Equus stenonis
Equus stenonis is an extinct species of equine that lived in Western Eurasia including Europe during the Early Pleistocene.
Taxonomy and evolution
The species was first named in 1867, with the type specimen being IGF 560, a skull with a now lost associated mandible collected from Terranuova Bracciolini in Italy. Several subspecies have been named, including E. stenonis vireti, E. stenonis guthi, E. stenonis pueblensis, E. stenonis olivolanus and E. stenonis stenonis, which likely represent different ecomorphotypes adapted to varying local conditions.Equus stenonis and other Early Pleistocene Old World Equus species are suggested to be closely related and perhaps descended from the North American species Equus simplicidens. The ancestor of Equus stenonis as well as other Early Pleistocene Old World Equus species are thought to have arrived from North America across the Bering Land Bridge as part of the Equus Datum event at the beginning of the Pleistocene, approximately 2.6 million years ago. Equus stenonis is typically considered to be closely related to other Early Pleistocene Eurasian Equus species which are collectively referred to as "stenonines" or "stenonoids". The African species Equus koobiforensis and E. oldowayensis are closely related to E. stenonis. The "stenonines" are generally thought to be the ancestral stock from which both modern zebras and asses emerged. E. stenonis has been proposed to be possibly the direct ancestor of both zebras and asses.
Barron-Ortiz et al. resurrect the genus Allohippus for Equus stenonis based on the results of their cladistic analysis regarding the interrelationships of the genus Equus, though this was subsequently rejected by other authors.