Hyracotherium

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iHyracotherium
Fossil range: Early Eocene

Extinct (fossil)

Scientific classification

Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Perissodactyla
Family:	Palaeotheriidae
Genus:	Hyracotherium Owen, 1841

Synonyms

Eohippus Marsh, 1876

Hyracotherium ("Hyrax-like beast") is considered to be the earliest known member of the horse family^[1]. It was dog-sized and four-toed and lived in the Northern Hemisphere (in Asia, Europe, and North America) during the Eocene, between 60 and 45 million years ago. ^[2]

The first fossils of this animal were found in England by the paleontologist Richard Owen in 1841, who suspected that it was a primate due to its teeth. He did not have a full skeleton and called it "Hyrax-like beast". In 1876, Othniel C. Marsh found the full skeleton in America, which he named 'Eohippus' ("dawn horse"). When it became clear that the two finds were the same species, and the first published name (Hyracotherium) has priority as the official name and Eohippus is considered a synonym.

Hyracotherium averaged only 2 feet (60 cm) in length and averaged 8 to 9 inches (20 cm) high at the shoulder. It had 4 hoofed toes on the front feet and 3 hoofed toes on each hind foot. The skull was long, having 44 long-crowned teeth. Hyracotherium is believed to have been a browsing herbivore that ate soft leaves and plant shoots. ^{[citation needed]} The Hyracotherium evolved in the Paleogene period.

It is believed by some scientists that the Hyracotherium was not only ancestral to the horse, but to other Perissodactyls such as rhinos and tapirs. ^[3]

In elementary level textbooks, Hyracotherium is commonly described as being "the size of a small fox terrier", which is about twice the size of the Hyracotherium. This arcane analogy was so curious that Stephen Jay Gould wrote an essay about it ("The Case of the Creeping Fox Terrier Clone").