Camelid

Camelid Temporal range: 45–0 Ma PreЄ Є O S D C P T J K Pg N Middle Eocene-Recent
A Bactrian Camel walking in the snow
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Suborder:	Tylopoda
Family:	Camelidae Gray, 1821
Genera
Lama Vicugna Camelus
Map of the world showing distribution of camelids, prior to modern introductions to Australia and elsewhere. Solid black lines indicate possible migration routes.

Camelids are members of the biological family Camelidae, the only living family in the suborder Tylopoda. Dromedaries, Bactrian Camels, llamas, alpacas, vicuñas, and guanacos are in this group.

Camelids are even-toed ungulates: they are classified in the order Artiodactyla, along with pigs, hippopotamus, deer, giraffes, cattle, goats, antelope,and many others.

Characteristics

Camelid feet lack functional hooves, the toe bones being embedded in a broad cutaneous pad^[1]

Camelids are large animals with slender necks and long legs, and are strictly herbivorous. Camelids differ from true ruminants in a number of ways. Their dentition shows traces of vesitigial central incisors in the upper jaw, and the third incisors are developed into canine-like tusks. Camelids also have true canine teeth and tusk-like premolars which are separated from the molars by a gap. The musculature of the hind limbs differs from those of other ungulates by the fact that the legs are attached to the body at the top of the thigh only, rather than attached by skin and muscle from the knee downwards. Because of this, camelids have to lie down by resting on their knees with their legs tucked underneath the body.^[1] 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, 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 mammals. These so-called heavy-chain antibodies are being used to develop single-domain antibodies with potential pharmaceutical applications.

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.^[2] Many fossil camelids were unguligrade and probably hooved, in contrast to all living species.^[3]

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.^[4]

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.^[3][5]

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 (as part of the Great American Interchange that followed 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, but more likely as a result of changing environmental conditions after the last Ice Age. Three species groups survived: the Dromedary of northern Africa and south-west Asia; the Bactrian Camel of central 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.^[3]

Scientific classification

A dromedary camel (Camelus dromedarius) in the Australian outback, near Silverton, New South Wales

South American Vicuña (Vicugna vicugna)

• ORDER ARTIODACTYLA
  • Suborder Suina
  • Suborder Ruminantia
  • Suborder Tylopoda
    • †Family Xiphodontidae
    • †Family Protoceratidae
    • †Family Oromerycidae
    • †Family Merycoidodontidae
    • Family Camelidae
      • †Subfamily Poebrodontinae
      • †Subfamily Poebrotheriinae
      • †Subfamily Miolabinae
      • †Subfamily Stenomylinae
      • †Subfamily Floridatragulinae
      • Subfamily Camelinae
        • Tribe Lamini
          • Genus: Lama
            • Llama, Lama glama
            • Guanaco, Lama guanicoe
          • Genus: Vicugna
            • Vicuña, Vicugna vicugna
            • Alpaca, Vicugna pacos (previously categorized in genus Lama)
        • Tribe Camelini
          • 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	1.4 mya		Guanaco	South America
						Vicuña
		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.
Floridatragulus	Early Miocene	A bizarre species of camel with a long snout
Eulamaops	Pleistocene	From South America
Hemiauchenia	Miocene-Pleistocene	A North and South American lamine genus
Megacamelus	Miocene-Pleistocene	The largest species of Camelid
Megatylopus	Miocene-Early Pleistocene	Large camelid from North America
Oxydactylus	Early Miocene	The earliest member of the "giraffe camel" family
Palaeolama	Pleistocene	A North and South American lamine genus
Poebrotherium	Oligocene	This species of camel took the place of deer and antelope in the White River Badlands.
Procamelus	Miocene	Ancestor of extinct Titanolypus and modern Camelus.
Protylopus	Late Eocene	Earliest member of the camelids
Stenomylus	Early Miocene	Small, gazelle-like camel that lived in large herds on the Great Plains.
Titanotylopus	Miocene-Pleistocene	Tall, humped, true camel feet.

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

References

1. ^ ^{a b} Clutton-Brock, Juliet (1987). A Natural History of Domesticated Mammals. pp. 208. ISBN 0521346975. 
2. ^ Franklin, William (1984). Macdonald, D.. ed. The Encyclopedia of Mammals. New York: Facts on File. pp. 512–515. ISBN 0-87196-871-1. 
3. ^ ^{a b c} Savage, RJG, & Long, MR (1986). Mammal Evolution: an illustrated guide. New York: Facts on File. pp. 216–221. ISBN 0-8160-1194-X. 
4. ^ Wild Bactrian Camels Critically Endangered, Group Says National Geographic, 3 December 2002
5. ^ Palmer, D., ed (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. pp. 274–277. ISBN 1-84028-152-9. 

External links

• Pictures of camelid species