Giraffe - Taxonomy and Evolution

Taxonomy and Evolution

The giraffe is one of only two living species of the family Giraffidae, the other being the okapi. The family was once much more extensive, with over 10 fossil genera described. Giraffids first arose 8 million years ago (mya) in south-central Europe during the Miocene epoch. The superfamily Giraffoidea, together with the family Antilocapridae (whose only extant species is the pronghorn), evolved from the extinct family Palaeomerycidae. The earliest known giraffid was the deer-like Climacoceras.

While the progressive elongation of the neck and limbs can be found throughout the giraffid lineage, it became more pronounced in genera such as Giraffokeryx, Palaeotragus (possible ancestor of the okapi), Samotherium and Bohlinia. Bohlinia entered China and northern India in response to climate change. From here, the genus Giraffa evolved and, around 7 mya, entered Africa. Further climate changes caused the extinction of the Asian giraffes, while the African ones survived and radiated into several new species. G. camelopardalis arose around 1 mya in eastern Africa during the Pleistocene. Some biologists suggest that the modern giraffe descended from G. jumae; others find G. gracilis a more likely candidate. It is believed that the main driver for the evolution of the giraffes was the change from extensive forests to more open habitats, which began 8 mya. Some researchers have hypothesized that this new habitat with a different diet, including Acacia, may have exposed giraffe ancestors to toxins that caused higher mutation rates and a higher rate of evolution.

The giraffe was one of the many species first described by Carl Linnaeus in 1758. He gave it the binomial name Cervus camelopardalis. Morten Thrane Brünnich classified the genus Giraffa in 1772. In the early 19th century, Jean-Baptiste Lamarck believed that the giraffe's long neck was an "acquired characteristic", developed as generations of ancestral giraffes strived to reach the leaves of tall trees. This theory was eventually rejected, and scientists now believe that the giraffe's neck arose through Darwinian natural selection—that ancestral giraffes with long necks thereby had a competitive advantage that better enabled them to reproduce and pass on their genes.