research Foundation of the State University of New York. Fieldwork and specimen preparation was supported by grants from the National Geographic Society and National Science Foundation to D. Krause.