Giraffidae
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. Evolutionary background. 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, as shown in the cladogram below. The ancestors of pronghorn diverged from the giraffids in the Early Miocene. 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. 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. The relationship between the climacoceratids and giraffids is supported by the presence of a bilobed canine, 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. Another more commonly supported hypothesis is climacoceratids were merely the sister clade to giraffids, with sivatheres being either basal giraffids or descended from a lineage that also includes the okapi. 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. Below is the phylogenetic relationships of giraffomorphs after Solounias (2007), Sánchez et  al. (2015) and Ríos et al. (2017): Classification. Below is the total taxonomy of valid extant and fossil taxa (as well as junior synonyms which are listed in the brackets). Family Giraffidae Characteristics. The giraffe stands 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. 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. Like most other ruminants, the dental formula for giraffids is . Giraffids have prehensile tongues (specially adapted for grasping). 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 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 above the ground and their shoulder , whereas the okapi has a shoulder height of . 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. 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: 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 —  — depending on food availability, whereas okapis have individual ranges about in size.