The Giraffidae are a family of ruminantartiodactyl mammals that share a common ancestor with deer and bovids. This family, once a diverse group spread throughout Eurasia and Africa, presently comprises only two extant genera, the giraffe (between one and eight, usually four, 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.
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 subtropicalwoodlands into open savannahgrasslands.
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 that the palaeomerycids, prolibytherids, climacoceratids and the giraffids all form 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]
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]
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]
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]
They have an ambling gait similar to camels, with their weight supported alternately by their left and right legs, while their necks maintain balance. Giraffes can run up to 60 km/h (37 mph) this way and are documented to have covered 1,500 km (930 mi) in the Sahel during the dry season.
The dominance hierarchy, which has been well-documented among giraffes, has also been seen among captive okapis. An adult giraffe head can weigh 30 kg (66 lb), and if necessary, male giraffes establish a hierarchy among themselves by swinging their heads at each other, horns first, a behavior known as "necking". A subordinate okapi signals submission by placing its head and neck on the ground.
Giraffes are sociable, whereas 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.
Giraffes and okapis are normally silent, but both have a range of vocalizations, including coughing, snorting, moaning, hissing, and whistling. Giraffes have been suggested to be able to communicate using infrasonic sounds like elephants and blue whales.
^ abcdefSolounias, N. (2007). "Family Giraffidae". In Prothero, D.R.; Foss, S.E. (eds.). The Evolution of Artiodactyls. The Johns Hopkins University Press. pp. 257–277. ISBN9780801887352.
^ abcSkinner, 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. ISBN978-84-96553-77-4.
^Kingdon, Jonathan (2013). Mammals of Africa (1st ed.). London: A. & C. Black. pp. 95–115. ISBN978-1-4081-2251-8.
^ abcGrzimek, 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. ISBN978-0-7876-5362-0.
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