Camelid

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The four llamas and two camels are camelids: members of the biological family Camelidae, the only living family in the suborder Tylopoda.

Camelids are even-toed ungulates: they are classified in the Artiodactyla order. Other suborders of Artiodactyla include pigs, peccaries and hippos (suborder Suina) and the extraordinarily successful and diverse suborder Ruminantia (which includes cattle, goats, antelope and many others).

Characteristics

Camelids are large animals with slender necks and long legs, and are strictly herbivorous. They differ from ruminants in several ways. They have a three-chambered rather than a four-chambered digestive tract; an upper lip that is split in two with each part separately mobile; an isolated incisor in the upper jaw; and uniquely among mammals, elliptical red blood cells. They also have a unique type of antibodies lacking the light chain, in addition to the normal antibodies found in other species. These antibodies are being used to develop 'nanobodies'.

Camelids have long legs that, because they lack tensor skin to bridge between thigh and body, look longer still. They do not have hooves, rather a two-toed foot with toenails and a soft footpad (Tylopoda is Latin for "padded foot"). The main weight of the animal is borne by these tough, leathery sole-pads. The South American camelids, adapted to steep and rocky terrain, can move the pads on their toes to maintain grip. Many fossil camelids were unguligrade and probably hooved, in contrast to all living species.

Adult camelids have a single pair of incisor teeth in their upper jaw, and also have hook-shaped canines. They have a wide diastema, and grinding, selenodont, cheek teeth. Old World camelids have a larger, and somewhat variable, number of premolars than their New World counterparts. The dental formula for the New World camelids is:

The two Afro-Asian camel species have developed extensive adaptations to their life in harsh, near-waterless environments. Wild populations of the bactrian camel are even able to drink brackish water, and some herds live in nuclear test areas.

Evolution

Camelids are unusual in that their modern distribution is almost a mirror-image of their origin. Camelids first appeared very early in the evolution of the even-toed ungulates, around 45 million years ago during the middle Eocene, in present-day North America. Among the earliest camelids was the rabbit-sized Protylopus, which still had four toes on each foot. By the late Eocene around 35 million years ago, camelids such as Poebrotherium had lost the two lateral toes, and were about the size of a modern goat.

The family diversified and prospered but remained confined to the North American continent until only about 2 or 3 million years ago, when representatives arrived in Asia, and (after the formation of the Isthmus of Panama), South America.

The original camelids of North America remained common until the quite recent geological past, but then disappeared, possibly as a result of hunting or habitat alterations by the earliest human settlers. Three species groups survived: the Dromedary of northern Africa and south-west Asia; the Bactrian Camel of eastern Asia; and the South American group, which has now diverged into a range of forms that are closely related but usually classified as four species: Llamas, Alpacas, Guanacos, and Vicuñas.

Fossil camelids show a wider variety than their modern counterparts. One North American genus, Titanotylopus, stood 3.5 metres at the shoulder, compared with the approximately two metres of the largest modern camelids. Other extinct camelids included small, gazelle-like animals, such as Stenomylus. Finally, there were a number of very tall, giraffe-like camelids, adapted to feeding on leaves from high trees, including such genera as Aepycamelus, and Oxydactylus.

Scientific classification

ORDER ARTIODACTYLA

Suborder Suina
Suborder Ruminantia
Suborder Tylopoda

†Family Xiphodontidae
†Family Protoceratidae
†Family Oromerycidae
Family Camelidae

†Subfamily Poebrodontinae
†Subfamily Poebrotheriinae
†Subfamily Miolabinae
†Subfamily Stenomylidae
†Subfamily Floridatragulinae
Subfamily Camelinae

Genus: Lama

Llama, Lama glama
Guanaco, Lama guanicoe

Genus: Vicugna

Vicuña, Vicugna vicugna
Alpaca, Vicugna pacos (previously categorized in genus Lama)

Genus: Camelus

Dromedary, Camelus dromedarius
Bactrian Camel, Camelus bactrianus
†Syrian Camel
†Camelus gigas
†Camelus hesternus
†Camelus sivalensis

Phylogenetic tree

Camelid ancestor	North America 12-25 mya	Lamini	10.4 mya	6.4 mya	1.4 mya	Llama	South America
						Guanaco
					Vicuna
				Alpaca
		Camelini	8 mya	Bactrian camel			Asia
				Dromedary			Asia, Africa

Extinct genera of camelids

Genus name	Epoch	Remarks
Aepycamelus	Miocene	Tall, s-shaped neck. True padded camel feet.
Camelops	Pliocene-Pleistocene	Large, with true camel feet. Hump status uncertain.
Oxydactylus
Poebrotherium
Procamelus	Miocene	Ancestor of extinct Titanolypus and modern Camelus.
Protylopus
Stenomylus	Miocene-Pleistocene	Miniature, possibly llama-like camelid. Lacked padded "camel foot"; had hooves instead.
Titanotylopus	Miocene-Pleistocene	Tall, humped, true camel feet.

The newly discovered giant Syrian Camel is yet to be officially described.

References

External links

Pictures of camelid species

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Last updated on Saturday March 08, 2008 at 10:42:53 PST (GMT -0800)
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