Giraffes may be long-necked for fights, not just food

Giraffes may be long-necked for fights, not just food

Since the days of Charles Darwin, the long necks of giraffes have been a textbook example of evolution. The theory goes that as giraffe ancestors competed for food, those with longer necks were able to reach higher leaves, getting a leg – or neck – up over shorter animals.

But a bizarre prehistoric giraffe relative reveals that, in addition to foraging, fighting may have driven early neck evolution. In a study published Thursday in Science, a team of paleontologists described Discokeryx xiezhi, a giraffe ancestor, as having helmet-like headgear and bulky neck vertebrae. Discokeryx was adapted to absorb and deliver skull-cracking collisions to woo mates and vanquish rivals.

“It shows that giraffe evolution is not just elongating the neck,” said Jin Meng, a paleontologist at the American Museum of Natural History and co-author of the new study. “Discokeryx goes in a totally different direction.”

Meng and his colleagues discovered the fossils in an outcrop of rock in northwestern China called the Junggar Basin. Around 17 million years ago, this area was an expanse of savannas and forests that were home to an array of large mammals like shovel-tusked elephants, short-horned rhinoceroses and burly bear dogs.

While exploring this bonebed in 1996, Meng stumbled across a hunk of skull. He could tell it was a mammalian braincase, but the top was flattened like an iron press. Without more of the animal’s skeleton, Meng and his colleagues referred to it as the “strange beast.”

In recent years, more fossilized material – such as teeth and jaw fragments – began to surface in the Junggar Basin, helping identify the beast. According to Meng, both the creature’s teeth and inner ear structure were reminiscent of modern giraffes. They determined that Discokeryx was one of the earliest graffids, an ancestral group of hoofed mammals that gave rise to giraffes. Discokeryx likely resembled an okapi, a forest-dwelling cousin of modern giraffes.

Its neck was long, but nothing like a modern giraffe’s, and researchers have yet to pinpoint how the animal’s anatomical features connect with its counterparts today. Still, Discokeryx was distinguished by its bizarre skull. According to Shi-Qi Wang, a paleontologist at the Chinese Academy of Sciences and another author of the study, the saucerlike bone capping the animal’s head was probably sheathed in keratin. As the keratin grew, older layers were pushed out, forming a thick dome. This made Discokeryx look like it was wearing a poorly fitting bicycle helmet.

Its bony cap was anchored to dense vertebrae in the animal’s neck. When it came time to butt heads, the vertebrae locked together into a column perpendicular to the head dome, forming a literal battering ram.

Head-butting is an ancient and widespread form of conflict resolution. Dinosaurs like Pachycephalosaurus had sturdy skulls, and knocking heads remains common in bighorn sheep, chameleons and even whales.

But the researchers suggested that Discokeryx was uniquely adept at head-to-head combat. The team scanned and reconstructed Discokeryx’s skull and neck in three dimensions. They then compared it with modern head-butters: muskoxen, argali mountain sheep and Himalayan blue sheep. Using computer models, they deduced that Discokeryx’s skull absorbed more strikes and better cushioned its brain than its modern counterparts. It might have died without that – the team estimated that collisions between Discokeryxes were likely twice as forceful as head-butting muskoxen, which strike each other at nearly 25 mph.

The series of interlocking neck joints have yet to be discovered in any other vertebrate, living or dead, giving Discokeryx the most-optimized head-bashing gear yet discovered, according to the researchers. “This animal is an extreme example of using head-butting as a fighting tool,” Meng said.

While the biomechanics of the new fossil are interesting, that they butted heads is not particularly surprising, said Nikos Solounias, a paleontologist at the New York Institute of Technology who studies giraffe evolution and was not involved in the new study. Virtually all modern hoofed mammals use their heads to tussle, including modern giraffes. But their violent combat style differs from how Discokeryx dueled. Giraffes “hit sideways with their head and neck,” instead of head-on, clobbering each other with their bony, hornlike ossicones, Solounias said.

While it appears that some of the earliest giraffe relatives like Discokeryx were built more for fighting than foraging, they still had a specialized diet. Although they were unable to reach the treetops, chemical analyses of Discokeryx’s teeth revealed that the ancestral giraffe occupied a distinct ecological niche.

Wang believes that ancestral giraffes’ penchant for fighting eventually aided skyward foraging.

“As the males used their necks for fiercer and fiercer fights and their necks became longer and longer, they finally could reach the tallest leaves,” he said.

This article originally appeared in The New York Times.

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