Superregnum: Eukaryota
Cladus: Unikonta
Cladus: Opisthokonta
Cladus: Holozoa
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: ParaHoxozoa
Cladus: Bilateria
Cladus: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Cladus: Olfactores
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Megaclassis: Osteichthyes
Cladus: Sarcopterygii
Cladus: Rhipidistia
Cladus: Tetrapodomorpha
Cladus: Eotetrapodiformes
Cladus: Elpistostegalia
Superclassis: Tetrapoda
Cladus: Reptiliomorpha
Cladus: Amniota
Cladus: Synapsida
Cladus: Eupelycosauria
Cladus: Metopophora
Cladus: Haptodontiformes
Cladus: Sphenacomorpha
Cladus: Sphenacodontia
Cladus: Therapsida
Cladus: Theriodontia
Cladus: Eutheriodontia
Cladus: Cynodontia
Cladus: Epicynodontia
Cladus: Eucynodontia
Cladus: Probainognathia
Cladus: Prozostrodontia
Cladus: Mammaliamorpha
Cladus: Mammaliaformes
Classis: Mammalia
Cladus: Theriimorpha
Cladus: Theriiformes
Cladus: Trechnotheria
Cladus: Cladotheria
Cladus: Prototribosphenida
Cladus: Zatheria
Cladus: Tribosphenida
Cladus: Boreosphenida
Subclassis: Theria
Cladus: Eutheria
Infraclassis: Placentalia
Magnordo: Boreoeutheria
Superordo: Laurasiatheria
Cladus: Scrotifera
Grandordo: Ferungulata
Mirordo: Euungulata
Ordo: Perissodactyla
Superfamilia: Equoidea
Familia: Equidae
Subfamilia: †Hyracotheriinae
Genus: †Hyracotherium
Species: H. aemulor – H. grangeri – H. index – H. pernix – H. sandrae – H. vasacciense
Name
Hyracotherium, Owen, 1841
Synonymy
Eohippus, Marsh, 1876
References
Fossilworks - Hyracotherium Accessed on 20 November 2015
Vernacular names
català: Hiracoteri
Ελληνικά: Ηώιππος
English: Hyracotherium
فارسی: کوهخرگوشدد
עברית: איוהיפוס
日本語: ヒラコテリウム
ქართული: ჰირაკოთერიუმი
한국어: 히라코테리움
മലയാളം: ഇയോഹിപ്പസ്
русский: Гиракотерии
中文: 始祖馬
Hyracotherium (/ˌhaɪrəkoʊˈθɪəriəm, -kə-/ HY-rək-o-THEER-ee-əm; "hyrax-like beast") is an extinct genus of very 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
Size comparison between Hyracotherium and a domestic cat.
Hyracotherium averaged 78 cm (2.5 feet) in length and weighed about 9 kg (20 pounds).[1] 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. Hyracotherium is believed to have been a browsing herbivore that ate primarily soft leaves as well as some fruits and nuts and plant shoots.[2]
Discovery
Holotype BMNH M16336
BMNH C21361, the second specimen
The first fossil identified as being of this genus, holotype specimen BMNH M16336, was found in the cliffs of Studd Hill near Herne Bay, Kent, and described by the paleontologist Richard Owen in a paper read to the Geological Society of London on 18 December 1839 as a "small mutilated cranium about the size of that of a hare". He identified it as belonging to an extinct order of Pachydermata, with teeth resembling those of the Chaeropotamus and the general form of the skull "partaking of a character intermediate between that of the hog and the hyrax, though the large size of the eye must have given to the physiognomy of the living animal a resemblance to that of the Rodentia." Referring to this resemblance to the hyrax, Owen proposed the genus name Hyracotherium for this new genus.[3] 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."[4][5]
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.[5] Many other North American equids were subsequently classified as species of Hyracotherium as well, but this synonymy has recently been questioned.[6]
Taxonomy and evolution
The type species, H. leporinum, is now regarded as a paleothere, rather than a horse proper.[6][7] 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.[6] At one time, Xenicohippus was regarded as an early brontothere. The main stream of horse evolution occurred on the North American continent.[citation needed]
See also
Equus
Evolution of the horse
Merychippus
Mesohippus
References
Radinsky (1978). "Evolution of brain size in carnivores and ungulates." American Naturalist: 815–831.
Solounias, N. and G. Semprebon (2002). "Advances in the reconstruction of ungulate ecomorphology with application to early fossil equids" (PDF). American Museum Novitates (3366): 1–49. doi:10.1206/0003-0082(2002)366<0001:AITROU>2.0.CO;2. hdl:2246/2855. ISSN 0003-0082.
Owen, Richard (1840). “Description of the fossil remains of a mammal, a bird, and a serpent, from the London clay.” Proceedings of the Geological Society of London, 3(66): 162–166
Owen, Richard (1841). “Description of the Fossil Remains of a Mammal (Hyracotherium leporinum) and of a Bird (Lithornis vulturinus) from the London Clay. Archived 2020-01-07 at the Wayback Machine” Transactions of the Geological Society of London, Series 2, 6: 203–208
Britain, Troy. "Feedback for June 2006". TalkOrigins Archive. Retrieved 4 May 2012.
A horse is a horse, unless of course… « Playing Chess with Pigeons, 25 May 2008
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.
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.
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