AUTHOR=Machado Helena , Avilla Leonardo TITLE=The Diversity of South American Equus: Did Size Really Matter? JOURNAL=Frontiers in Ecology and Evolution VOLUME=7 YEAR=2019 URL=https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2019.00235 DOI=10.3389/fevo.2019.00235 ISSN=2296-701X ABSTRACT=

The extant horse genus Equus originated in North America, probably during the late Miocene/early Pliocene, and its entrance into South America was possibly related to one of the last four stages of the Great American Biotic Interchange. Nonetheless, the genus had a broad geographic distribution throughout South America. Five species of Equus were traditionally recognized on this continent, although recently they have been synonymized into three: Equus neogeus, E. insulatus, and E. andium. However, the diagnoses of the three species are still unclear and a recent study showed that the characters previously used are not taxonomically valid, with the implication that in South America, Equus was represented by a single species, E. neogeus. This contribution is intended to update current knowledge on the diversity of South American Equus. Accordingly, a synthesis of prior knowledge as well as an update on the fossil distribution of Equus is presented here. Dental analyses were carried out, and the results revealed a clear overlap among the currently recognized species. Characters of the autopodia were also reanalyzed with greater sampling, and the results once again confirmed that a single species was present in South America. The update of fossil occurrences increased knowledge of the geographical distribution of the genus in South America. There are records throughout almost the entire continent, except for regions in the Amazonian rain forest, at latitudes south of 40°S, and at altitudes above 3,000 m. Furthermore, evaluating the new data with reference to geography revealed that E. neogeus formed a smooth cline, in which variation was gradual and continuous. It is also inferred that observed phenotypic variation is probably related to topography.