Global evolution of Equidae and Gomphotheriidae from South America.

The research article focuses on the evolution and dispersion patterns of two key migratory mammalian species in South America – horses and gomphotheres, that arrived from North America during the Pleistocene epoch. It studies their phylogeny, systematics, and ecology, while also exploring their extinction correlation with the arrival of humans.

Migration and Dispersion Patterns

• The researchers identified two genera in each of these species. In horses, these were Hippidion and Equus, and in gomphotheres, Cuvieronius and Stegomastodon.
• Both Hippidion and Equus horses exhibited small and large forms. These were found to have followed two distinct routes to migrate into South America. The smaller forms used the corridor via the Andean mountain range (known as the Andean corridor), while the larger forms spread through the eastern route and coastal areas.
• Similarly, Gomphotheres, namely Cuvieronius and Stegomastodon, followed two independent dispersion events to reach South America. Cuvieronius used the Andean corridor, whereas the larger Stegomastodon was found to have dispersed along the eastern route.

Ecological Indicators and Extinction

• The researchers studied the levels of δ(13) C and δ(18) O isotopes in these species, which indicate the type of vegetation they typically feed on and thus, their habitats. Both horses and gomphotheres presented values from woodlands to C4 grasslands.
• Interestingly, Hippidion horses had lower levels of δ(13) C than Equus in the late Pleistocene. Among gomphotheres, Cuvieronius was found in the Andean corridor, indicated by its deviation in the value of δ(18) O, while Stegomastodon thrived in the eastern plains.
• A significant observation of the research was the extinction of both these species around the time humans arrived in South America, suggesting a possible correlation between human encroachment and the extinction of these mammalian species.