New crocodylian remains from the Solimões Formation (lower Eocene–Pliocene), State of Acre, Southwestern Brazilian Amazonia

Abstract

-The Solimões Formation (lower Eocene-Pliocene), southwestern Brazilian Amazonia, is one of the most abundant deposits of reptiles from the Cenozoic of Brazil. Eight species of Crocodylia have been described from this formation, including taxa of all the three main extant clades: Gavialoidea (Gryposuchus and Hesperogavialis), Alligatoroidea (Caiman, Mourasuchus and Purussaurus) and Crocodyloidea (Charactosuchus). Here, we describe crocodylian fossil remains collected in 1974 by RadamBrasil Project. Specimens were described and identified to the possible lowermost systematic level. With the exception of the osteoderms, the associated postcranial elements were not identified. It is concluded that at least in one location there may have been co-occurrence of four different morphotypes (Gavialoidea indet., Purussaurus sp., Mourasuchus sp. and taxa of the Brevirostres clade, but not pertaining to Purussaurus or Mourasuchus), suggesting that they could have been contemporaneous, with habitat and niche partitioning.Key words: Crocodylia, Gavialoidea, Alligatoroidea, Solimões Formation, RadamBrasil Project, Cenozoic.RESUMO -A Formação Solimões (Eoceno inferior-Plioceno) situa-se no sudoeste da Amazônia brasileira, sendo um dos depósitos fossilíferos com maior diversidade em répteis do Cenozoico brasileiro. Foram descritas oito espécies de Crocodylia para esta formação, pertencentes aos três principais clados viventes: Gavialoidea (Gryposuchus e Hesperogavialis), Alligatoroidea (Caiman, Mourasuchus e Purussaurus) e Crocodyloidea (Charactosuchus). Descrevemos aqui fragmentos fósseis coletados em 1974 sob os auspícios do Projeto RadamBrasil na Formação Solimões. Os espécimes foram descritos e identificados em seu nível sistemático menos inclusivo. Com exceção dos osteodermas, os elementos pós-cranianos associados não foram identificados. Conclui-se que pelo menos em uma localidade pode ter havido a co-ocorrência de quatro diferentes morfótipos (Gavialoidea indet., Purussaurus sp., Mourasuchus sp. e táxons do clado Brevirostres mas não pertencentes a Purussaurus ou a Mourasuchus), indicando que eles podem ter sido contemporâneos, com repartição de nichos e de hábitats.

A newMourasuchus(Alligatoroidea, Caimaninae) from the late Miocene of Venezuela, the phylogeny of Caimaninae and considerations on the feeding habits ofMourasuchus

“…Among these, there are the middle Miocene Honda Group of Colombia ( Langston, 1965 ; Langston & Gasparini, 1997 ), the Fitzcarrald Arch ( Salas-Gismondi et al, 2007 ) and the Pebas Formation of Peru ( Salas-Gismondi et al, 2015 ), and the late Miocene Solimões ( Riff et al, 2010 ) and Ituzaingó ( Bona, Riff & Gasparini, 2013 ) formations in Brazil and Argentina, respectively. The reasons for the presence of such remarkable diversities in the Miocene of South America, especially in the region of the present-day Amazon rainforest, have been discussed by several authors (e.g., Cozzuol, 2006 ; Latrubesse et al, 2010 ; Riff et al, 2010 ; Scheyer & Moreno-Bernal, 2010 ; Scheyer et al, 2013 ; Souza et al, 2016 ). Among these, the most frequently cited are the high temperatures and humidity of the region (for example see Head et al, 2009 , for temperature estimates of equatorial South America during the Paleogene), which are suitable to crocodylian physiology ( Brochu, 2011 ) and the heterogeneity of environments and habitats, which allowed the existence of diversity in several environmental factors but especially in that of prey items that permitted the evolution of an array of distinct feeding habits ( Latrubesse et al, 2010 ).…”

A large crocodyloid from the Oligocene of the Bugti Hills, Pakistan

“…Presumably, these different crocodylians inhabited the same streams but did not share the same microhabitats as is possibly the case today in India with gharials and muggers (Da Silva and Lenin, 2010) or as previously discussed in various Mesozoic and Cenozoic aquatic habitats where both mesorostrine and longirostrine forms have been described (e.g. Salas-Gismondi et al, 2015;Martin et al, 2016;Souza et al, 2016). Whatever the predator-prey interactions, this ecosystem is remarkable for the gigantic sizes attained by several of its organisms calling for further investigation of the underlying evolutionary mechanisms accounting for increase in body size.…”

On a cranial bony nodular protuberance on Mourasuchus pattersoni Cidade et al. 2017 (Crocodylia, Alligatoroidea) from the late Miocene of Venezuela

“…However, no known crocodylian fossil taxa preserve M. caudofemoralis and the insertion scars themselves are very difficult to detect in fossils (Brochu 1997). The fact that the specimen is from the 'Neogene of the Acre state' suggests it is likely from the Solimões Formation, a late Miocene unit with a diverse crocodyliform fossil record, especially of Caimaninae (see Riff et al 2010;Souza et al 2016). However, as this femur could not be reassessed, this pathological record is considered to be from a 'Crocodyliformes indet' specimen.…”