New Horse Species that Lived 4.4 Million Years Ago Identified in Ethiopia

The 4.4 million year old fossil of a newfound horse species fills a missing piece of the evolutionary history of horses in the fossil record, according to the researchers who discovered the specimen at a site in Ethiopia.

The horse was about the same size as a small zebra, the researchers determined from the fossils, which were found in 2001 in the Gona area of the country's Afar region. Research co-author Scott Simpson, a professor of anatomy at Case Western Reserve's School of Medicine, said the fossils not only shed light on the evolutionary history of the horse, but also reveals data about the age of other fossils at the dig site.

"This horse is one piece of a very complex puzzle that has many, many pieces," Simpson said. The fossil horse was among many animals the lived in the region at the same time as Ardipithecus ramidus, the ancient ancestors of humans.

"The fossil search team spreads out to survey for fossils in the now arid badlands of the Ethiopian desert," Simpson said. "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."

It took Simpson and his colleagues several years to unearth the horse skeleton, finding pieces of it over time. Based on observations of a full-length leg bone, the researchers determined that the ancient horse was an adept runner, a conclusion drawn by the length of the leg bone, which was much longer than horses dated to be 2 million years of more older. An analysis of its teeth revealed it relied heavily on eating grasses.

"Grasses are like sandpaper," Simpson said. "They wear the teeth down and leave a characteristic signature of pits and scratches on the teeth so we can reliably reconstruct their ancient diets."

The three-toed grass eating horse is called Eurygnathohippus woldegabrieli - named for renowned Ethiopian geologist Giday WoldeGabriel, a principle scientists on the Middle Awash project in Ethiopia.

"Giday oversees the sedimentology, geochronology and volcanology and how the Middle Awash Valley in the Afar rift is changing shape," Simpson said. "And he leads by example, in terms of working hard. He's not afraid of a very long walk in the heat, carrying a 5-pound hammer to collect samples."

Simpson and his colleagues report their finding on the new ancient horse in the Journal of Vertebrate Paleontology.