Image: Reuters Berita 24 English - Fossils of a predecessor of the contemporary giraffe discovered in China are providing insight into the...
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| Image: Reuters |
Berita 24 English - Fossils of a predecessor of the contemporary giraffe discovered in China are providing insight into the early evolution of the mammal's signature long neck, which was driven not only by the benefit of reaching high vegetation but also by male-to-male head-bashing competition for mates.
Researchers described skeletal remains of an early member of the giraffe family called Discokeryx xiezhi, roughly the size of a huge bighorn sheep, that lived around 17 million years ago in the Xinjiang region of northern China, with a massive cranium and powerful neck bones.
According to the researchers, Discokeryx's firmly formed skull and powerful cervical vertebrae were well adapted to high-speed head-to-head impact, such as that seen in competition between males of some mammal species for female females. They claimed that Discokeryx has the most complicated joints of any animal, both between the head and neck and between the various neck bones.
A single huge disc-shaped and helmet-like ossicone, the word for the horn-like knobs atop giraffe heads, crowned Discokeryx's skull.
"Ossicones, like as horns and antlers, are generally used as weapons by males battling for mates," said Shi-Qi Wang, a paleontologist at the Chinese Academy of Sciences and main author of the study published in Science http://www.science.org/doi/10.1126/science.abl8316.
Discokeryx means "disc-horn," whereas xiezhi is a Chinese fable about a single-horned beast.
"Discokeryx exhibits extreme morphologies of the head and neck adapted for head-butting behavior," said Jin Meng of the American Museum of Natural History in New York, a paleontologist and research co-author.
"Eating - reaching up to gather tree leaves - is the traditional explanation for the giraffe neck's elongation. This new discovery demonstrates that members of the giraffe family accomplish distinct things in their early evolution. The new species is an extreme case in which the neck is not stretched but becomes extremely thick in order to withstand the force and impact of strong head-butting "Meng went on to say.
Another theory for giraffe neck evolution, supported by Discokeryx's anatomy, is that elongation was driven by behavior found in giraffes today, such as "necking," in which males fiercely hit each other with their necks in competition for mates. Males with longer necks are more likely to win these fights.
"If a male giraffe's neck is shorter, the female may deny the male's mating request," Wang explained.
Neck elongation evolved independently in a number of animal groups over hundreds of millions of years, including marine reptiles like Elasmosaurus and Tanystropheus, sauropod dinosaurs like Patagotitan and Mamenchisaurus, and even modern swans and geese.
According to the researchers, Discokeryx may provide a glimpse into the early phases of giraffe neck extension, which occurred over millions of years, however this species evolved in a different way, specialized for head-butting. Discokeryx is a side branch of the giraffe family, rather than a direct ancestor of today's giraffe.
The contemporary giraffe is the world's tallest living land animal, standing up to 18 feet (5.5 meters) for males and 14 feet (4.3 meters) for females in Sub-Saharan Africa. A giraffe's neck is the longest of any extant animal, reaching roughly six feet (1.8 meters), yet having only seven neck bones like other mammals.
During the Miocene epoch, Discokeryx lived in an open grassland with pockets of trees and bushes. It coexisted with elephants with shovel-tusks, rhinos without horns, pigs with horns, deer with crown-like antlers, three-toed horses, and numerous antelopes. Predators included saber-toothed cats, hyenas, and a polar bear-sized member of the mammalian species known as "dog bears."
"It's very likely that Diskokeryx ate grasses," Meng remarked.
