Dawn Horse (Hyracotherium sp.)

Late Early Eocene, Lost Cabin Age. Green River Formation. Lincoln County, Wyoming, USA. Hyracotheres are the founding fathers of the horse family. You won’t find the signature features of modern horses. Modern equids have one toe on each foot. Hyracotheres have four up front, three in the back. Modern horses have long faces, with six molar-like teeth in each jaw. Hyracotheres had short faces with only three molars. Horses today have long, rather straight legs. Hyracotheres had highly flexed joints. We know that Hyracotheres were horses because we have wonderful series of fossils that show how toes, leg joints, molars and body size changed in small steps, from 55 million years ago through to today’s fully modern horse species.