Giraffidae
Temporal range: 20–0 Ma Early Miocene - recent
An okapi in Bristol Zoo, England
Masai giraffe (G. tippelskirchi) at the Mikumi National Park, Tanzania
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Superfamily: Giraffoidea
Family: Giraffidae
Gray, 1821
Subfamilies

The Giraffidae are a family of ruminant artiodactyl mammals that share a common ancestor with cervids and bovids. This family, once a diverse group spread throughout Eurasia and Africa, presently comprises only two extant genera, the giraffe (one or more species of Giraffa, depending on taxonomic interpretation) and the okapi (the only known species of Okapia). Both are confined to sub-Saharan Africa: the giraffe to the open savannas, and the okapi to the dense rainforest of the Congo. The two genera look very different on first sight, but share a number of common features, including a long, dark-coloured tongue, lobed canine teeth, and horns covered in skin, called ossicones.

Taxonomy

Image Genus Living species
Okapia
Giraffa

Evolutionary background

Shansitherium and Palaeotragus microdon, two giraffids from the Miocene of Asia
Shansitherium and Palaeotragus microdon, two giraffids from the Miocene of Asia

The giraffids are ruminants of the clade Pecora. Other extant pecorans are the families Antilocapridae (pronghorns), Cervidae (deer), Moschidae (musk deer), and Bovidae (cattle, goats and sheep, wildebeests and allies, and antelopes). The exact interrelationships among the pecorans have been debated, mainly focusing on the placement of Giraffidae, but a recent large-scale ruminant genome sequencing study suggests Antilocapridae are the sister taxon to Giraffidae.[1] The ancestors of pronghorn diverged from the giraffids in the Early Miocene.[1] This was in part of a relatively late mammal diversification following a climate change that transformed subtropical woodlands into open savannah grasslands.

The fossil record of giraffids and their stem-relatives is quite intensive, with fossil of these taxa include Gelocidae, Palaeomerycidae, Prolibytheridae, and Climacoceratidae.[2][3] It is thought the palaeomerycids is the ancestral group that given rise to the prolibytherids, climacoceratids and the giraffids, all three forming a clade of pecorans known as Giraffomorpha.[2][4] The relationship between the climacoceratids and giraffids is supported by the presence of a bilobed canine,[2] and have been postulated into two hypotheses. One is the climacoceratids were the ancestors of the sivatheres, as both groups were large, deer-like giraffoids with branching antler-like ossicones, while an extinct basal group of giraffoids, canthumerycines, evolved into the ancestors of Giraffidae.[3] Another more commonly supported hypothesis is climacoceratids were merely the sister clade to giraffids, with sivatheres being either basal giraffids[2] or descended from a lineage that also includes the okapi.[5] While the current range of giraffids today is in Africa, the fossil record of the group has shown this family was once widespread throughout of Eurasia.[2][3][5]

Below is the phylogenetic relationships of giraffomorphs after Solounias (2007),[2] Sánchez et al. (2015)[4] and Ríos et al. (2017):[5]

Giraffomorpha

Palaeomerycidae

Giraffoidea

Prolibytheridae

Climacoceratidae

Giraffidae

†Canthumerycinae[a]

†Giraffokerycinae

†Bohlininae

Giraffinae

†Palaeotraginae

Okapiinae

†Samotheriinae[b]

†Sivatheriinae

Classification

Skeletal illustration of Helladotherium, now extinct
Skeletal illustration of Helladotherium, now extinct
Skeletal mount of Palaeotragus on display at the Tianjin Natural History Museum.
Skeletal mount of Palaeotragus on display at the Tianjin Natural History Museum.
Skeletal mount of Shansitherium tafeli on display at the Beijing Museum of Natural History.
Skeletal mount of Shansitherium tafeli on display at the Beijing Museum of Natural History.

Below is the total taxonomy of valid extant and fossil taxa (as well as junior synonyms which are listed in the brackets).

Family Giraffidae J.E.Gray, 1821

Characteristics

Two giraffes
Two giraffes

The giraffe stands 5–6 m (16–20 ft) tall, with males taller than females. The giraffe and the okapi have characteristic long necks and long legs. Ossicones are present on males and females in the giraffe, but only on males in the okapi.[6]

Giraffids share many common features with other ruminants. They have cloven hooves and cannon bones, much like bovids, and a complex, four-chambered stomach. They have no upper incisors or upper canines, replacing them with a tough, horny pad. An especially long diastema is seen between the front and cheek teeth. The latter are selenodont, adapted for grinding up tough plant matter.[7] Like most other ruminants, the dental formula for giraffids is 0.0.3.33.1.3.3. Giraffids have prehensile tongues (specially adapted for grasping).[8]

The extant giraffids, the forest-dwelling okapi and the savannah-living giraffe, have several features in common, including a pair of skin-covered horns, called ossicones, up to 15 cm (5.9 in) long (absent in female okapis); a long, black, prehensile tongue; lobed canine teeth; patterned coats acting as camouflage; and a back sloping towards the rear. The okapi's neck is long compared to most ruminants, but not nearly so long as the giraffe's. Male giraffes are the tallest of all mammals: their horns reach 5.5 m (18 ft) above the ground and their shoulder 3.3 m (11 ft), whereas the okapi has a shoulder height of 1.7 m (5 ft 7 in).[9]

Distribution

The two extant genera are now confined to sub-Saharan Africa. The okapi is restricted to a small range in the northern rainforest of the Democratic Republic of Congo. Although the range of the giraffe is considerably larger, it once covered an area twice the present size — all parts of Africa that could offer an arid and dry landscape furnished with trees.[9]

Behavior

The social structure and behavior is markedly different in okapis and giraffes, but although little is known of the okapi's behavior in the wild, a few things are known to be present in both species:[9]

Giraffes are sociable, where as okapis live mainly solitary lives. Giraffes temporarily form herds of up to 20 individuals; these herds can be mixed or uniform groups of males and females, young and adults. Okapis are normally seen in mother-offspring pairs, although they occasionally gather around a prime food source. Giraffe are not territorial, but have ranges that can dramatically vary between — 5 and 654 km2 (1.9 and 252.5 sq mi) — depending on food availability, whereas okapis have individual ranges about 2.5–5 km2 (0.97–1.93 sq mi) in size.

Notes

  1. ^ A grade of giraffids.
  2. ^ A paraphyletic grade of palaeotragines ancestral to Sivatheriinae.

References

  1. ^ a b Chen, L.; Qiu, Q.; Jiang, Y.; Wang, K. (2019). "Large-scale ruminant genome sequencing provides insights into their evolution and distinct traits". Science. 364 (6446): eaav6202. Bibcode:2019Sci...364.6202C. doi:10.1126/science.aav6202. PMID 31221828.
  2. ^ a b c d e f Solounias, N. (2007). "Family Giraffidae". In Prothero, D.R.; Foss, S.E. (eds.). The Evolution of Artiodactyls. The Johns Hopkins University Press. pp. 257–277. ISBN 9780801887352.
  3. ^ a b c Skinner, J.; Mitchell, G. (2011). "Family Giraffidae (Giraffe and Okapi)". In Wilson, D.E.; Mittermeier, R.A. (eds.). Handbook of the Mammals of the World – Volume II. Barcelona: Lynx Ediciones. pp. 788–802. ISBN 978-84-96553-77-4.
  4. ^ a b Sánchez, Israel M.; Cantalapiedra, Juan L.; Ríos, María; Quiralte, Victoria; Morales, Jorge (2015). "Systematics and Evolution of the Miocene Three-Horned Palaeomerycid Ruminants (Mammalia, Cetartiodactyla)". PLOS ONE. 10 (12): e0143034. Bibcode:2015PLoSO..1043034S. doi:10.1371/journal.pone.0143034. PMC 4668073. PMID 26630174.
  5. ^ a b c Ríos, M.; Sánchez, I.M.; Morales, J. (2017). "A new giraffid (Mammalia, Ruminantia, Pecora) from the late Miocene of Spain, and the evolution of the sivathere-samothere lineage". PLOS ONE. 12 (11): e0185378. Bibcode:2017PLoSO..1285378R. doi:10.1371/journal.pone.0185378. PMC 5665556. PMID 29091914.
  6. ^ Dagg, A. I. (1971). "Giraffa camelopardalis" (PDF). Mammalian Species. 5 (5): 1–8. doi:10.2307/3503830. JSTOR 3503830.
  7. ^ Pellew, Robin (1984). MacDonald, D. (ed.). The Encyclopedia of Mammals. New York: Facts on File. pp. 534–541. ISBN 978-0-87196-871-5.
  8. ^ Kingdon, Jonathan (2013). Mammals of Africa (1st ed.). London: A. & C. Black. pp. 95–115. ISBN 978-1-4081-2251-8.
  9. ^ a b c Grzimek, Bernhard (2003). Hutchins, Michael; Kleiman, Devra G; Geist, Valerius; et al. (eds.). Grzimek's Animal Life Encyclopedia, Vol 15, Mammals IV (2nd ed.). Farmington Hills, MI: Gale Group. ISBN 978-0-7876-5362-0.