The okapi, also known as the forest giraffe, Congolese giraffe and zebra giraffe, is an artiodactyl mammal that is endemic to the northeast Democratic Republic of the Congo in central Africa. However, non-invasive genetic identification has suggested that a population has occurred south-west of the Congo River as well. It is the only species in the genus Okapia. Although the okapi has striped markings reminiscent of zebras, it is most closely related to the giraffe. The okapi and the giraffe are the only living members of the family Giraffidae.
Artiodactyls are mammals belonging to the order Artiodactyla. Typically, they are ungulates which bear weight equally on two of their five toes: the third and fourth, often in the form of a hoof. The other three toes are either present, absent, vestigial, or pointing posteriorly. By contrast, most perissodactyls bear weight on an odd number of the five toes. Another difference between the two is that many artiodactyls digest plant cellulose in one or more stomach chambers rather than in their intestine as perissodactyls do. The advent of molecular biology, along with new fossil discoveries, found that cetaceans fall within this taxonomic branch, being most closely related to hippopotamuses. Some modern taxonomists thus apply the name Cetartiodactyla to this group, while others opt to include cetaceans within the existing name of Artiodactyla. Some researchers use "even-toed ungulates" to exclude cetaceans and only include terrestrial artiodactyls, making the term paraphyletic in nature.
The Giraffidae are a family of ruminant artiodactyl 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 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 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.
Proconsul is an extinct genus of primates that existed from 21 to 17 million years ago during the Miocene epoch. Fossil remains are present in Eastern Africa including Kenya and Uganda. Four species have been classified to date: P. africanus, P. gitongai, P. major and P. meswae. The four species differ mainly in body size. Environmental reconstructions for the Early Miocene Proconsul sites are still tentative and range from forested environments to more open, arid grasslands.
Ekembo nyanzae, originally classed as a species of Proconsul, is a species of fossil primate first discovered by Louis Leakey on Rusinga Island in 1942, which he published in Nature in 1943. It is also known by the name Dryopithecus africanus. A joint publication of Wilfrid Le Gros Clark and Louis Leakey in 1951, "The Miocene Hominoidea of East Africa", first defines Proconsul nyanzae. In 1965 Simons and Pilbeam replaced Proconsul with Dryopithecus, using the same species names.
Pecora is an infraorder of even-toed hoofed mammals with ruminant digestion. Most members of Pecora have cranial appendages projecting from their frontal bones; only two extant genera lack them, Hydropotes and Moschus. The name "Pecora" comes from the Latin word pecus, which means "cattle". Although most pecorans have cranial appendages, only some of these are properly called "horns", and many scientists agree that these appendages did not arise from a common ancestor, but instead evolved independently on at least two occasions. Likewise, while Pecora as a group is supported by both molecular and morphological studies, morphological support for interrelationships between pecoran families is disputed.
Prolibytherium is an extinct genus of prolibytheriid artiodactyl ungulate native to Middle Miocene North Africa and Pakistan, from around 16.9 to 15.97 million years ago. Fossils of Prolibytherium were found in the Marada Formation of Libya, Vihowa Formation of Pakistan, and the Moghara Formation of Egypt.
Sivatherium is an extinct genus of giraffids that ranged throughout Africa to the Indian subcontinent. The species Sivatherium giganteum is, by weight, one of the largest giraffids known, and also one of the largest ruminants of all time.
Ossicones are columnar or conical skin-covered bone structures on the heads of giraffes, male okapi, and some of their extinct relatives. Ossicones are distinguished from the superficially similar structures of horns and antlers by their unique development and a permanent covering of skin and fur.
Climacoceratidae is a family of superficially deer-like artiodactyl ungulates which lived in the Miocene epoch in Africa. They are close to the ancestry of giraffes, with some genera, such as Prolibytherium, originally classified as giraffes.
Giraffokeryx is an extinct genus of medium-sized giraffids known from the Miocene of the Indian subcontinent and Eurasia. It is distinguished from other giraffids by the four ossicones on its head; one pair in front of the eyes on the anterior aspect of the frontal bone and the other behind the eyes in the frontoparietal region overhanging the temporal fossae. It has a brachydont dentition like in other giraffids and its legs and feet are of medium length. Giraffokeryx is considered monotypic by most authors, in the form of G. punjabiensis, but other species have been assigned to the genus:
Honanotherium is a genus of extinct giraffid from the late Miocene of Henan Province, China, and East Azerbaijan Province, northwestern Iran. It was closely related to Bohlinia and was once thought to be ancestral to the modern giraffe. The living animal would have resembled a modern giraffe, but was somewhat shorter, with more massive ossicones.
Bramatherium is an extinct genus of giraffids that ranged from India to Turkey in Asia. It is closely related to the larger Sivatherium.
The Palaeomerycidae is an extinct family of Neogene ruminants belonging to the infraorder Pecora. Palaeomerycids lived in Europe and Asia exclusively during the Miocene, coevolving with cervids, bovids, moschids, and tragulids there as part of a dramatic radiation of ruminants by the early Miocene.
Samotherium is an extinct genus of Giraffidae from the Miocene and Pliocene of Eurasia and Africa. Samotherium had two ossicones on its head, and long legs. The ossicones usually pointed upward, and were curved backwards, with males having larger, more curved ossicones, though in the Chinese species, S. sinense, the straight ossicones point laterally, not upwards. The genus is closely related to Shansitherium. Fossil evidence suggests that Samotherium had a rounded muzzle, which would suggest a grazing lifestyle and a habitat composed of grassland. One common predator of this animal was the Amphimachairodus.
Injanatherium is an extinct genus of giraffids from the Miocene of Iraq, Saudi Arabia, and Pakistan. Species of Injanatherium had at least two pairs of long, wing-like ossicones that emanated laterally above the orbits.
Giraffoidea is a superfamily that includes the families Climacoceratidae, Prolibytheriidae, and Giraffidae. The only extant members in the superfamily are the giraffes and okapi. The Climacoceratidae are also placed in the superfamily, but were originally placed within the family Palaeomerycidae.
Palaeotragus is a genus of very large, primitive, okapi-like giraffids from the Miocene of Africa and Eurasia.
Micropithecus is an extinct genus of primates that lived in East Africa about 19 to 15 million years ago, during the early Miocene. The genus and its type species, Micropithecus clarki, were first scientifically described in 1978.
Giraffomorpha is a clade of pecoran ruminants containing the superfamilies Palaeomerycoidea (Palaeomerycidae) and Giraffoidea, of which the giraffe and okapi of the Giraffidae are the only extant members of the once-diverse clade as a result of a decline in diversity after the Miocene as a result of declines in temperatures. The clade is defined by the presence of ossicones, suggesting that the feature was developed as a result of basal, related evolutions between the two superfamilies rather than as an instance of parallel evolution. Giraffomorpha is also characterized by a lack of articular fossettes (hollows) in metatarsal bones III-IV.
