Antitypes, Ancestors, and the Origin of Modern Giraffes

Against the odds, over a period of 8 million years the genetic material in small gazelle-like Canthumerycids transformed by natural selection into modern long-legged, long-necked giraffes, Giraffa camelopardalis. How did that happen? The 8 million-year-long evolutionary gap between Canthumerycids and giraffes, during which the astonishing morphophysiological changes occurred, is filled by three ancestral species of Paleotragine giraffids—Giraffokeryx, Paleotragus, and Samotherium—that lived in southern central Europe, with each making small but significant evolutionary contributions. While all had elongated necks, their necks were never more than half the length of modern giraffes. All, though, had long legs. Long necks arose in Bohlinia, a unique species that evolved from the Paleotragine genetic pool. Bohlinia migrated to Asia and gave rise to Indian and Chinese giraffes, and also into North Africa. Relatively quickly the Indo-Asian giraffes became extinct. In Africa the giraffe lineage that produced modern giraffes began with the evolution of Giraffa jumae from Bohlinia about 6 million years ago. G. jumae was the origin of three ancestors of modern giraffes—G. stillei, G. gracilis, and G. pygmaea—that made their appearance in East Africa around 3 million years ago. Their appearance then was a consequence of major episodes of climate change. From their genetic pool, modern giraffes, G. camelopardalis, emerged 1 million years ago.