摘要：Evolution of the genus
Equus has been a matter of long debate with a multitude of hypotheses. Currently, there is no consensus on either the taxonomic content nor phylogeny of
Equus. Some hypotheses segregate
Equus species into three genera,
Plesippus,
Allohippus and
Equus. Also, the evolutionary role of European Pleistocene
Equus stenonis in the origin of the zebra-ass clade has been debated. Studies based on skull, mandible and dental morphology suggest an evolutionary relationship between North American Pliocene
E. simplicidens and European and African Pleistocene
Equus. In this contribution, we assess the validity of the genera
Plesippus, Allohippus and
Equus by cladistic analysis combined with morphological and morphometrical comparison of cranial anatomy. Our cladistic analysis, based on cranial and postcranial elements (30 taxa, 129 characters), supports the monophyly of
Equus, denies the recognition of
Plesippus and
Allohippus and supports the derivation of
Equus grevyi and members of the zebra-ass clade from European stenonine horses. We define the following evolutionary steps directly relevant to the phylogeny of extant zebras and asses:
E. simplicidens–
E. stenonis–
E. koobiforensis–
E. grevyi -zebra-ass clade. The North American Pliocene species
Equus simplicidens represents the ancestral stock of Old World Pleistocene
Equus and the zebra-ass clade. Our phylogenetic results uphold the most recent genomic outputs which indicate an age of 4.0–4.5 Ma for the origin and monophyly of
Equus.
