Hyracotherium: Difference between revisions
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|synonyms = ''?Eohippus'' <small>[[Othniel C. Marsh|Marsh]], 1876</small> |
|synonyms = ''?Eohippus'' <small>[[Othniel C. Marsh|Marsh]], 1876</small> |
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'''''Hyracotherium''''' ({{pron-en|ˌhaɪrəkoʊˈθɪəriəm}}, {{respell|HYE|rak-oh|THEER|ee-um}}) ("[[Hyrax]]-like beast") (also known as '''''Eohippus''''' or '''''The Dawn Horse''''') is an [[extinction|extinct]] [[genus]] of very small (averaging about 60 cm in length) [[perissodactyl]] [[ungulate]]s that lived in the woodlands of the [[Northern Hemisphere]], with species ranging throughout [[Asia]], [[Europe]], and [[North America]] during the early Tertiary Period and the early to mid [[Eocene]] Epoch, about 60 to 45 [[million]] years ago.<ref>[[Florida Museum of Natural History]] and the [[National Science Foundation]]: Fossil Horses In Cyberspace [http://www.flmnh.ufl.edu/fhc/hyraco2.htm ''Hyracotherium'', page 2]</ref> This small, dog-sized animal is the oldest known horse and was once considered to be the earliest known member of the [[Equidae]]<ref>[[Florida Museum of Natural History]] and the [[National Science Foundation]]: Fossil Horses In Cyberspace [http://www.flmnh.ufl.edu/fhc/hyraco1.htm ''Hyracotherium'', page 1]</ref> before the type species was reclassified as a [[palaeothere]], of a perissodactyl [[family (biology)|family]] related to both [[horse]]s and [[brontothere]]s. |
'''''Hyracotherium''''' ({{pron-en|ˌhaɪrəkoʊˈθɪəriəm}}, {{respell|HYE|rak-oh|THEER|ee-um}}) ("[[Hyrax]]-like beast") (also known as '''''Eohippus''''' or '''''The Dawn Horse''''') is an [[extinction|extinct]] [[genus]] of very small (averaging about 60 cm in length) [[perissodactyl]] [[ungulate]]s that lived in the woodlands of the [[Northern Hemisphere]], with species ranging throughout [[Asia]], [[Europe]], and [[North America]] during the early Tertiary Period and the early to mid [[Eocene]] Epoch, about 60 to 45 [[million]] years ago.<ref>[[Florida Museum of Natural History]] and the [[National Science Foundation]]: Fossil Horses In Cyberspace [http://www.flmnh.ufl.edu/fhc/hyraco2.htm ''Hyracotherium'', page 2]</ref> This small, dog-sized animal is the oldest known horse and was once considered to be the earliest known member of the [[Equidae]]<ref>[[Florida Museum of Natural History]] and the [[National Science Foundation]]: Fossil Horses In Cyberspace [http://www.flmnh.ufl.edu/fhc/hyraco1.htm ''Hyracotherium'', page 1]</ref> before the type species was reclassified as a [[palaeothere]], of a perissodactyl [[family (biology)|family]] related to both [[horse]]s and [[brontothere]]s. AND U HAVE NO LIFE |
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==Discovery== |
==Discovery== |
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Revision as of 18:01, 3 September 2010
| Hyracotherium Temporal range:
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| Mounted replica of a Hyracotherium vasacciensis skeleton | |
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| Genus: | Hyracotherium Owen, 1841
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| Hyracotherium leporinum Owen, 1841
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?Eohippus Marsh, 1876 | |
Hyracotherium (Template:Pron-en, HYE-rak-oh-THEER-ee-um) ("Hyrax-like beast") (also known as Eohippus or The Dawn Horse) is an extinct genus of very small (averaging about 60 cm in length) perissodactyl ungulates that lived in the woodlands of the Northern Hemisphere, with species ranging throughout Asia, Europe, and North America during the early Tertiary Period and the early to mid Eocene Epoch, about 60 to 45 million years ago.[1] This small, dog-sized animal is the oldest known horse and was once considered to be the earliest known member of the Equidae[2] before the type species was reclassified as a palaeothere, of a perissodactyl family related to both horses and brontotheres. AND U HAVE NO LIFE
Discovery
The first fossils of this genus were 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 14 inches (20 cm) high at the shoulder and weighed about 50 pounds. It had 4 hoofed toes on each front foot and 3 hoofed toes on each hind foot. Each toe had a pad on its underside, similar to those of a dog. It had a primitive, 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 long-crowned teeth. Although it had low-crowned teeth, the beginnings of the characteristic horse-like ridges on the molars can be seen. Hyracotherium is believed to have been a grazing herbivore that ate primarily soft leaves as well as some fruits and nuts and plant shoots.[3]
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.[4] It is now regarded as a paleothere, rather than a horse proper, but this is only true of the type species, H. leporinum.[5][6] 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.[6] At one time, Xenicohippus was regarded as an early brontothere. The main stream of horse evolution occurred on the North American Continent.
Common misconception on size
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", essay #10 in his book, Bully for Brontosaurus), 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
References
- ^ Florida Museum of Natural History and the National Science Foundation: Fossil Horses In Cyberspace Hyracotherium, page 2
- ^ Florida Museum of Natural History and the National Science Foundation: Fossil Horses In Cyberspace Hyracotherium, page 1
- ^ Solounias, N. and G. Semprebon (2002). "Advances in the reconstruction of ungulate ecomorphology with application to early fossil equids". American Museum Novitates. 3366: 1–49. doi:10.1206/0003-0082(2002)366<0001:AITROU>2.0.CO;2.
- ^ Florida Museum of Natural History and the National Science Foundation: Fossil Horses in Cyberspace Hyracotherium, page 3
- ^ Hooker, J.J. (1994). "The beginning of the equoid radiation". Zoological Journal of the Linnean Society. 112 (1–2): 29–63. doi:10.1006/zjls.1994.1033.
- ^ a b Froehlich, D.J. (2002). "Quo vadis eohippus? The systematics and taxonomy of the early Eocene equids (Perissodactyla)". Zoological Journal of the Linnean Society. 134 (2): 141–256. doi:10.1046/j.1096-3642.2002.00005.x.