Caiman australis is an extinct species of caiman described in 1858 on the basis of a left maxilla that was collected from the Upper Miocene age Ituzaingó Formation of Entre Rios, Argentina.Bravard, A. (1858). Monografıa de los terrenos marinos terciarios del Paraná. Diario oficial del Gobierno: El Nacional Argentino.[Reprinted as Burmeister, G. 1883.].Bona, P., & Barrios, F. (2015). The Alligatoroidea of Argentina: an update of its fossil record. Publicación Electrónica de la Asociación Paleontológica Argentina, 51.
Etymology The species name “australis” comes from the Greek root austral, which means “southern” after its discovery in South America.
Discovery and taxonomy Caiman australis was first described by French engineer Auguste Bravard, who had been hired by the Museo de la Confederación, on the basis of a complete left maxilla that had been collected from Upper Miocene strata belonging to the Ituzaingó Formation along the banks of the Parana River in Entre Ríos Province, Argentina.Bona, P., Riff, D., & de Gasparini, Z. B. (2012). Late Miocene crocodylians from northeast Argentina: new approaches about the austral components of the Neogene South American crocodylian fauna. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 103(3-4), 551-570.
Bravard named it Crocodilus australis in 1858, believing that it was a species of crocodile due to its elongated maxilla. It was the first named “Mesopotamian” species and the only one known for 2 decades. Bravard gave it a very brief description, but Hermann Burmeister and Cayetano Rovereto gave more detailed descriptions in 1883Burmeister, G. (1883). Reprint of Bravard, 1858: Monografía de los terrenos marinos terciarios del Paraná. Annales del Museo Público de Buenos Aires, 3, 45-94. and 1912 respectively.Rovereto, G. (1912). Los cocodrilos fósiles en las capas de Paraná. Museo nacional de hist. nat. de Buenos Aires.
The species was placed in several genera by different authors, with Juan B. Ambrosetti placing it in Proalligator in 1887,Ambrosetti, J. B. (1887). Observaciones sobre los reptiles fósiles oligocenos de los terrenos terciarios antiguos del Paraná. Florentino Ameghino placed it in Alligator in 1898,Ameghino, F. (1898). Sinopsis geológico-paleontológica de la República Argentina. Segundo censo de la República Argentina, 1. until it was finally placed in Caiman in 2012. Some additional fossils have been suggested to be from the species, but a lack of overlap prevents definitive assignment.
Description Due to the fragmentary nature of the holotype, few diagnostic traits are known for Caiman australis. C. australis had a narrow snout, with a narrower and longer maxilla than living Caiman species. The 3rd and 4th alveoli are the largest alveoli and are similarly sized, with smaller interalvelovar spaces on the maxilla. The first, second and fifth to ninth alveoli are similar in size, and the third and fourth alveoli are the largest of the maxillary tooth row, a characteristic present in some other Caiman species. The lateral margin of maxilla is also less festooned than in other Caiman species, in dorsal and lateral view. The maxilla is also adorned with an unusual predominance of prominent and elongated grooves and bumps.
Paleoenvironment Fossils of Caiman australis have been recovered from the Ituzaingó Formation of Entre Rios, Argentina, which preserves vast tidal flats similar to those in the modern day Amazon and a warm climate.Cione, A. L., Dahdul, W. M., Lundberg, J. G., & Machado-Allison, A. (2009). Megapiranha paranensis, a new genus and species of Serrasalmidae (Characiformes, Teleostei) from the upper Miocene of Argentina. Journal of Vertebrate Paleontology, 29(2), 350-358. Large, herbivorous notoungulate mammals in the Ituzaingó Formation were widespread, including the toxodontids Xotodon and Adinotherium,Schmidt, G. I. (2013). Los ungulados nativos (Litopterna y Notoungulata: Mammalia) del “Mesopotamiense”(Mioceno Tardío) de Entre Ríos, Argentina. Publicación Electrónica de la Asociación Paleontológica Argentina, 14(1). and litopterns such as Brachytherium, Cullinia, Diadiaphorus, Neobrachytherium, Oxyodontherium, Paranauchenia, Promacrauchenia, Proterotherium and Scalabrinitherium.Schmidt, G. I. (2013). Litopterna y Notoungulata (Mammalia) de la Formación Ituzaingó (Mioceno tardío-Plioceno) de la Provincia de Entre Ríos: sistemática, bioestratigrafía y paleobiogeografía (Doctoral dissertation, Universidad Nacional de La Plata). Large, armored glyptodonts like Palaehoplophorus, Eleutherocercus, and PlohophorusScillato, G. J. (2013). Los Cingulata (Mammalia, Xenarthra) del “Conglomerado Osífero”(Mioceno tardío) de la Formación Ituzaingó de Entre Ríos, Argentina. Publicación Electrónica de la Asociación Paleontológica Argentina, 14(1). lived in the area as well as other cingulates like the pampatheres Kraglievichia and Scirrotherium. Carnivores included the phorusrhacids Devincenzia and Andalgalornis and sparassodonts,Babot, J. M., & Ortiz, P. E. (2009). Primer registro de Borhyaenoidea (Mammalia, Metatheria, Sparassodonta) en la provincia de Tucumán (Formación India Muerta, Grupo Choromoro; Mioceno tardío). Acta Geológica Lilloana, 34-48. with giant crocodilians like Gryposuchus and Mourasuchus in the freshwater.Riff, D., Romano, P. S. R., Oliveira, G. R., & Aguilera, O. A. (2010). Neogene crocodile and turtle fauna in northern South America. Amazonia. Landscapes and Species Evolution: A Look Into the Past, 259-280. Bamboos, coconut palms, and other palms were prevalent.Franco, M. J., & Brea, M. (2015). First extra-Patagonian record of Podocarpaceae fossil wood in the Upper Cenozoic (Ituzaingó Formation) of Argentina. New Zealand Journal of Botany, 53(2), 103-116.
References