Camelidae
Temporal range: Middle Eocene – Holocene
A Bactrian camel walking in the snow
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Suborder: Tylopoda
Superfamily: Cameloidea
Family: Camelidae
Gray, 1821
Type genus
Camelus
Subfamilies
Current range of camelids, all species

Camelids are members of the biological family Camelidae, the only currently living family in the suborder Tylopoda. The seven 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 Artiodactyla, along with species including whales, pigs, deer, cattle, and antelopes.

Characteristics

Camelid feet lack functional hooves, with 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. As in ruminants, the upper incisors are largely absent and are replaced by a dental pad consisting of connective tissue covered with epithelium.[3] 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 have adapted to the steep and rocky terrain by adjusting the pads on their toes to maintain grip.[4] 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.[5] Many fossil camelids were unguligrade and probably hooved, in contrast to all living species.[6]

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.[7] 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.[8]

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.[9]

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)
Dromedary
or
Arabian camel

(Camelus dromedarius)

 South Asia and Middle East
(entirely domesticated)		 300 to 600 kg (660 to 1,320 lb)
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) 130 to 200 kg (290 to 440 lb)
Guanaco

(Lama guanicoe)

 South America about 90 to 120 kg (200 to 260 lb)
Alpaca

(Lama pacos)

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

(Lama vicugna)

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

Evolution

Camelid
Lamini
Lama

L. glama

L. guanicoe

V. vicugna

V. pacos

Camelini
Camelus

C. bactrianus

C. dromedarius

†Camelops
⊞

C. kansanus

C. hesternus

C. minodokae

⊟
A family tree indicating different species within the Camelidae family[10]
A dymaxion map of the biogeographic distribution of Camelidae species:
  Tertiary distribution
  Present-day 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 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.[6][11]

The family diversified and prospered, with the two living tribes, the Camelini and Lamini, diverging in the late early Miocene about 16 million years ago, but remained confined to the North American continent until about seven million years ago, when Paracamelus crossed the Bering land bridge into Eurasia, giving rise to the modern camels, and about three 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 - llamas, alpacas, guanacos, and vicuñas. Camelids were domesticated by early Andean peoples,[12] 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.[6]

Whether the wild Bactrian camel (Camelus ferus) is a distinct species or a subspecies (C. bactrianus ferus) is still debated.[13][14] The divergence date is 0.7 million years ago, long before the start of domestication.[14]

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[15])

Lama guanicoe

Lama glama

Lama pacos

Lama vicugna

 Lama
Palaeolama
 (1.8 to 0.012 mya[16])
Blancocamelus
 (1.8 to 0.3 mya[17])
Pleiolama
 (10.3 to 2.588 mya[18])
Lamini
Camelops
 (2.588 to 0.012 mya[19])
Paracamelus
 (11.608 to 0.781 mya[20][21])

Bactrian camel

Dromedary

 Camelus
Procamelus
 (15.97 to 5.332 mya[22])
Camelini
Hesperocamelus
 (20.43 to 15.97 mya[23])
  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
Aguascalientia[24] Earliest Miocene A small, primitive, narrow-snouted floridatraguline camel
Camelops Pliocene-Pleistocene Large, with true camel feet, 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
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
Stevenscamelus[24] Late Eocene Long-snouted primitive relative of Floridatragulus
Titanotylopus Miocene-Pleistocene Tall, humped, true camel feet

References

  1. 1 2 Clutton-Brock, Juliet (1987). A Natural History of Domesticated Mammals. Cambridge University Press. p. 208. ISBN 978-0-521-34697-9.
  2. 1 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. ↑ Niehaus, Andrew (2022), "Tooth Root Abscess", Comparative Veterinary Anatomy, Elsevier, pp. 1013–1019, doi:10.1016/b978-0-323-91015-6.00089-3, ISBN 978-0-323-91015-6, retrieved 2023-10-29
  4. ↑ Franklin, William (1984). Macdonald, D. (ed.). The Encyclopedia of Mammals. New York: Facts on File. pp. 512–515. ISBN 978-0-87196-871-5.
  5. ↑ Clemente, Christofer J.; Dick, Taylor J. M.; Glen, Christopher L.; Panagiotopoulou, Olga (2020-03-02). "Biomechanical insights into the role of foot pads during locomotion in camelid species". Scientific Reports. 10 (1): 3856. Bibcode:2020NatSR..10.3856C. doi:10.1038/s41598-020-60795-9. ISSN 2045-2322. PMC 7051995. PMID 32123239.
  6. 1 2 3 Savage, RJG; Long, MR (1986). Mammal Evolution: an illustrated guide. New York: Facts on File. pp. 216–221. ISBN 978-0-8160-1194-0.
  7. ↑ Janis, Christine M.; Theodor, Jessica M.; Boisvert, Bethany (2002-03-14). "Locomotor evolution in camels revisited: a quantitative analysis of pedal anatomy and the acquisition of the pacing gait". Journal of Vertebrate Paleontology. 22 (1): 110–121. doi:10.1671/0272-4634(2002)022[0110:LEICRA]2.0.CO;2. ISSN 0272-4634. S2CID 86174860.
  8. ↑ 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.
  9. ↑ Wild Bactrian Camels Critically Endangered, Group Says National Geographic, 3 December 2002
  10. ↑ "Animal Diversity Web." ADW: Camelidae: CLASSIFICATION. N.p., n.d. Web. 09 June 2017.
  11. ↑ 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.
  12. ↑ Moore, Katherine M. (2016). "Early Domesticated Camelids in the Andes". In Capriles, Jose M.; Tripcevich, Nicholas (eds.). The Archaeology of Andean Pastoralism. University of New Mexico Press. ISBN 978-0-8263-5702-1.
  13. ↑ 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.
  14. 1 2 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.
  15. ↑ Paleobiology Database - Hemiauchenia basic info
  16. ↑ Paleobiology Database - Palaeolama basic info
  17. ↑ Paleobiology Database - Blancocamelus basic info
  18. ↑ Paleobiology Database - Pleiolama basic info
  19. ↑ Paleobiology Database - Camelops basic info
  20. ↑ Paleobiology Database - Paracamelus basic info
  21. ↑ 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". Acta Palaeontologica Polonica. 65 (2): 251–260. doi:10.4202/app.00727.2020. eISSN 1732-2421. ISSN 0567-7920.
  22. ↑ Database - Procamelus basic info
  23. ↑ Database - Hesperocamelus basic info
  24. 1 2 Prothero, D.R.; Beatty, B.L.; Marriott, K. (September 2023). "Systematics of the long-nosed Floridatraguline camels (Artiodactyla: Camelidae)" (PDF). Fossil Record. 9 (94): 533–545. Retrieved 18 December 2023.
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