Giraffidae

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Giraffidae
Temporal range: 20–0Ma
Early Miocene - recent
Okapi.bristol.600pix.jpg
An okapi in Bristol Zoo, England
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Suborder: Ruminantia
Infraorder: Pecora
Superfamily: Giraffoidea
Family: Giraffidae
Gray, 1821
Genera

See text

The Giraffidae are ruminant artiodactyl mammals that share a common ancestor with deer and bovids. This biological family, once a diverse group spread throughout Eurasia and Africa, contains only two living members, the giraffe and the okapi. 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 species look very different on first sight, but share a number of common features, including long, dark-coloured tongues, lobed canine teeth, and horns covered in skin, called "ossicones".

Evolutionary background[edit]

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

The giraffids evolved from a group of even-toed ungulates in the early Miocene almost 25 million years ago. They formed part of a relatively late mammal diversification that also produced cattle, antelopes, and deer following a climate change that transformed subtropical woodlands into open savannah grasslands. The giraffids diversified into many now extinct forms that inhabited large parts of Eurasia and eventually spread into Africa where the only still extant forms persist. The most primitive forms had short necks and were about the size of a modern red deer, somewhat similar to the modern okapi.[1]

There are two main groups of extinct giraffids: one group with robust limb bones, the Sivatheriinae, represented by Sivatherium during the Plio-Pleistocene, and another with long and slender limb bones classified in different subfamilies; either Giraffinae and Palaeotraginae or only Giraffinae then with two tribes, Giraffini and Palaeotragini. While Giraffa and Palaeotragus can be easily attributed to the latter group, the placement of Okapia and Mitilanotherium remains disputed.[2]

Their closest fossil relatives include the deer-like palaeomerycids and the climacocerids, many genera of the latter having once been identified as giraffes themselves.

Fossil records indicate many other giraffids thrived between the Miocene era (around 20 million years ago) and the recent past. One major group of extinct giraffids, the sivatheres, had enormous, branching ossicones, and would have looked more like massive deer than giraffes.

Characteristics[edit]

Two giraffes

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. There is an especially long diastema between the front and cheek teeth. The latter are selenodont, adapted for grinding up tough plant matter. [3] Like most other ruminants, the dental formula for giraffids is:

Dentition
0.0.3.3
3.1.3.3

The two extant giraffids, the forest-dwelling okapi and the savannah-living giraffes, 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).[4]

Distribution[edit]

The two extant species 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.[5]

Behavior[edit]

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:[6]

  • 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 at 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 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 them 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-females and young-adults. Okapis are normally seen in mother-offspring pairs, although they occasionally gather around a prime food source. Giraffe are non-territorial but have ranges that can vary dramatically — 5–654 km2 (1.9–252.5 sq mi) — depending on food availability whereas okapis have individual ranges about 2.5–5 km2 (0.97–1.93 sq mi) in size.
  • Both giraffes and okapis are normally silent, but both have a range of vocalization, including coughing, snorting, moaning, hissing, whistling. It has been suggested that giraffes can communicate using infrasonic sound like elephants and blue whales.

Classification[edit]

Skeleton of Helladotherium, now extinct

Notes[edit]

  1. ^ Grzimek 2003, p. 399
  2. ^ Van der Made & Morales 2011, Classification of the Plio-Pleistocene Giraffidae
  3. ^ Pellew 1984
  4. ^ Grzimek 2003, pp. 399–400
  5. ^ Grzimek 2003, p. 401
  6. ^ Grzimek 2003, pp. 401–3

References[edit]