New specimens of Mourasuchus (Alligatoroidea, Caimaninae) from the Miocene of Brazil and Bolivia and their taxonomic and morphological implications

Abstract

Cidade, G.M., Souza-Filho, J.P., Hsiou, A.S., Brochu, C.A., & Riff, D., 18 March 2019. New specimens of Mourasuchus (Alligatoroidea, Caimaninae) from the Miocene of Brazil and Bolivia and their taxonomic and anatomic implications. Alcheringa 43, 261–278. ISSN 0311-5518.

Mourasuchus is one of the most peculiar crocodylians of all time, showing an unusual ‘duck-faced’ rostrum with thin, gracile mandibles. It includes four species restricted to the South American Miocene. Here, we describe ten late Miocene specimens of Mourasuchus, nine from the Solimões Formation of Brazil and one from Bolivia. All specimens are assigned to M. arendsi, but this assignment may change as the diversity and relationships within Mourasuchus are better understood. We also discuss several issues pertinent to the morphology of Mourasuchus: the presence of a braincase neomorph (the laterocaudal bridge), hypotheses about sexual dimorphism, the function of the squamosal ‘horns’ the presence of possible thermoregulatory functions in the genus. Additionally, the paleogeographic distribution of Mourasuchus in the Miocene of South America is also discussed.

Giovanne M. Cidade* [[email protected]], Universidade de São Paulo Campus de Ribeirao Preto, Biologia, Avenida Bandeirantes 3900, Ribeirao Preto, 14040-900, Brazil; Jonas P. Souza-filho [[email protected]], Universidade Federal do Acre, Departamento de Ciências da Natureza, Campus Universitário, UFAC, BR 364, Km 4, Distrito industrial, CEP 69915-900, Rio Branco, Acre, Brazil; Annie Schmaltz Hsiou [[email protected]], Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Departamento de Biologia, Avenida dos Bandeirantes, 3900, Ribeirão Preto, 14040-901, Brazil; Christopher A. Brochu [[email protected]], University of Iowa, Iowa City, IA 52245, USA; Douglas Riff [[email protected]], Universidade Federal de Uberlandia, Uberlandia, 38400902, Brazil.

Key words:

• Mourasuchus
• Crocodylia
• Alligatoroidea
• Caimaninae
• Miocene
• South America
• Solimões Formation

Acknowledgements

The first author thanks the following people for access to collections: Carl Mehling and David Kazirian (AMNH), Marcelo Reguero (MLP), Rodrigo Machado (MCT-CPRM), Gina Oneda (CIAAP), Hyram Moreno (MCNC), Paulo Passos and Manoela Cardoso (MN Herpetology) and Patricia Holroyd (UCMP). We thank Benjamin Kear for corrections and suggestions that greatly improved the manuscript. We thank Kent Vliet (University of Florida) for sharing information on the squamosal eminences and behavior of extant crocodylians. We thank the colleagues Daniel Fortier, Paula Bona, Rafael Souza and Jorge Moreno-Bernal for bibliography and conversations that helped improve the manuscript. The funding agencies did not have any role in the study design, in the collection, analysis and interpretation of data and in the writing of the report. The authors thank Thiago G. Santana and Paulo Ricardo Lopes (Universidade de São Paulo) for help in editing the pictures.

Additional information

Funding

This work was supported by the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) grants to G.M.C. [2013/04516-1] and A.S.H. [2011/14080-0], by the Conselho de Desenvolvimento Científico e Tecnológico (CNPq) grant to G.M.C. [140808/2016-7], by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) grant to G.M.C. [Finance Code 001] and by the Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG) to D.R. [APQ-00581-09].