Both caballine and stilt-legged lineages may each have comprised a single, wide-ranging species.
Jaco Weinstock, Eske Willerslev, Andrei Sher, Wenfei Tong, Simon Y W Ho, Dan Rubenstein,John Storer, James Burns, Larry Martin, Claudio Bravi, Alfredo Prieto, Duane Froese,Eric Scott, Lai Xulong, Alan Cooper 2005, 'Evolution, systematics, and phylogeography of pleistocene horses in the new world:a molecular perspective.', PLoS Biologyhttp://europepmc.org/articles/PMC1159165?pdf=render. Retrieved from PLOS CC BY 4.0 (https://creativecommons.org/licenses/by-sa/4.0/legalcode)