|
Giraffidae is 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 members, the giraffe (the only living species of ''Giraffa'') 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 species 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. ==Evolutionary background== The giraffids evolved from a group of even-toed ungulates in the early Miocene almost . 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.〔 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. 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 that 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「giraffidae」の詳細全文を読む スポンサード リンク
|