An international team of paleontologists have discovered fossils of a new horse species that was about the size of a small zebra and roamed eastern Africa during the middle Pliocene, around 4.4 million years ago.

This painting shows three representatives of Hypohippus, an extinct genus of three-toed horse that lived in North America during the middle Miocene, 17 – 11 million years ago. Painting by Heinrich Harder, 1916.

“The horse fills a gap in the evolutionary history of horses but is also important for documenting how old a fossil locality is and in reconstructing habitats of human forebears of the time. This horse is one piece of a very complex puzzle that has many, many pieces,” said Prof Scott Simpson of Case Western Reserve University, who is a co-author of the paper published in the Journal of Vertebrate Paleontology.

The team unearthed teeth and bones of Eurygnathohippus woldegabrieli in 2001, in the Gona area of the Afar Region.

This fossil horse was among the diverse array of animals that lived in the same areas as the ancient human ancestor Ardipithecus ramidus.

“The fossil search team spreads out to survey for fossils in the now arid badlands of the Ethiopian desert. Among the many fossils we found are the two ends of the foreleg bone – the canon – brilliant white and well preserved in the red-tinted earth,” Prof Simpson said.

A year later, they returned and found part of the connecting shaft, which was split lengthwise but provided the crucial full length of the bone. The long slender bone indicates this ancient species was an adept runner, similar to modern zebras, and analyses of their teeth indicated they relied heavily on eating grasses in the grassy woodland environment.

This image shows a mandible of the newly discovered horse Eurygnathohippus woldegabrieli. Image credit: Bernor RL et al.

Eurygnathohippus woldegabrieli had longer legs than ancestral horses that lived and fed in forests about 6 million to 10 million years ago.

The change helped the more recent horses cover long distances as they grazed and flee lions, sabre-tooth cats and hunting hyenas that would run down their prey.

The other fossils the scientists found included teeth, which are taller than their ancestors’ and with crowns worn flatter – more signs the horses had adapted to a grazing life. Analyses of the isotopic composition of the enamel confirmed that Eurygnathohippus woldegabrieli subsisted on grass.

The species name of Eurygnathohippus woldegabrieli honors Dr Giday WoldeGabriel, a geologist at Los Alamos National Laboratory.

Source: sci.news