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The Horse (Equus caballus)
is a large ungulate mammal, one of the seven modern species of
the genus Equus. It has long played an important role in transport;
whether ridden, or when pulling a chariot, carriage, horse-drawn
boat, stagecoach, tram, also as plough horse, as well as for food.
The most common date of domestication of the horse and its first
use as a means of transport is circa 2000 BC. Until the mid 20th
century, armies used horses extensively in warfare: soldiers still
call the groups of machines that now take the place of the horse
on the battlefield "cavalry" units, sometimes keeping
traditional names (Lord Strathcona's Horse, etc.)
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In comparison
to our understanding of the development of most animals, evolutionists
have a good grasp on the evolution of the horse from the very
early (around 55 million years ago) Hyracotherium or eohippus
to the wild equids listed below. By natural selection, the toes
of early horse ancestors reduced to the single central toe which
forms the hoof of the modern equine. (Compare animals with 'cloven'
hooves (2 toes), like cows, pigs and sheep.) Vestiges of other
toes remain as the splint bones, the callus-like "chestnuts"
on the inner sides of all four legs, and the "ergots"
hidden in the hair of the underside of the fetlock joint. In his
1983 book Hen's Teeth and Horse's Toes (ISBN 0393311031), the
evolutionary biologist Stephen Jay Gould cited rare instances
of modern horses with true extra toes as evidence that minor genetic
mutations can reintroduce ancestral features.
Images 1 Though 21 Are From The Bureau Of Land Management
Images 23 And 24 Are Form The U.S.D.A.
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