Dinohippus mexicanus

Overview

Dinohippus mexicanus is an ancient horse encountered in the evolutionary setting in which modern horses emerged. It had a medium-sized body and feet supported by a single toe. Skulls and teeth from several Mexican localities reveal its appearance.^[2][1]

Key facts

Faces can vary even within the same species. A study comparing central Mexican specimens found that the depression in front of the eye varied among sites and specimens. Facial contours, as well as teeth, provide important clues to horse evolution.^[1]

Time and place

This horse is known from Hemphillian faunas of later Cenozoic North America. Important research regions include Jalisco, Guanajuato, and Zacatecas in present-day Mexico. At one locality in Zacatecas, an overlying volcanic ash layer dated to approximately 5.9 million years ago helped interpret the age of the fauna.^[1]

The time range describes source context, not the complete duration of this species.

Size, form and skeleton

The feet ended in a single toe with one hoof. Skulls, lower jaws, and molars preserve features for comparison with other horses. Considering facial outlines and tooth shapes together reveals differences among similar horses.^[2]

The species diagnosis gives a basal skull length of approximately 430 mm.^[3]

Habitat and reproduction

Traces of this horse occur in several central Mexican faunas. Comparing it with other animal fossils from the same time broadens the view from one animal’s appearance to a wider ecosystem’s history. Differences in facial form among localities add interest to these comparisons.^[1]

Fossil discovery

Lower jaws and teeth from Zacatecas joined studies comparing horse fossils from central Mexico. A 2019 study brought specimens from several sites together to examine the transition between Dinohippus and Equus. Fossils brought horses from once-separate places back together for comparison.^[1]

References

1. Dinohippus mexicanus (Early-Late, Late, and Latest Hemphillian) and the Transition to Genus Equus, in Central Mexico Faunas
2. Evolution of the Family Equidae, Subfamily Equinae, in North, Central and South America, Eurasia and Africa during the Plio-Pleistocene
3. MacFadden·Carranza-Castañeda — The skull of Dinohippus mexicanus and the origin of Equus
4. MacFadden (1984) — Study of Nannippus teeth and specimens
5. Comparative literature on body function in Nannippus

Research questions

Where can the boundary between Dinohippus and Equus be drawn? Researchers interpret their relationship by comparing facial depressions, the nasal region, and dental features. Considering several traits makes horse evolution richer than a change in just one shape.^[1]

Observation

When examining the face, first find the depression in front of the eye. Then move to the jaw and follow the molar row. Compare which regions are similar or different among specimens.^[1]