A CLADISTIC-ANALYSIS OF THE HORSES OF THE TRIBE EQUINI

The Equini tribe with seven genera forms a monophyletic group defined by one synapomorphy: protocone connected to the protoloph. Fourteen sp ecies are considered as the terminal taxa: Protohippus (two species), Calippus (two), Pliohippus (one), Hippidion (three), Dinohippus (three ), Astrohippus (one) and Equus (two). A cladistic analysis was perform ed using 20 characters from cranial morphology, upper and lower teeth, and appendicular skeletons. Polarity of characters was based on outgr oup criterion using the Hippotheriini tribe. For some characters, apom orphic states were identified using Merychippus, which was the sister group of both tribes. One parsimonious cladogram of 31 steps and a con sistency index of 0.77 was produced, from which a classification of th e tribe Equini was constructed. We recognize two subtribes: Protohippi na (Protohippus and Calippus) and Pliohippina subtrib. nov. (Pliohippu s, Hippidion, Dinohippus, Astrohippus and Equus). Pliohippus was the s ister group to the rest of the subtribe. The species of Hippidion form a monophyletic group and there is no evidence of a relationship betwe en 'Onohippidium' galushai, from North America, and the Hippidion grou p, from South America. Astrohippus stocki was the sister species of th e Equus-group, which includes 'Dinohippus' mexicanus. The analysis sho ws that characters mostly from the cranial morphology and upper teeth characterize the suprageneric taxa. High congruence between the strati graphical record and the phylogenetic hypothesis is observed.