Horses originated in North America, the first Eocene (about 56 to 35 million years ago) horses of the genus Hyracotherium ("Eohippus") were of terrier size with four toes on the front and three on the hind. They were browsers adapted to forest-floor surroundings. Through time, horses increased in size, reduced lateral toes emphasizing the middle one, grew larger teeth with higher crowns and more complex grinding surfaces, etc. By Miocene time (about 24 to 5 million years ago) horses had branched out, many adapting to life on the spreading grasslands. Modern horses (Equus) arose in North America from a progressive Pliocene (5 to 2 million years ago) horse Pliohippus that occupied the continent during the Pleistocene (2 million to 10,000 years ago) and spread to other continents at the beginning of the Pleistocene. In the Old World Equus is represented by species designated as horses, zebras and asses. After dying out in the New World, modern horses were introduced to North America from Europe by sixteenth century settlers.
Yukon horses probably arose in Beringia 200,000 years ago. Fossils have been found as far north and east as Baillie Islands, Northwest Territories; as far west as Ikpikpuk River; near the northern coast of Alaska, and as far south as Ketza River and Scottie Creek, Yukon. Many excellent specimens derived mainly from placer mining sites, came from the vicinity of Fairbanks, Alaska and the Dawson City area, Yukon. Twelve radiocarbon dates on the species range from about 31,500 to 12,300 BP and indicate that it occupied Eastern Beringia through the cold peak of the last glaciation – sometimes considered a "bottleneck". There appear to be similarities between Equus lambei of Eastern Beringia and Equus caballus lenensis from Western Siberia, but it is worth considering whether the former species ever spread southward. Comparisons should be carried out with excellent specimens referred to the small Mexican horse (Equus conversidens) from places like the 11,000 BP St. Mary Reservoir site in southern Alberta. Further, Equus conversidens dominates the excavated fauna, and the presence of horse-protein residue on two stone points from the site indicates that horses were killed or scavenged by Clovis people.
Bluefish Caves in the northwestern Yukon have yielded the earliest in situ evidence of human occupation (about 25,000 BP) of Eastern Beringia associated with one of the largest and most diverse Late Wisconsinan faunas in the region. Equus lambei fossils from the caves have been radiocarbon dated between about 17,500 and 13,000 years ago. Research on teeth of the Yukon horses from the caves indicates that predators were mainly responsible for gathering the horse bones in Cave I, whereas Caves II and III bones seem to have accumulated through accidental or natural deaths. This research also suggests that Bluefish Basin was not a polar desert, as some have claimed, during the Late Pleistocene.
Yukon horses seem to have died out about 12,000 years ago in Eastern Beringia likely due to rapid climatic change near the close of the last glaciation, possibly exacerbated by human hunting. But it is difficult to imagine that Paleoindians alone ("human overkill" hypothesis) could have wiped out so many, widespread herds both north and south of the continental ice sheets.
C.R. Harington
August, 2002