HORSE

a hoofed, herbivorous mammal of the family Equidae. It comprises a single species, Equus caballus, whose numerous varieties are called breeds. Before the advent of mechanized vehicles, the horse was widely used as a draft animal and riding on horseback was one of the chief means of transportation. Charles Edward Casolani The Editors of the Encyclopdia Britannica (species Equus caballus), a hoofed, herbivorous mammal of the family Equidae, order Perissodactyla, long associated with humans as a means of transport and as a draft animal. Selection and breeding have resulted in a variety of breeds that can be grouped as light (typified by the Arabian and Thoroughbred), heavy (Belgian, Percheron, etc.), and pony (Shetland, Iceland, etc.). The earliest traces of the ancestors of the horse have been found in rocks from the Eocene Epoch (57.8 to 36.6 million years ago); evidence suggests a small foxlike animal that walked on four toes but had a fifth in the form of a useless vestige. This animal, called dawn horse, or Hyracotherium, gave rise to the line that produced Orohippus, Epihippus, Mesohippus, Miohippus, Parahippus, Merychippus, Pliohippus, and, finally, Equus caballus. In this series the animal developed in size and shape and came to stand on one toe enveloped in a protective hoof. The horse family evolved mainly in North America, whence it spread via land bridges to the Old World and to South America. For uncertain reasons, the equids disappeared from the Americas some 8,000 to 10,000 years ago. According to many experts, the domestic horse breeds developed from three wild types of E. caballusPrzewalski's horse of central Asia, the tarpan of eastern Europe and Ukraine, and the forest horse of northern Europe. These wild horses were likely first hunted for food and certainly were not domesticated until long after dogs and cattle. Once tamed, the horse served as a draft animal and was used as transportation and in sport. A mature male horse is called a stallion, or, if used for breeding, a stud; mature females are mares. A castrated stallion is called a gelding. Young horses (foals) are also known as colts (males) and fillies (females). The height of a horse is measured in 4-inch (10-centimetre) units, or hands, from the highest point of the back (withers) to the ground. Its size and build determine its classification; draft horses (such as the Shire) are heavy-limbed and up to 20 hands high, ponies are less than 14.2 hands high, and light horses are intermediate, rarely exceeding 17 hands. Additional reading George G. Simpson, Horses (1951, reprinted 1970), a very readable and popular account of the horse family today and through 60,000,000 years of development, with a good bibliography; Margaret C. Self, The Horseman's Encyclopedia, rev. ed. (1963, reprinted 1978), an invaluable collection of information on domestic horses. Breed associations issue pamphlets on selected breeds of horses. See also A Standard Guide to Horse and Pony Breeds, general ed. Elwyn Hartley Edwards (1980), providing information on 150 breeds and types. The Horseman's International Book of Reference, ed. by Jean Froissard and Lily Powell Froissard (1980), is an authoritative source consisting of contributions of international experts; C.E.G. Hope and G.N. Jackson (eds.), The Encyclopedia of the Horse (1973), is a comprehensive reference work discussing, among other specific topics, the horse in mythology, literature, and art. See also John Baskett, The Horse in Art (1980). Special aspects are examined in David P. Willoughby, Growth and Nutrition in the Horse (1975); R.H. Smythe, The Horse: Structure and Movement, 2nd ed., rev. by Peter C. Goody (1972); George H. Waring, Horse Behavior: The Behavioral Traits and Adaptations of Domestic and Wild Horses, Including Ponies (1983); Moyra Williams, Horse Psychology, rev. ed. (1976); and Peter Willett, The Thoroughbred (1970). R.S. Summerhays, Encyclopaedia for Horsemen, 6th ed., rev. by Stella A. Walker (1975), is also a useful reference work. Alois Wilhelm Podhajsky The Editors of the Encyclopdia Britannica