The long neck of the giraffe is still considered a prime example of evolutionary adaptation to living conditions – perfectly developed to harvest leaves in treetops. But now an international research group is questioning this plausible thesis. In the science journal Science argues the team around the paleontologist Shi-Qi Wang of the Chinese Academy of Sciences, that among the ancestors of the modern giraffe, rivals have butted heads. This is indicated by the investigations of the remains of the previously unknown early giraffe Discokeryx xiezhi, which is said to have lived 17 million years ago.
Analysis shows that these animals had a disk-shaped headstock that bore resemblances to a helmet. According to the researchers, the fossil should have the most complex joints in the head and neck area known from mammals to date. In addition, analysis of the fossil’s enamel showed that Discokerys xiezhi may have used a different diet than other herbivores of the time.
According to Wang and his team, the unique head-neck morphology was very useful in “extreme headbutting behavior” during courtship matches between rivals. That would be an indication another theory on the origin of the long necks of giraffes.
This comes from the zoologists Robert Simmons and Lue Scheepers in 1996 and states that courtship fights in giraffes are responsible for the development of the necks. When male giraffes fight each other, they swing their necks like a slingshot to inflict damage on the opponent. Here, too, as with the leaf-eating hypothesis, the motto applies: Whoever is equipped with a longer neck has better chances – not only of winning the fight, but also of reproducing and the hereditary disposition for to pass on one’s long neck to one’s descendants.
The analysis of Discokeryx xiezhi could therefore indicate that the evolution of the giraffe’s neck may have been more complex than previously thought. Because the “headbutt skull” and the adapted neck of the giraffe’s predecessor are better optimized for a classic headbutt behavior of an animal than in any other vertebrate in evolution, writes Wang’s group in Science. The results indicate that sexual selection may be partly responsible for the length of giraffes’ necks.
“The common notion that the long necks only developed in the course of evolution because the animals used them to reach leaves in the upper part of the trees may not go far enough,” says co-author Manuela Aiglstorfer from the Natural History Museum in Mainz and the State Collection for Natural History Rhineland-Palatinate. “Perhaps this is just a side effect and combat strategy is the primary reason for the development of the long neck.”
That makes one answer to the question “Why do giraffes have such long necks?” not easier. However, the neck of a giraffe would still be a good example of evolutionary adaptation to the extreme demands of life. “Our study did not show that there was no connection between neck length and diet,” says Aiglstorfer. “But we show that in ruminants there can also be other important influences that affect the structure of the cervical spine.”