What, on the other hand, do we know about environmental changes in Alaska at the time of these extinctions?
In addition, species in transition from one adaptive peak to another, undergoing rapid evolution, are often more variable.So little work has been done with these northern hemione-like equid fossils that I shall call these hemionids for simplicity, but note that their specific relationships remain uncertain.Alaskan hemionid fossils had not previously been radiocarbon dated. In this study, 19 such fossils were dated, and the fact that none of the hemionid metacarpals dated after 31,000 radiocarbon years before present (31 kyr ) makes their extinction before the Last Glacial Maximum (LGM) seem likely.In an attempt to document better the decline and demise of two Alaskan Pleistocene equids, I selected a large number of fossils from the latest Pleistocene for radiocarbon dating.Here I show that horses underwent a rapid decline in body size before extinction, and I propose that the size decline and subsequent regional extinction at 12,500 radiocarbon years before present are best attributed to a coincident climatic/vegetational shift. In contrast, fossils of the other equid Alaskan species have unusually long gracile metapodials, making them similar to the living Equus hemionus from central Asia, and also similar to fossil New World hemione-like forms.
Although the region's large mammals were evidently adapted to handle cold/arid extremes, each species was evolutionarily fine-tuned to different optimal diets and habitats.