Beast built for head-butting reveals early giraffe neck evolution

Fossils unearthed in China of a forerunner of the modern giraffe are offering insight into the early evolution of this mammal's trademark long neck, driven not only by the benefit of reaching high foliage but also by head-bashing competition between males for mates.

Researchers on Thursday described skeletal remainsincluding a thick skull and strong neck bones of an early member of the giraffefamily called Discokeryx xiezhi, roughly the size of a large bighorn sheep,that lived about 17 million years ago in the Xinjiang region in northwesternChina.

Discokeryx's solidly built skull and strong cervicalvertebrae were well adapted to high-speed head-to-head impact like that seen incompetition among males of some mammal species for female mates, according tothe researchers. Discokeryx boasted, they said, the most complex joints betweenthe head and neck as well as between the individual neck bones of any mammal.

Discokeryx's skull was topped by a single largedisc-shaped and helmet-like ossicone, the name for the horn-like knobs atopgiraffe's heads.

"Ossicones, like horns and antlers, usually serveas weapons for males fighting for mates," said Chinese Academy of Sciencespaleontologist Shi-Qi Wang, lead author of the study published in the journalScience.

Discokeryx means "disc-horn," while xiezhirefers to a single-horned beast in Chinese legend.

"Discokeryx has extreme morphologies of the headand neck adapted for head-butting behavior," said paleontologist and studyco-author Jin Meng of the American Museum of Natural History in New York.

"The traditional hypothesis for driving theelongation of the giraffe neck is eating - reaching up to get tree leaves. Thisnew finding shows that, in the giraffe family, members do different things intheir early evolution. The new species represents an extreme example in whichthe neck is not elongated but becomes very thick to absorb the power and impactfrom powerful head-butting," Meng added.

Another hypothesis for giraffe neck evolution - onesupported by Discokeryx's anatomy - is that elongation was driven by behaviourdisplayed in competition for mates like the "necking" seen ingiraffes today in which males violently strike each other with their necks.Longer-necked males often win these duels.

"If a male giraffe has a shorter neck, then thefemale may refuse the mating request of the male," Wang said.

Neck elongation independently evolved among severalanimal groups dating back hundreds of millions of years, also including marinereptiles such as Elasmosaurus and Tanystropheus, the various sauropod dinosaursincluding Patagotitan and Mamenchisaurus and even swans and geese living today.

Discokeryx, according to the researchers, may offer apeek at the early stages of giraffe neck elongation that unfolded over millionsof years, though this species took a different evolutionary route specialisedfor head-butting. Discokeryx is not considered a direct ancestor of today'sgiraffe, but rather a side branch of the giraffe family.

The modern giraffe, found in sub-Saharan Africa, isthe world's tallest living land animal, with males up to 18 feet (5.5 meters)tall and females up to 14 feet (4.3 meters) tall. A giraffe's neck, stretchingabout six feet (1.8 meters), is the longest of any extant animal, though it hasjust seven neck bones like other mammals.

Discokeryx inhabited an open grassland with patches oftrees and shrubs during a time known as the Miocene epoch. It lived alongsideshovel-tusked elephants, hornless rhinos, horned pigs, deer with crown-likeantlers, three-toed horses and various antelopes. Predators includedsaber-toothed cats, hyenas and a member of a mammalian group called "dogbears" as big as a polar bear.

"Discokeryx most likely ate grasses," Mengsaid.