Camelidae

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 camels, Bactrian camels, wild Bactrian camels, llamas, alpacas, vicuñas, and guanacos. Camelids are even-toed ungulates classified in the order Cetartiodactyla, along with pigs, whales, deer, cattle, antelope, and many others.

Camelids
Temporal range: 45–0 Ma Middle Eocene-Holocene
A Bactrian camel walking in the snow
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Superfamily: Cameloidea
Family: Camelidae
Gray, 1821
Tribes
Current range of camelids, all species

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

Camelids are large, strictly herbivorous animals with slender necks and long legs. They differ from ruminants in a number of ways.[2] Their dentition show traces of vestigial central incisors in the incisive bone, 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.[1] 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.[2] 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.[3] Many fossil camelids were unguligrade and probably hooved, in contrast to all living species.[4]

Camelids are behaviorally similar in many ways, including their walking gait, in which both legs on the same side are moved simultaneously. 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.[5]

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.[6]

Comparative table of the seven extant species in the family Camelidae:

Species Image Natural range Weight
Camelus
Bactrian camel

(Camelus bactrianus)

 Central and Inner Asia
(entirely domesticated)		 300 to 1,000 kg (660 to 2,200 lb)
Wild Bactrian camel

(Camelus ferus)

 China and Mongolia
(entirely wild)		 300 to 820 kg (660 to 1,800 lb)
Dromedary
or
Arabian camel

(Camelus dromedarius)

 South Asia and Middle East
(entirely domesticated)		 300 to 600 kg (660 to 1,320 lb)
Lama
Llama

(Lama glama)

 (domestic form of guanaco) 130 to 200 kg (290 to 440 lb)
Guanaco

(Lama guanicoe)

 South America c. 90 to 120 kg (200 to 260 lb)
Vicugna
Alpaca

(Vicugna pacos)

 (domestic form of vicuña) 48 to 84 kg (106 to 185 lb)
Vicuña

(Vicugna vicugna)

 South American Andes 35 to 65 kg (77 to 143 lb)

Evolution
Camelid
Lamini
Lama
 

Glama

 
 

Guanicoe

 
 
Vicugna
 

Vicugna

 
 

Paco

 
 
 
Camelini
Camelus
 

Bactrianus

 
 

Dromedarius

 
 
†Camelops
⊞
 

Kansanus

 
 

Hesternus

 
 

Minodokae

 
⊟
 
 
 
A family tree indicating different species within the Camelidae genus[7]
A dymaxion map of the biogeographic distribution of Camelidae species:
  Tertiary distribution
  Present-day distributions
  Introduced (feral) distributions
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 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.[4][8]

The family diversified and prospered, but remained confined to the North American continent until only about two to 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. Camelids were domesticated by early Andean peoples[9] 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 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.[4]

Whether the wild Bactrian camel (Camelus ferus) is in fact a distinct species or a subspecies (Camelus bactrianus ferus) is still debated.[10][11] The divergence date is 0.7 million years ago, long before the start of domestication.[11]

Scientific classification
A dromedary camel (C. dromedarius) in the Australian outback, near Silverton, New South Wales
South American vicuña (Vicugna vicugna)

Family Camelidae

Phylogeny
Camelid ancestor
 
 
Hemiauchenia
 (10.3 to 0.012 mya[12])
 

Lama guanicoe

 
 

Lama glama

 
 Lama
 
Palaeolama
 (1.8 to 0.012 mya[13])
 
 
 

Vicugna pacos

 
 

Vicugna vicugna

 
 Vicugna
 
Blancocamelus
 (1.8 to 0.3 mya[14])
 
Pleiolama
 (10.3 to 2.588 mya[15])
 
 Lamini
 
 
Camelops
 (2.588 to 0.012 mya[16])
 
Paracamelus
 (11.608 to 0.781 mya[17][18])
 

Bactrian Camel

 
 

Dromedary

 
 Camelus
 
Procamelus
 (15.97 to 5.332 mya[19])
 
 Camelini
 
 
Hesperocamelus
 (20.43 to 15.97 mya[20])
 
 
  Endemic to South America
  Endemic to North and South America
  Endemic to North America
  Endemic to Asia
  Endemic to Asia and 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
Eulamaops Pleistocene From South America
Floridatragulus Early Miocene A bizarre species of camel with a long snout
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.

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References
  1. Clutton-Brock, Juliet (1987). A Natural History of Domesticated Mammals. p. 208. ISBN 978-0-521-34697-9.
  2. Fowler, M.E. (2010). "Medicine and Surgery of Camelids", Ames, Iowa: Wiley-Blackwell. Chapter 1 General Biology and Evolution addresses the fact that camelids (including camels and llamas) are not ruminants, pseudo-ruminants, or modified ruminants.
  3. Franklin, William (1984). Macdonald, D. (ed.). The Encyclopedia of Mammals. New York: Facts on File. pp. 512–515. ISBN 978-0-87196-871-5.
  4. Savage, RJG; Long, MR (1986). Mammal Evolution: an illustrated guide. New York: Facts on File. pp. 216–221. ISBN 978-0-8160-1194-0.
  5. Chen, B.X.; Yuen, Z.X. & Pan, G.W. (1985). "Semen-induced ovulation in the bactrian camel (Camelus bactrianus)" (PDF). J. Reprod. Fertil. 74 (2): 335–339. doi:10.1530/jrf.0.0740335. PMID 3900379. Retrieved September 12, 2014.
  6. Wild Bactrian Camels Critically Endangered, Group Says National Geographic, 3 December 2002
  7. "Animal Diversity Web." ADW: Camelidae: CLASSIFICATION. N.p., n.d. Web. 09 June 2017.
  8. Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. pp. 274–277. ISBN 978-1-84028-152-1.
  9. Moore, Katherine M. (2016). Early Domesticated Camelids in the Andes. In "The Archaeology of Andean Pastoralism", Jose M. Capriles and Nicholas Tripcevich eds.
  10. Cui, Peng; Ji, Rimutu; Ding, Feng; Qi, Dan; Gao, Hongwei; Meng, He; Yu, Jun; Hu, Songnian; Zhang, Heping (2007-07-18). "A complete mitochondrial genome sequence of the wild two-humped camel (Camelus bactrianus ferus): an evolutionary history of camelidae". BMC Genomics. 8 (1): 241. doi:10.1186/1471-2164-8-241. ISSN 1471-2164. PMC 1939714. PMID 17640355.
  11. Ji, R.; Cui, P.; Ding, F.; Geng, J.; Gao, H.; Zhang, H.; Yu, J.; Hu, S.; Meng, H. (2009-08-01). "Monophyletic origin of domestic bactrian camel (Camelus bactrianus) and its evolutionary relationship with the extant wild camel (Camelus bactrianus ferus)". Animal Genetics. 40 (4): 377–382. doi:10.1111/j.1365-2052.2008.01848.x. ISSN 1365-2052. PMC 2721964. PMID 19292708.
  12. Paleobiology Database - Hemiauchenia basic info
  13. Paleobiology Database - Palaeolama basic info
  14. Paleobiology Database - Blancocamelus basic info
  15. Paleobiology Database - Pleiolama basic info
  16. Paleobiology Database - Camelops basic info
  17. Paleobiology Database - Paracamelus basic info
  18. Geraads, Denis; Didier, Gilles; Barr, Andrew; Reed, Denne; Laurin, Michel (April 2020). "The fossil record of camelids demonstrates a late divergence between Bactrian camel and dromedary=Acta Palaeontologica Polonica". 65 (2): 251–260. doi:10.4202/app.00727.2020. eISSN 1732-2421. ISSN 0567-7920. Cite journal requires |journal= (help)
  19. Database - Procamelus basic info
  20. Database - Hesperocamelus basic info
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