The giraffe does not always have a long neck, but it always favors headbutting to defend its position, as evidenced by the discovery of a fossil specimen of a giraffoid with a real skull shield.
This finding supports the thesis that the first cause of giraffe neck elongation is sexual selection.
Excavated in northern China, the fossil of Discokeryx xiezhi belongs to a species unknown until now, that lived 17 million years ago, the report of a study published in the journal Science.
This ruminant the size of a deer has a thick bony disc at the top of the skull and a neck with heavy cervical vertebrae that allow it to withstand violent frontal shocks, according to paleontologist Shi-Qi Wang. , from the Chinese Academy of Sciences, first. author of the article.
This morphology is likely to be adapted to head-butting behaviors between mensuppose the researchers, comparing this behavior in battles of male giraffes using their necks. The latter – the current species – engage in struggles for domination by swinging their heads, equipped with small horns, against the enemy with full force.
The discovery by Chinese paleontologists is a decisive part in a debate as old as paleontology: why does the giraffe have a long neck?
Paleontologists have long defended the thesis of ecological advantage, according to which this long neck gave its holder a decisive advantage in reaching high foliage. More recently and highly controversial, another theory postulates that a long and strong neck influences the outcome of fights between men, and therefore favors its growth.
Sexual competition
The study of Shi-Qi Wang and his colleagues agrees with this last thesis: this type of conflict is perhaps the first reason why giraffes had long neckswhich then gave them an advantage for grazing the leaves above.
This is a perfect example of exaptation, that is to say an advantage given by an organ that will eventually prove useful for another use.explained to AFP paleontologist Grégoire Metais, of the National Museum of Natural History, saluting a very good study.
According to him, the giraffids started with a career forward for a long and reinforced neck. yun again showing that sexual competition is one of the engines of evolution, leading to morphological innovation that can be used for other purposes..
In the case of Discokeryx xiezhirepresents its morphology the optimal adaptation for headbutting, compared to current species engaged in this training, according to the study.
As proof, computer modeling of the effect of headbutts, applied to other ruminant defenses, such as muskox, suggests that very special morphology of the head and neck of Discokeryx xiezhI was linked to an intense headbutting practice. And that this morphology gave him unparalleled ability absorb impact energy and protect his brain.
The study also clearly establishes that this fossil is a girafoid, which appeared about 20 million years ago, of which the only two species that still exist are the giraffe and the okapi.
But why Discokeryx xiezhi did he not also have a long neck? First because he didn’t need it: he lived in a wonderful Miocene period, which saw the clear warming of the climate, allowing him to eat to his heart’s content. Then, because it is just the beginning of the history of giraffes, recalls Mr. Metais. And the growth of their long necks.
Source: Radio-Canada
