Camelids are members of the biological family Camelidae, the only currently living family in the suborder Tylopoda. The seven extant taxon members of this group are: dromedary, , wild Bactrian camels, , , vicuñas, and . Camelids are even-toed ungulates classified in the order Artiodactyla, along with species including , , deer, cattle, and .
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 have adapted to the steep and rocky terrain by adjusting the pads on their toes to maintain grip. The surface area of Camels foot pads can increase with increasing velocity in order to reduce pressure on the feet and larger members of the camelid species will usually have larger pad area, which helps to distribute weight across the foot. Many fossil camelids were unguligrade and probably hooved, in contrast to all living species.
Camelids are behaviorally similar in many ways, including their walking gait, in which both legs on the same side are moved simultaneously. While running, camelids engage a unique "running pace gait" in which limbs on the same side move in the same pattern they walk, with both left legs moving and then both right, which ensures that the fore and hind limb will not collide while in fast motion. During this motion, all four limbs momentarily are off the ground at the same time. Consequently, camelids large enough for human beings to ride have a typical swaying motion.
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. Wild Bactrian Camels Critically Endangered, Group Says National Geographic, 3 December 2002
Comparative table of the seven extant species in the family Camelidae:
Bactrian camel ( Camelus bactrianus) | Central Asia and Inner Asia (entirely domesticated) | ||||||||
Dromedary or Arabian camel ( Camelus dromedarius) | South Asia and Middle East (entirely domesticated) | ||||||||
Wild Bactrian camel ( Camelus ferus) | China and Mongolia | 300 to 820 kg (660 to 1,800 lb) | |||||||
Lama | |||||||||
Llama ( Lama glama) | (domestic form of guanaco) | ||||||||
Guanaco ( Lama guanicoe) | South America | about | |||||||
Alpaca ( Lama pacos) | (domestic form of vicuña) | ||||||||
Vicuña ( Lama vicugna) | South American Andes |
The yellow dot is the origin of the family Camelidae and the black arrows are the historic migration routes that explain the present-day distribution.]]
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 50 to 40 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, with the two living tribes, the Camelini and Lamini, diverging in the late early Miocene, about 17 million years ago, but remained restricted to North America until about 6 million years ago, when Paracamelus crossed the Bering land bridge into Eurasia, giving rise to the modern camels, and about 3-2 million years ago, when Hemiauchenia emigrated into South America (as part of the Great American Interchange), giving rise to the modern llamas. A population of Paracamelus continued living in North America and evolved into the high arctic camel, which survived until the middle Pleistocene.
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 - , , , and vicuñas. Camelids were domesticated by early Andean peoples, and remain in use today.
Fossil camelids show a wider variety than their modern counterparts. One North American genus, Titanotylopus, stood 3.5 m at the shoulder, compared with about 2.0 m for 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.
Whether the wild Bactrian camel ( Camelus ferus) is a distinct species or a subspecies ( C. bactrianus ferus) is still debated. The divergence date is 0.7 million years ago, long before the start of domestication.
Scientific classification
Phylogeny
Extinct genera
Aepycamelus Miocene Tall, s-shaped neck, true padded camel feet Aguascalientia Earliest Miocene A small, primitive, narrow-snouted floridatraguline camel from Mexico, Texas, and Panama Camelops Pliocene-Pleistocene Large, with true camel feet and hump. Status uncertain Eulamaops Pleistocene From South America Floridatragulus Early Miocene An unusual species of camel with a long snout Hemiauchenia Miocene-Pleistocene A North and South American lamine genus Megatylopus Miocene-Early Pleistocene Large camelid from North America Megacamelus Miocene-Pleistocene The largest species of camelid Michenia Early-Middle Miocene A cameline that existed for 10 million years in 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 Stevenscamelus Late Eocene Long-snouted primitive relative of Floridatragulus Titanotylopus Miocene-Pleistocene Tall, humped, true camel feet
International Year of Camelids
External links
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