Hyracotherium ( ; "hyrax-like beast") is an extinct genus of small (about 60 cm in length) perissodactyl ungulates that was found in the London Clay formation. This small, fox-sized animal is (for some scientists) considered to be the earliest known member of Equidae before the type species, H. leporinum, was reclassified as a palaeothere, a perissodactyl family related to both horses and brontotheres. The remaining species are now thought to belong to different genera, such as Eohippus, which had previously been synonymised with Hyracotherium.
Description
thumb|left|Size comparison between Hyracotherium and a [[domestic cat.]]
Hyracotherium averaged 78 cm (2.5 feet) in length and weighed about 9 kg (20 pounds). It had a short face with eye sockets in the middle and a short diastema (the space between the front teeth and the cheek teeth). The skull was long, having 44 low-crowned teeth. Although it had low-crowned teeth, the beginnings of the characteristic horse-like ridges on the molars can be seen. In his formal description published by the Geological Society in 1841, Owen wrote "Without intending to imply that the present small extinct Pachyderm was more closely allied to the Hyrax than as being a member of the same order, and similar in size, I propose to call the new genus which it unquestionably indicates, Hyracotherium, with the specific name leporinum."
In 1876 Othniel C. Marsh published the description of a full skeleton found in New Mexico, which he placed in a new genus Eohippus. Its similarities with the fossils described by Owen were pointed out in a 1932 paper by Sir Clive Forster Cooper. The only species, E. angustidens, was moved to the genus Hyracotherium, which had priority as the name for the genus, with Eohippus becoming a junior synonym of that genus. Most other species of Hyracotherium are still regarded as equids, but they have been placed in several other genera, such as Arenahippus, Minippus, Sifrhippus, Xenicohippus, Pliolophus, Protorohippus and the resurrected Eohippus. Dental microwear indicates that it was a folivore that facultatively ate non-fibrous food such as fruits and seeds when they were available.
See also
- Equus
- Evolution of the horse
- Merychippus
- Mesohippus