Horse outward similarity is an unreliable measure of relatedness. Besides the horse, there are six other species of genus "Equus" in the Equidae family. These are the ass or donkey, "Equus asinus"; the mountain zebra, "Equus zebra"; plains zebra, "Equus quagga"; Grévy's zebra, "Equus grevyi"; the kiang, "Equus kiang"; and the onager, "Equus hemionus". Horses can crossbreed with other members of their genus. The most common hybrid is the mule, a cross between a "jack" (male donkey) and a mare. A related hybrid, a hinny, is a cross between a stallion and a jenny (female donkey). Other hybrids include the zorse,
Equus lambei Equus lambei Equus lambei (common names include Yukon horse, and Yukon wild horse) is an extinct species of the genus "Equus". "Equus lambei" ranged across North America until approximately 10,000 years ago. Based on recent examinations of the mtDNA of "Equus lambei" remains, scientists have concluded that "E. lambei" was probably much like the extinct Tarpan, also known as the Eurasian wild horse, and the living Przewalski's Horse. A partial carcass of "Equus lambei" is on display at the Yukon Beringia Interpretive Centre in Whitehorse, Yukon. Evidence from "E. lambei" mtDNA has shown that "Equus lambei" is a close relative