AFP, published on Friday, June 03, 2022 at 08:32
The giraffe did not always have a long neck, but it always favored 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 initial driver of giraffe neck elongation was sexual selection.
Unearthed in northern China, Discokeryx xiezhi, is the first representative of a new species, whose fossil lived about 17 million years ago, reports a study published in the journal Science this week.
This ruminant the size of a large deer had a thick bony disc at the top of the skull and a neck with formidable cervical vertebrae allowing it to withstand violent frontal shocks, according to paleontologist Shi-Qi Wang, from the Chinese Academy of Sciences, first author of the article.
This particular morphology “was most probably adapted to head-butting behavior between males”, suppose the researchers, who compare this behavior “to the fights of male giraffes with their necks”. The latter – the current species – engage in struggles for domination by swinging their head, endowed with small horns, against the adversary.
The discovery of Chinese paleontologists pours a decisive piece into a debate as old as that of paleontology: why does the giraffe have such 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 recent and much disputed, the other theory postulates that a long and powerful neck influences the outcome of fights between males, and has therefore favored its growth.
– Sexual competition –
The study by Shi-Qi Wang and his colleagues agrees with this last thesis: this kind of fighting is “probably the first reason why giraffes developed a long neck”, which then provided them with an advantage for grazing on tall foliage.
“It is a perfect example of + exaptation +, that is to say of an advantage provided by an organ which will later prove useful for another use”, explains to AFP the paleontologist Grégoire Metais, of the National Museum of Natural History, which salutes a “very beautiful study”.
According to him, giraffids have embarked on a “race ahead” for a long and reinforced neck. This “shows once again that sexual competition is one of the engines of evolution, which leads to morphological innovations that can be used for other purposes”.
In the case of Discokeryx xiezhi, its morphology represented “the most optimal adaptation for headbutting, when compared with current species” engaging in this practice, according to the study.
As proof, computer modeling of the impact of headbutts, applied to other combative ruminants, such as the muskox, suggests that the “very special morphology of the head and neck of Discokeryx xiezhi was linked to intense practice headbutt”. And that this morphology gave him an incomparable ability to “absorb the energy of the shock and protect his brain”.
The study also clearly establishes that this fossil was a giraffoid, which appeared about 20 million years ago, of which the only two species still existing are the giraffe and the okapi.
But then, why didn’t Discokeryx xiezhi also develop a long neck? First, because he didn’t need it: he lived through a remarkable episode of the Miocene, which saw a marked warming of the climate, allowing him to graze to his heart’s content. Then, because it was only “the beginning of the history of girafids”, recalls Mr. Metais. And that of the growth of their long necks.