Overview

Brief Summary

Diversity of Living Giraffidae (Giraffe and Okapi)

The family Giraffidae is one of a number of families in the mammal order Artiodactyla (even-toed ungulates). There are just two living species, the Giraffe (Giraffa camelopardalis) and the Okapi (Okapia johnstoni). Giraffes occur in a patchy distribution in savannas across parts of sub-Saharan Africa. Okapi are endemic to the forests of DR Congo.

Giraffes are the tallest mammals in the world. At birth, they stand between 1.5 and 1.8 m; at maturity, females may reach 4.5 to 5 m and males 5 to 6 m. Body mass at birth is around 100 kg (less in captive animals). Body mass of mature females can reach 1100 kg and mature males can reach 1500 kg. Giraffes have very long necks although, like nearly all other mammals, they have just seven cervical vertebrae—their cervical vertebrae are very long (as are their lower leg bones). The neck is held upright when a Giraffe walks, but stretched forward when it is running or moving uphill. A variety of morphological and physiological adaptations related to blood flow prevent problems from arising when the Giraffe lowers and raises its neck (e.g., to drink).

Okapi are secretive forest-dwellers that have been known to science only since 1901 (although they were already familiar to local indigenous people). They share some evident similarities with Giraffes, but bear an overall resemblance to some of the larger antelope species. In contrast to Giraffes, Okapi females are taller and more massive than males.

Ecology and Behavior

The structure of a Giraffe herd is fluid and the same individuals rarely stay together for long. Females and young are usually found in a herd together; younger males may form bachelor herds. Mature bulls are generally solitary, although they may join a temporary harem of females. Unlike Giraffes, which are not territorial, Okapi of both sexes hold territories.

The Giraffe is one of just two ungulate species known to have a gestation period longer than a year (450 days). In the wild, females become mature at 4 to 5 years. When her young is born (usually just one), a female may produce 10 liters of milk each day. Giraffe milk is richer in fat and protein than that of dairy cows. The gestation period for Okapi is shorter than that of Giraffes, around 14 months.

Giraffes are almost exclusively browsers. Acacia leaves are a major component of Giraffe diets, as are Combretum trees. Giraffes favor food plants rich in calcium and phosphorus, which are important in building their large skeletons. Giraffes use their powerful prehensile tongues to pull shoots and twigs into their mouths, where leaves are stripped off between the lower teeth and the upper dental pad. The tongue is very rough and Giraffes are reported to munch fully hardened thorns, although they prefer to feed on vegetation without thorns. Okapi feed on plants in their forest habitat. They use their prehensile tongues to strip leaves from branches and bring them into the mouth. An Okapi's tongue is so long it can wash its eyelids and ears with it.

Although Giraffes are generally able to survive on the water content of their food, when water is accessible they tend to come to drink at intervals of three days or less. Drinking Giraffes, with head lowered and forelegs splayed, are particularly vulnerable to predators.

Within historical times, Giraffes were widely distributed throughout Africa, but never in the tropical rainforest of the Congo River, which is home to the Okapi. The Giraffe's current distribution is far smaller than it once was and very patchy, but Giraffes can be found in a range of dry savanna habitats, from scrub to woodland, and are closely associated with acacia thornveld, as well as deciduous woodland tree species.

Male Giraffes often fight, striking one another with their necks and heads. These bouts are generally highly ritualized in young males, causing no injury, but when they occur between mature bulls they tend to be more serious. Although it has been suggested that the long necks of Giraffes are a product of sexual selection in males, with longer and heavier necks being favored in the struggle among males for mating opportunities, necks of both sexes grow in length and mass at similar rates.

Communication among Giraffes seems to involve mainly vision and olfaction.

Conservation Status of Giraffes and Okapi

Although the Giraffe is listed on the IUCN Red List as Least Concern, it has declined dramatically over parts of its range, especially in West Africa. It is now extinct in many countries where it once occurred, including Burkina Faso, Eritrea, Guinea, Malawi, Mauritania, and Senegal (and possibly Mali and Nigeria). Some named subspecies are in trouble as well. The Okapi is listed by IUCN as Near Threatened, although given its secretive nature, an accurate population assessment is difficult. Habitat loss is a serious threat. Okapi were once present  in Uganda (and possibly elsewhere) but are no longer believed to occur anywhere outside DR Congo.

  • Skinner, J.D. and G. Mitchell. 2011. Family Giraffidae (Giraffe and Okapi). Pp. 788-802. in: Wilson, D.E. & Mittermeier, R.A., eds. Handbook of the Mammals of the World. Volume 2. Hoofed Mammals. Lynx Edicions, Barcelona.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

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Specimen Records: 7
Specimens with Sequences: 15
Specimens with Barcodes: 7
Species: 3
Species With Barcodes: 3
Public Records: 7
Public Species: 3
Public BINs: 2
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Wikipedia

Giraffidae

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]

  • 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 0-7876-5362-4. 
  • Pellew, Robin (1984). MacDonald, D., ed. The Encyclopedia of Mammals. New York: Facts on File. pp. 534–541. ISBN 0-87196-871-1. 
  • Van der Made, J.; Morales, J. (2011). "Mitilanotherium inexpectatum (Giraffidae, Mammalia) from Huélago (Lower Pleistocene; Guadix-Baza Basin, Granada, Spain) — Observations on a Peculiar Biogeographic Pattern". Estudios Geologicos 67: 613–27. doi:10.3989/egeol.40560.209. Retrieved June 2013. 
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