How did giraffes develop their massive necks? The seemingly obvious explanation is that their ancestors who were able to reach higher leaves on trees were favored by natural selection. But a fossil that has just been described indicates that the process was far more complicated. One of the “protogiraffes” had a head and neck that were used for headbutting, not foraging.
The unusual animal, baptized with the scientific name discokeryx xiezhi, lived in northwest China 16.9 million years ago. Its neck was a little longer than that of a modern horse, but what really stands out in the animal’s anatomy is the presence of a kind of bony helmet, flat and disc-shaped, on top of its head. This, of course, is where the designation of the species comes from, since discokeryx means “disk-horn”.
But the flat helmet is only part of the weirdness that characterizes the mammal. The neck vertebrae have a peculiar shape and connections to each other and to the base of the skull. “It’s an adaptation directly linked to the absorption of impacts,” he explained to Sheet Shi-Qi Wang of the Institute of Vertebrate Paleontology and Paleontology at the Chinese Academy of Sciences.
Wang, along with other colleagues from China, Europe and the US, sign the description of the primitive giraffe that has just appeared in the specialist journal Science. The team also looked at the ecological context in which the animal lived, an environment that was home to other large mammals such as extinct relatives of today’s elephants, rhinos and wild boar.
One thing that was already clear from other fossil data and from comparing giraffes to their closest living relatives, the okapis, is that the giant necks of herbivores are the product of a relatively recent phase of their evolution (okapis, for example). , are much less necky). And while people only hear about the search for the tallest leaves on trees, experts have long debated the possibility that necks were selected as weapons as well.
That’s because male giraffes today use their necks in ritualized combat, something that would allow them to gain dominance positions over other males and have more opportunities to mate with females. The idea that this process was the most important came to be called, in English, the “necks for sex” hypothesis. Again, the more modest relatives of today’s giraffes provide clues to this process. “Okapis also fight using their short necks, although not as fiercely as giraffes,” says Wang.
The discovery of the Chinese fossil indicates that this process was already happening, to a large extent, in the case of the oldest relatives of giraffes and okapis. Although probably not a direct ancestor of today’s African species, the discokeryx xiezhi helps to understand how the group has evolved.
“I believe that both fighting between males and foraging at higher levels of vegetation played a role in elongating the necks, but in different ways,” ponders Wang.
A detail from the analysis of the chemical composition of the teeth of the Chinese protogiraffe is that it probably had a different diet from other herbivores in the region, taking advantage of the vegetation of more open and drier environments. This more difficult life may have increased competition between males, something that happens in other herbivores that “butt heads” with each other, such as bighorn sheep in mountain regions. In fact, according to the researchers’ calculations, the primitive giraffe was the mammal with the skull and neck most adapted to this type of combat at all times.
