Paleodietary reconstruction of Equus simplicidens from the Hagerman Horse Quarry (Idaho, USA) highlights high abrasive habits in North American fossil equids during the Pliocene

Abstract

The evolutionary history of equids represents a paradigmatic case of evolution through time and space when, during the Cenozoic, fossil equids experimented with a variety of forms as well as multiple dietary adaptations. Nowadays, only a single genus of Equidae (Subfamily Equinae, tribe Equini) has survived, Equus, represented by wild zebras and asses and domesticated horses. In this contribution, we undertake a comprehensive mesowear analysis on the Equus simplicidens population from the Hagerman Horse Quarry, Idaho, Pliocene. Our sample includes sixty-two individuals based on crania and maxillae. We used the classic mesowear method in scoring the first or second molar paracone and calculated the average percentages of high versus low relief and sharp versus round versus blunt cusps, but also scored mesowear along a continuum that ranged from sharp cusps with high relief to blunt cusps with low relief by comparing E. simplicidens and extant ungulates. We applied the same methodology to a sample of living zebras, asses and horses to increase our comparative sample. Our results show that the Hagerman E. simplicidens sample had a high-abrasive diet as recorded in the living equid sample, and exhibited no significant distinction between the different age classes sampled. For the first time, these results show that the paleodietary behavior of E. simplicidens was similar to those of the living Equus species.