The Dmanisi Equus: Systematics, biogeography, and paleoecology.

The research article investigates the origin and spread of two species from the Equus genus, specifically Equus stenonis and Equus altidens, during the beginning of the Pleistocene era (about 2.58 million years ago) from North America into Eurasia and Africa. The research features morphologic and morphometric analysis of the Equus samples found in Dmanisi, interrogating the spread and adaptability of these species during the late Early and early Middle Pleistocene era.

Morphologic and Morphometric Analyses

• The scientists conducted detailed morphologic and morphometric analyses on the Equus samples discovered in Dmanisi. These samples exhibit morphologies close to modern hemiones (a type of wild ass) and zebras, meaning they have similar physical characteristics and sizes.
• Instead of being a generic Equus species, the researchers found that these samples actually belonged to two distinct species—Equus stenonis and Equus altidens.

Geographical Spread

• The findings showed the co-existence of both E. stenonis and E. altidens in the sequence, suggesting they lived together during the same time period.
• The researchers discovered evidence that E. stenonis, which closely matches the European E. stenonis populations morphologically, had an easternmost occurrence in Eurasia at Dmanisi.
• On the other hand, E. altidens, the research revealed, extended its range from West Asia into Greece, Germany, Italy, Spain, and possibly France, marking the oldest sightings of the species in Western Eurasia.

Adaptability and Change in Environment

• The scientists theorize that E. altidens was capable of adapting to arid or dry environmental conditions that emerged in Western Eurasia during the Pleistocene era.
• This adaptability might have led to a significant turnover in horse communities, with E. altidens dispersing from West Asia to Western Europe approximately 1.8 million years ago.
• With no substantial justification to distinguish multiple subspecies of E. altidens, the study does not support the distinction between E. altidens altidens, E. altidens granatensis, and E. stenonis mygdoniensis.