In popular science horses are considered to be the archetype for demonstrating evolution within a time-stratigraphic framework. From small species, horses evolved into the large forms we know today, symbols of power and freedom. But where and when did zebras, asses and horses originate? To answer to these questions, we have to begin with the North American record, where the first zebra-like horse Equus simplicidens appeared 4 million years ago.

The Arctic ice sheet grew rapidly and extended southward into the mid-latitudes of Eurasia 2.6 million years ago and opened a land bridge between Alaska and Siberia. This allowed a faunal exchange between North America and Eurasia which included the migration of Equus simplicidens, or a larger related species of Equus, from North America into Eurasia. At the same time temperatures became cooler and climates became drier across Eurasia.

A recent study published in the Journal of Paleontology by Omar Cirilli, Raymond Louis Bernor and Lorenzo Rook has provided new insights on the earliest Pleistocene equids from Roca – Neyra, France, with implications for the final days of Hipparion and the migration of Equus into Europe. The first European horse was a large species Equus livenzovensis found at the locality of Roca-Neyra (Central France). Equus livenzovensis occurred at other European and West Asian localities and is believed to have been ancestral to the common Pleistocene European and West Asian species Equus stenonis (Figure 1). Our studies have led us to discover that Equus stenonis, or a closely related Pleistocene species, was ancestral to extant African zebra – Asian ass clade (Fig.2).

Fig.1 – Anatomical comparison of the occlusal morphology of Equus cf. E. livenzovensis from Roca Neyra (1–3) with Equus simplicidens, Equus livenzovensis, Equus stenonis vireti, Equus stenonis from Olivola and extant Equus grevyi. Colors are referred to lower fourth premolar (Blue), lower first molar (Orange) and lower second molar (Green). Scale bar 5 cm.
Fig.2 – Artwork representing the evolutionary history of modern zebras (Equus grevyi) through the North American Equus simplicidens and the European Equus stenonis.

Roca-Neyra also preserves remains of a late occurring Hipparion which is rarely found in other European early Pleistocene localities. Diverse lineages of three-toed Hipparionine horses occupied Eurasia and Africa beginning 11.2 million years ago and included diverse species lineages until 6.7 million years ago when they underwent extensive extinction. Our study has revealed that by the earliest Pleistocene 2.6 Ma, there were only three Hipparionine lineages that persisted in all of Eurasia, Proboscidipparion, Plesiohipparion and Cremohipparion.

New insights on the Early Pleistocene equids from Roca-Neyra (France, central Europe): implications for the Hipparion LAD and the Equus FAD in Europe” by Omar Cirilli, Raymond L. Bernor, Lorenzo Rook has been published in Journal of Paleontology, published by Cambridge University Press on behalf of the Paleontological Society. The article has been made freely available for a limited time.

Read other blog posts from Journal of Paleontology here
or view all blog posts from the Paleontological Society Journals

Leave a reply

Your email address will not be published.