Camelid

Camelids Temporal range: 45–0 Ma PreЄ Є O S D C P T J K Pg N Middle Eocene-Holocene
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 †Paracamelus †Camelops
Current range of camelids, all species

Camelids are members of the biological family Camelidae, the only currently living family in the suborder Tylopoda. The extant members of this group are: dromedary camel, Bactrian camels, wild or feral camels, llamas, alpacas, vicuñas, and guanacos.

Camelids are even-toed ungulates classified in the order Cetartiodactyla, along with pigs, hippopotami, whales, deer, giraffes, cattle, goats, antelope, and many others.

Characteristics

Camelid feet lack functional hooves, the toe bones being embedded in a broad cutaneous pad.

Camelids are large, strictly herbivorous animals with slender necks and long legs. They differ from ruminants in a number of ways. Their dentition show traces of vestigial central incisors in the upper jaw, and the third incisors have 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 in that the legs are attached to the body only at the top of the thigh, rather than attached by skin and muscle from the knee upwards. Because of this, camelids have to lie down by resting on their knees with their legs tucked underneath their bodies. They have three-chambered stomachs, rather than four-chambered ones; their upper lips are split in two, with each part separately mobile; and, uniquely among mammals, their red blood cells are elliptical. They also have a unique type of antibodies which lack 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.

Camelids do not have hooves, rather they have two-toed feet with toenails and soft foot pads (Tylopoda is Greek for "padded foot"). Most of the weight of the animal rests on 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.

Camelids are behaviorally similar in many ways, perhaps most notably in their walking gait during which both legs on the same side are moved simultaneously. The consequent swaying motion of camelids large enough for human beings to ride is legendary.

Dromedary camels, bactrian camels, llamas and alpacas are all induced ovulators.

The three Afro-Asian camel species have developed extensive adaptations to their lives 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.

Comparative table of the eight mammals in the family Camelidae (ordered by weight):

Camel-like mammal	Image	Natural range	Weight
Camelus
Bactrian camel		Central Asia (entirely domesticated)	300 to 1,000 kg (660 to 2,200 lb)
Dromedary or Arabian camel		South Asia and Middle East (entirely domesticated)	300 to 600 kg (660 to 1,320 lb)
Wild camel		Central Asia (entirely feral)
Lama
Llama		(domestic form of guanaco)	130 to 200 kg (290 to 440 lb)
Guanaco		South America	c. 90 kg (200 lb)
Vicugna
Huacaya Alpaca		(domestic form of vicuña)	48 to 84 kg (106 to 185 lb)
Suri Alpaca		(domestic form of vicuña)	48 to 84 kg (106 to 185 lb)
Vicuña		South American Andes	35 to 65 kg (77 to 143 lb)

Evolution

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 unusual in that their modern distribution is almost the inverse of their area of 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 two or three 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. A high arctic camel from this time period has been documented in the far northern reaches of Canada.

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, and possibly as a result of changing environmental conditions after the last ice age, or a combination of these factors. Three species groups survived: the dromedary of northern Africa and southwest 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 m at the shoulder, compared with the about 2 m of the largest modern camelids. Other extinct camelids included small, gazelle-like animals, such as Stenomylus. Finally, a number of very tall, giraffe-like camelids were adapted to feeding on leaves from high trees, including such genera as Aepycamelus, and Oxydactylus.

Recent genetic studies have shown that the wild Bactrian camel (Camelus ferus) is in fact a distinct species, with an independent evolutionary history to its domestic relative. Dromedary camels, Bactrian camels, llamas, and alpacas all have 74 chromosomes while the wild camel has 77 chromosomes.

Scientific classification

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

South American vicuña (Vicugna vicugna)

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
      • †Camelus sivalensis
    • Genus: Camelops
      • †Camelops hesternus
    • Genus: Paracamelus
      • †Paracamelus gigas

Phylogeny

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

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 has yet to be officially described.

External links

• Pictures of camelid species