Wouldn’t you know it. Taught since kindergarten that the giraffe evolved a long neck to delicately dine on the leaves at the top of trees that other herbivores can’t reach – that is apparently Disney Darwinism at its most saccharine.
Apparently a key driver wasn’t dinner, it was male aggression, posits a new paleontology paper published Thursday in Science. “Head-bashing combat contributed to the evolution of giraffes’ long neck” was written by Shi-Qi Wang and Tao Deng of the Chinese Academy of Sciences with Jin Meng of the American Museum of Natural History and a long list of other colleagues
In contrast to the syrupy image of the gentle giraffe stretching ever farther skyward to sweetly sup on the tenderest of shoots in the canopy, leaving those vicious goats and greedy deer to vie over the shrubbery – the males evolved long necks in order to better beat one another over the head. Why would they do that? To get the lady.
Yes, the discovery of a previously unknown early giraffoid (aka giraffid) living 17 million years ago in China that had, essentially, a bone helmet on its head strongly supports the theory that the evolutionary impetus behind their extreme neck evolution, leading to animals that can be almost 20 feet (6 meters) tall today, was not solely a greener leaf.
With hindsight, it makes sense. Leaving extreme situations of starvation out of the equation, how far would a male go for a better salad, as opposed to the extremes they might resort to in the quest for sex?
Actually, the notion of “necks for sex,” or sexual selection driven by competition in the giraffoid set, has been making the rounds for years, the not-so-small team stresses. Other early giraffoids such as Bramatherium also have stunning skulls, literally and figuratively.
And now science has found a smoking giraffoid: Discokeryx xiezhi, which features a thick-boned skull with large disk-like headgear, a series of cervical vertebrae with extremely thickened centra and, they write, the most complicated head-neck joints in mammals known to date.
Headgear, Wang explains, refers to additional appendages grown on the head such as horns on the ox and rhino, antlers on the deer and the so-called horns of the giraffe.
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But of them all, among vertebrates D. xiezhi appears to exhibit the ultimate adaptation for head-butting – certainly when compared with extant head-butters, the team says, though it cannot speak for all vertebrates from all eras.
The animal’s name does not refer to disco as in dancing but “disco” as in round plate, and the “keryx” refers to its horn. In other words, its name isn’t meant to inspire partying but brutal battle, a behavior comparable to “neck-blowing” in male giraffes today, they write.
Whatever you think that means, it doesn’t – it means, when fighting over females, extant male giraffes steady their immense bodies on their long legs and swing their heads to deliver super-powered blows to one another with the horns on their heads.
Yes, giraffes today have up to five horns on their heads. That is what those strange protuberances on their heads are, and that is what they are for.
The theory of the evolutionary driver behind the giraffe’s extreme anatomy has gone back and forth as much as “Why do zebras have stripes?” and is equally, ultimately, unresolvable. But now the pendulum has swung back toward sex thanks to the discovery of said D. xiezhi, who lived and battled in northern China during the early Miocene.
One cannot put it better than the researchers: “Finite element analysis reveals that the enlarged atlanto-occipitalis and intercervical articulations are essential for high-speed head-to-head butting.”
They also analyzed the extinct animal’s tooth enamel to elucidate what it ate. Their conclusion is that D. xiezhi was an open-land grazer but may have been a niche feeder after all, which is relevant to their theory.
Why? Because it suggests that as the giraffids arose, their divergence may have begun with ecological drivers. The newly identified D. xiezhi emerged during a climatic paradise after protracted aridity, so the environs were packed with animals. There were at least two more types of early giraffids in the lush basin, and extending their necks could have helped them reach food in a niche other herbivores couldn’t access.
But while today only two species of giraffe still exist (both in Africa), millions of years ago there were many giraffe types that seem to have displayed more diversity in skull shape than any other ruminant groups. And that supports the thesis, the researchers explain, of interpersonal violence playing a key role in their skull evolution.
If anything, the researchers point out, their ecological positioning in a niche may have spurred the intensity of their sexual jousts, resulting in ever more extreme morphologies.
In short, the structure of D. xiezhi’s headgear and neck suggest this was one violent beast and the combination of niche eating and fighting for females resulted in neck extension, ultimately leading to the seemingly ethereal animal we know today.
In 2017, a separate set of researchers announced they had discovered the genes behind the giraffe’s elongation – which didn’t help understand the why, just the how.
Today’s giraffes only live in Africa or in zoos, but where they began to emerge is not clear.
“Early fossil giraffoids may be discovered from Africa, such as from Namibia (Orangemeryx) and Lybia (Canthumeryx and Prolibytherium), about 18 million years ago,” Wang says. But recently, the fossil giraffoids close in age were found in China, though that discovery remains unpublished at this stage, he adds. So it is not clear whether the giraffe began its journey in Africa or Eurasia. What is clear is that when they fight, you and your puny head don’t want to get in the way.