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Horse

From Wikipedia, the free encyclopedia

 

Evolution

 

Mesohippus, an ancestor of the modern horse

Mesohippus, an ancestor of the modern horse

Main article: Evolution of the horse

Horses and other equids are odd-toed ungulates of the order Perissodactyla, a relatively ancient group of browsing and grazing animals that first arose less than 10 million years after the dinosaurs became extinct. In the past, this order contained twelve families, but only three families—the horses and related species, tapirs and rhinoceroses—have survived till today. The earliest equids (belonging to the genus Hyracotherium) were found approximately 54 million years to the Eocene period. The Perissodactyls were the dominant group of large terrestrial browsing animals until the Miocene (about 20 million years ago), when even-toed ungulates, with stomachs better adapted to digesting grass, began to out compete them.

The horse as it is known today adapted by evolution to survive in areas of wide-open terrain with sparse vegetation, surviving in an ecosystem where other large grazing animals, especially ruminants, could not.[3]

Horse evolution was characterised by a reduction in the number of toes, from five per foot, to three per foot, to only one toe per foot (late Miocene 5.3 million years ago); essentially, the animal was standing on tiptoe. One of the first true horse species was the tiny Hyracotherium, which had 4 toes on each front foot (missing the thumb) and 3 toes on each back foot (missing toes 1 and 5). Over about five million years, this early equids evolved into the Orohippus. The 5th fingers vanished, and new grinding teeth evolved. This was significant in that it signaled a transition to improved browsing of tougher plant material, allowing grazing of not just leafy plants but also tougher plains grasses. Thus the proto-horses changed from leaf-eating forest-dwellers to grass-eating inhabitants of the Great Plains.

By the Pleistocene era, as the horse adapted to a drier, prairie environment, the 2nd and 4th toes disappeared on all feet, and horses became bigger. These side toes were shrinking in Hipparion and have vanished in modern horses. All that remains are a set of small vestigial bones on either side of the cannon (metacarpal or metatarsal) bone, known informally as splint bones, which are a frequent source of splints, a common injury in the modern horse.

Domestication and surviving wild species

Competing theories exist as to the time and place of initial domestication. The earliest evidence for the domestication of the horse comes from Central Asia and dates to approximately 4,500 BC. Archaeological finds such as the Sintashta chariot burials provided unequivocal evidence that the horse was definitely domesticated by 2000 BC.

Wild prototypes and modern species

Most "wild" horses today are actually feral horses (see feral horses, below), animals that had domesticated ancestors but were themselves born and live in the wild, often for generations. However, there are also some truly wild horses whose ancestors were never successfully domesticated.

The "Four Foundations" theory

There is a theory that there were four basic "proto" horses that developed with adaptations to their environment prior to domestication. There are competing theories, some arguing that the prototypes were separate species, others suggesting that the prototypes were physically different manifestations of the same species. Either way, the most common theories of historical wild species from which other types are thought to have developed suggests the following base prototypes:[4]

Przewalski's Horse, the last surviving wild horse species

Przewalski's Horse, the last surviving wild horse species

Species surviving into modern times

The tarpan, Equus ferus ferus, survived into the historical era, but became extinct in 1880. Its genetic line is lost, but its phenotype has been recreated by a "breeding back" process, in which living domesticated horses with primitive features were repeatedly interbred. Thanks to the efforts of the brothers Lutz Heck (director of the Berlin zoo) and Heinz Heck (director of Munich Tierpark Hellabrunn), the resulting Heck horse together with the Konik resembles the tarpan more closely than any other living horse.

Przewalski's Horse (Equus ferus przewalskii), a rare Asian species, is the only true wild horse alive today. Also known as the Mongolian Wild Horse, Mongolians know it as the taki, while the Kirghiz people call it a kirtag. Small wild breeding populations of this animal, named after the Russian explorer Przewalski, exist in Mongolia.[5] There are also small populations maintained at zoos throughout the world. After a battle against extinction, the Przewalksi's Horse is finally flourishing in the wild once again.

Other truly wild equids alive today include the zebra and the onager.

Feral horses

 

Free-roaming mustangs (Utah, 2005)

Free-roaming mustangs (Utah, 2005)

Feral animals, who had domesticated ancestors but were born and live in the wild, are distinct from wild animals, whose ancestors have never undergone domestication. Several populations of feral horses exist, including those in the western United States and Canada (often called "mustangs"), and in parts of Australia ("brumbies") and New Zealand ("Kaimanawa horses"). Isolated feral populations are often named for their geographic location: Namibia has its Namib Desert Horses; the Sorraia lives in Spain and Portugal; Sable Island Horses reside in Nova Scotia, Canada; and New Forest ponies have been part of Hampshire, England for a thousand years.

Studies of feral horses have provided useful insights into the behavior of ancestral wild horses, as well as greater understanding of the instincts and behaviours that drive horses.

 

 

 

Wikipedia

 

http://en.wikipedia.org/w/index.php?title=Horse&action=history

 

http://www.gnu.org/copyleft/fdl.html