Palaeoenvironmental implications of the giant crocodylian Mourasuchus (Alligatoridae,Caimaninae) in the Yecua Formation (late Miocene) of Bolivia

Tineo, D.E., Bona, P., Pérez, L.M., Vergani, G.D., González, G., Poiré, D.G., Gasparini, Z.N. & Legarreta, P., 1.10.2014. Palaeoenvironmental implications of the giant crocodylian Mourasuchus (Alligatoridae, Caimaninae) in the Yecua Formation (late Miocene) of Bolivia. Alcheringa 39, xxx–xxx. ISSN 0311-5518

Outcrops of the Yecua Formation (late Miocene) are exposed for approximately 230 m along the La Angostura section of the Piraí River (50 km southwest of Santa Cruz de la Sierra). These reveal massive (argillic palaeosols) and laminated (quiet-water lacustrine and marsh settings) mudstones interbedded with thin sandstones containing microfossils, molluscs and vertebrate remains. Significantly, the succession hosts a giant crocodylian, Mourasuchus (Alligatoridae, Caimaninae), which is represented by both skull and postcranial fragments found in association with freshwater turtles and fishes. Mourasuchus was distributed widely from the middle Miocene of Colombia to upper Miocene of Venezuela, Brazil and Argentina, suggesting connections between major fluvial systems and an active mechanism for dispersal of South American freshwater vertebrates during the Miocene.

David Eric Tineo [tineo.d.e@gmail.com] and Daniel Gustavo Poiré [dgpoire@yahoo.com.ar], CONICET—Centro de Investigaciones Geológicas, Universidad Nacional de La Plata. Calle 1 (644), B1900FWA, La Plata, Argentina; Paula Bona [paulabona26@gmail.com] and Zulma Gasparini [zgaspari@fcnym.unlp.edu.ar], CONICET—División Paleontología Vertebrados, Museo de La Plata. Paseo del Bosque s/n, B1900FWA, La Plata, Argentina; Leandro Martín Pérez [pilosaperez@gmail.com] CONICET—División Paleozoología Invertebrados, Museo de La Plata. Paseo del Bosque s/n, B1900FWA, La Plata, Argentina; Gustavo Dardo Vergani [gvergani@pluspetrol.net]—Pluspetrol S.A. Lima (339), C1073AAG, Ciudad Autónoma de Buenos Aires, Argentina; Gloria González Rigas [ggonzalez@pluspetrol.net]—Pluspetrol Bolivia Corporation SA, Av. Grigotá esq. Las Palmas, Santa Cruz de la Sierra, Bolivia; Pablo Legarreta [plegarreta@pluspetrol.net]—Pluspetrol S.A. Lima (339), C1073AAG, Ciudad Autónoma de Buenos Aires, Argentina.     

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

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* [giovannecidade@hotmail.com], Universidade de São Paulo Campus de Ribeirao Preto, Biologia, Avenida Bandeirantes 3900, Ribeirao Preto, 14040-900, Brazil; Jonas P. Souza-filho [jpdesouzafilho@hotmail.com], 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 [anniehsiou@ffclrp.usp.br], 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 [chris-brochu@uiowa.edu], University of Iowa, Iowa City, IA 52245, USA; Douglas Riff [driff2@gmail.com], Universidade Federal de Uberlandia, Uberlandia, 38400902, Brazil.