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Hyracotherium
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Hyracotherium ("Hyrax-like beast") (also known as Eohippus) was a genus of dog-sized perissodactyl ungulates that lived in the Northern Hemisphere, with species ranging throughout Asia, Europe, and North America during the Early to Mid Eocene, about 60 to 45 million years ago. It was once considered to be the earliest known member of the Equidae before the type species was reclassified as a palaeothere, of a perissodactyl family related to both horses and brontotheres.
Discovery
The first fossils of this genus was found in England and described by the paleontologist Richard Owen in 1841.
Discussion
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Encyclopedia
Hyracotherium ("Hyrax-like beast") (also known as Eohippus) was a genus of dog-sized perissodactyl ungulates that lived in the Northern Hemisphere, with species ranging throughout Asia, Europe, and North America during the Early to Mid Eocene, about 60 to 45 million years ago. It was once considered to be the earliest known member of the Equidae before the type species was reclassified as a palaeothere, of a perissodactyl family related to both horses and brontotheres.
Discovery
The first fossils of this genus was found in England and described by the paleontologist Richard Owen in 1841. Suspecting that his species was a hyrax due to its teeth, but lacking parts of the skeleton, Owen called it a "Hyrax-like beast" and placed it in the new genus Hyracotherium. In 1876 in America Othniel C. Marsh found a full skeleton, which he placed in another new genus, Eohippus ("dawn horse"). When it became apparent that the two genera were likely one and the same, Eohippus for a time became a synonym of Hyracotherium, the genus with the earlier date of publication.
Description
Hyracotherium averaged 2 feet (60 cm) in length and 8 to 9 inches (20 cm) high at the shoulder. It had 4 toes on each front foot and 3 toes on each hind foot. The skull was long, having 44 low-crowned teeth. Hyracotherium is believed to have been a browsing herbivore that ate primarily leaves as well as some fruits and nuts.
Evolutionary role
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. It is now regarded as a paleothere, rather than a horse proper, but this is only true of the type species, H. leporinum. Most other species of Hyracotherium are still regarded as equids, but they have been placed in several other genera: Arenahippus, Minippus, Pliolophus, Protorohippus, Sifrhippus, Xenicohippus, and even Eohippus. At one time, Xenicohippus was regarded as an early brontothere.
Miscellaneous
In elementary level textbooks, Hyracotherium is commonly described as being "the size of a small Fox Terrier", which is actually 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"), in which he concluded that Henry Fairfield Osborn had so described it in a widely distributed pamphlet, Osborn being a keen fox hunter who made a natural association between horses and the dogs that accompany them.
See also
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