Evolution

The Artiodactyla (even-toed herbivores) arose in the Eocene and separated into lines leading to hippos and pigs and then tylopods and ruminants (Fig. 1). Early ruminants were small forest dwellers and began to diversify in the Oligocene. The early ruminants were small forest dwellers lacking horns. Probably in this period the stomach diversified into the ruminal compartments,[5] although fossil evidence is lacking. Fossil evidence for ruminants is limited to bones, teeth, and horns. Upper incisors are missing or reduced to aid grazing. Horns appeared as body sizes became larger. Cervid antlers are deciduous bone, whereas bovid and antilocaprid horns are bone sheathed in keratin, and likely evolved independently. The bovids arose later in the Miocene when the earth's climate became drier and grasslands appeared, allowing grazing behavior to develop.

Cattle, sheep, and goats were domesticated in neolithic times, and the process of domestication greatly altered these species. Humans selected these animals for special characteristics: docility, milk production, wool, and their ability to plow and haul. The result has been specialized

Table l Suborders of Tylopoda and Ruminantia

No. of genera

No. of species

Examples

Tylopoda

Camelidae

2

4

Alpaca, llama,

camel

Ruminantia

Tragulidae

2

4

Chevrotain,

mouse deer

Giraffidae

2

2

Giraffe, okapi

Antilocapridae

1

1

Pronghorn

Cervidae

17

38

Caribou, deer,

elk, moose

Bovidae

54

120

Antelope, bison,

buffalo, cattle, gazelle, eland, goat, sheep, yak buffalo, cattle, gazelle, eland, goat, sheep, yak

breeds, of which the genetic manipulation continues. The modern dominant breeds are on a narrow genetic base, which has spread through the developed world. Some native breeds are endangered. The largest repository of genetic diversity is in Africa. The specialized domestic types are dependent upon humans for their continued survival.[1]

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