Abstract
The Equus has a North American origin probably during the transition Miocene/Pliocene, and its entrance in South America is possibly related to one of the latest four events of the Great American Biotic Interchange. Nonetheless, the genus presented broad geographic distribution throughout South America. Traditionally, there were five species of Equus recognized to this continent and just recently they have been synonymized into three: Equus neogeus, E. insulatus and E. andium. However, their diagnoses are still unclear and a recent study showed that characters previously used are not taxonomically valid to distinguish such diversity, being inferred that in South America the genus was represented by a single species, E. neogeus. This contribution intends to update the knowledge of the diversity of South American Equus. In this sense, a synthesis of what is known so far as well as an update of the fossil record is presented here. Dental analyses were made and the results revealed a clear superimposition within the species. Also, autopodia characters were reanalyzed with greater sampling and the results once again corroborated that there was a single species presented in South America. The update of occurrences of the fossil record increased the knowledge of the geographical distribution of the genus in South America. There are records throughout almost all the continent, except for regions in the Amazon Forest, below latitude 40°, and altitudes above 3000m. Furthermore, its geographical distribution pattern along with the new incoming data revealed that E. neogeus fit as a smooth cline, in which the variation is gradual and continuous. It is also inferred that the phenotypic variation observed is probably related to the type of relief conformation.
Highlights
IntroductionThe genus Equus originated during the Early-Middle Pliocene in North America, probably in the Blancan North American Land Mammal Age (NALMA), but it was during the Pleistocene that the group reached its widest geographical range, with records on all continents except Antarctica and Australia (MacFadden, 1994; Eisenberg and Redford, 1999; Alberdi and Prado, 2004; Prado and Alberdi, 2017)
Most taxonomic revisions of South American Equus neglected the fact that morphological variations can reflect non-taxonomic factors, such as ontogeny, sexual dimorphism and individual/population differences, and adaptation driven by exposure to different environments
South American native Equus taxonomy conformed to this pattern
Summary
The genus Equus originated during the Early-Middle Pliocene in North America, probably in the Blancan North American Land Mammal Age (NALMA), but it was during the Pleistocene that the group reached its widest geographical range, with records on all continents except Antarctica and Australia (MacFadden, 1994; Eisenberg and Redford, 1999; Alberdi and Prado, 2004; Prado and Alberdi, 2017). The invasion of Equus into South America was possibly related to one of the dispersion events of the Great American Biotic Interchange (GABI) which occurred from the end of Pliocene to the terminal Pleistocene (Webb, 1978; MacFadden, 1994; Woodburne, 2010; Bacon et al, 2016). Machado et al (2018) suggested the possibility that South America might have had only a single species of native Equus, namely E. neogeus
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