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Equidae

 
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Equidae (sometimes known as the horse family) is the taxonomic
Taxonomy

Taxonomy is the practice and science of classification. The word comes from the Greek language ', taxis and ', nomos .Taxonomies, or taxonomic schemes, are composed of taxonomic units known as taxa , or kinds of things that are arranged frequently in a hierarchical structure....
 family
Family (biology)

In biological classification, family is a taxonomic rank. Exact details of formal nomenclature depend on the Nomenclature Codes which applies....
 of horse
Horse

The horse is a hoofed mammal, a subspecies of one of seven extant species of the family Equidae. The horse has evolution of the horse over the past 45 to 55 million years from a small multi-toed creature into the large, odd-toed ungulate animal of today....
s and related animals, including the extant horse
Horse

The horse is a hoofed mammal, a subspecies of one of seven extant species of the family Equidae. The horse has evolution of the horse over the past 45 to 55 million years from a small multi-toed creature into the large, odd-toed ungulate animal of today....
s, donkey
Donkey

The 'donkey' or 'ass', Equus africanus asinus, is a Domestication member of the Equidae or horse family, and an Odd-toed ungulates. The wild ancestor of the donkey is the Wild Ass, E....
s, and zebra
Zebra

Zebras are African equids best known for their distinctive white and black stripes. Their stripes come in different patterns unique to each individual....
s, and many other species
Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring....
 known only from fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
s. All extant species are in the genus
Genus

A genus is a low-level taxonomic rank used in the classification of living and fossil organisms. The taxonomic ranks are domain , kingdom , phylum, class , order , family , genus, and species....
 Equus
Equus (genus)

Equus is a genus of animals in the Family Equidae that includes horses, donkeys, and zebras. Within Equidae, Equus is the only Extant taxon genus....
. Equidae belongs to the order Perissodactyla, which includes the extant tapir
Tapir

Tapirs are large Herbivory mammals, roughly pig-like in shape, with short, prehensile snouts. They inhabit jungle and forest regions of South America, Central America, and Southeast Asia....
s and rhinoceros
Rhinoceros

Rhinoceros , often colloquially abbreviated rhino, is a name used to group five extant species of odd-toed ungulates in the family Rhinocerotidae....
, and still more fossils.

The term equid refers to any member of this family, including any equine.

oldest known fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
s assigned to Equidae date from the early Eocene
Eocene

The Eocene Geologic time scale is a major division of the geologic timescale and the second epoch of the Palaeogene period in the Cenozoic era....
, 54 million years ago.






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Equidae (sometimes known as the horse family) is the taxonomic
Taxonomy

Taxonomy is the practice and science of classification. The word comes from the Greek language ', taxis and ', nomos .Taxonomies, or taxonomic schemes, are composed of taxonomic units known as taxa , or kinds of things that are arranged frequently in a hierarchical structure....
 family
Family (biology)

In biological classification, family is a taxonomic rank. Exact details of formal nomenclature depend on the Nomenclature Codes which applies....
 of horse
Horse

The horse is a hoofed mammal, a subspecies of one of seven extant species of the family Equidae. The horse has evolution of the horse over the past 45 to 55 million years from a small multi-toed creature into the large, odd-toed ungulate animal of today....
s and related animals, including the extant horse
Horse

The horse is a hoofed mammal, a subspecies of one of seven extant species of the family Equidae. The horse has evolution of the horse over the past 45 to 55 million years from a small multi-toed creature into the large, odd-toed ungulate animal of today....
s, donkey
Donkey

The 'donkey' or 'ass', Equus africanus asinus, is a Domestication member of the Equidae or horse family, and an Odd-toed ungulates. The wild ancestor of the donkey is the Wild Ass, E....
s, and zebra
Zebra

Zebras are African equids best known for their distinctive white and black stripes. Their stripes come in different patterns unique to each individual....
s, and many other species
Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring....
 known only from fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
s. All extant species are in the genus
Genus

A genus is a low-level taxonomic rank used in the classification of living and fossil organisms. The taxonomic ranks are domain , kingdom , phylum, class , order , family , genus, and species....
 Equus
Equus (genus)

Equus is a genus of animals in the Family Equidae that includes horses, donkeys, and zebras. Within Equidae, Equus is the only Extant taxon genus....
. Equidae belongs to the order Perissodactyla, which includes the extant tapir
Tapir

Tapirs are large Herbivory mammals, roughly pig-like in shape, with short, prehensile snouts. They inhabit jungle and forest regions of South America, Central America, and Southeast Asia....
s and rhinoceros
Rhinoceros

Rhinoceros , often colloquially abbreviated rhino, is a name used to group five extant species of odd-toed ungulates in the family Rhinocerotidae....
, and still more fossils.

The term equid refers to any member of this family, including any equine.

Evolution

The oldest known fossil
Fossil

Fossils are the preserved remains or trace fossil of animals, plants, and other organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in fossiliferous Rock formations and sedimentary rock layers is known as the fossil record....
s assigned to Equidae date from the early Eocene
Eocene

The Eocene Geologic time scale is a major division of the geologic timescale and the second epoch of the Palaeogene period in the Cenozoic era....
, 54 million years ago. They formerly were assigned to the genus Hyracotherium
Hyracotherium

Hyracotherium 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....
 (sometimes known as Eohippus), but the type species
Type species

In taxonomy, a type species is the species that originally defined a genus . It is an individual specimen that fixes the name of a genus . Two different definitions are used interchangeably, in a general term and a botanical term....
 of that genus now is regarded to be not a member of this family (see Hyracotherium
Hyracotherium

Hyracotherium 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....
). These early Equidae were fox-sized animals with three toes on the hind feet, and four on the front feet. They were herbivorous browsers on relatively soft plants, and already adapted for running. The complexity of their brains suggest that they already were alert and intelligent animals. Later species reduced the number of toes, and developed teeth more suited for grinding up grasses and other tough plant food.

The family became relatively diverse during the Miocene
Miocene

The Miocene is a Geologic time scale of the Neogene period and extends from about 23.03 to 5.33 million years before the present. As with other older geologic periods, the rock beds that define the start and end are well identified but the exact dates of the start and end of the period are uncertain....
, with many new species appearing. By this time, equids were more truly horse-like, having developed the typical body shape of the modern animals. Many of these species bore the main weight of their bodies on their central, third, toe, with the others becoming reduced, and barely touching the ground, if at all. The sole surviving genus, Equus, had evolved by the early Pleistocene
Pleistocene

The Pleistocene is the epoch from 1.8 million to 10,000 years Before Present covering the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
, and spread rapidly though the world.

Classification