The Miocene giraffe had a disc-shaped headgear and head-neck joints suitable for combat against headbutts

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Paleontologists have identified a new species of giraffoid that lived in northern China during the early Miocene about 17 million years ago. Appointed Discokeryx xiezhi, the ancient creature had a thick-boned skull with a large disc-shaped headgear, a series of cervical vertebrae with extremely thickened centra, and the most complicated head-neck joints known to date in mammals. This particular morphology was most likely adapted for fierce head-butting behavior between males, comparable to neck-butting in male giraffes. Researchers argue that selection for such a fight also played a role in forming the group’s long necks.

Male fight in Discokeryx xiezhi. Image credit: Xiaocong Guo.

The characteristic long neck of the modern giraffe – the tallest land animal and largest ruminant on the planet – has long been considered a classic example of adaptive evolution and natural selection since Charles Darwin first wrote the concepts for it. time.

It is commonly believed that competition for food resulted in elongated necks and allowed giraffes to browse treetop leaves in African savannah forests that were well beyond the reach of other ruminant species.

However, others have supported a neck-for-sex hypothesis, suggesting that sexual selection driven by inter-male competition may also have contributed to the evolution of the neck.

“Fossils of ancient giraffe species can help clarify these evolutionary mechanisms,” said Dr Shi-Qi Wang of the Chinese Academy of Sciences’ Institute of Vertebrate Paleontology and Paleoanthropology and colleagues from China, from the United States, Germany, Switzerland and Austria. .

The fossil community of the Junggar Basin, China, 17 million years ago.  Image credit: Xiaocong Guo.

The fossil community of the Junggar Basin, China, 17 million years ago. Image credit: Xiaocong Guo.

The newly identified giraffoid species, Discokeryx xiezhihad a helmet-like headgear and particularly intricate head and neck joints indicative of intense head-butting combat.

“The living giraffes and Discokeryx xiezhi belong to the superfamily Giraffoidea,” Dr. Wang said.

“Although their skull and neck morphologies differ considerably, both are associated with male courtship struggles and both have evolved in an extreme direction.”

Discokeryx xiezhi had many features unique among mammals, including the development of a large disc-shaped ossicone in the middle of its head,” said Professor Tao Deng, a researcher at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, CAS Center. for Excellence in Life and Paleoenvironment, and the College of Earth and Planetary Sciences at the University of the Chinese Academy of Sciences.

In addition, data on tooth enamel isotopes Discokeryx xiezhi suggest that the species also likely filled a specific ecological niche in the ecosystem inaccessible to other contemporary herbivores.

“Stable isotopes of tooth enamel indicate that Discokeryx xiezhi lived in open grasslands and may have migrated seasonally,” said Dr. Jin Meng, a researcher at the American Museum of Natural History.

“For the animals of the time, the grassland environment was more sterile and less comfortable than the forest environment.”

“The violent fighting behavior of Discokeryx xiezhi may have been related to survival stress caused by the environment.

According to the authors, the early evolution of giraffes is more complex than previously known, where, in addition to competition for food, sexual combat probably played an important role in the formation of the long and adapted necks of unique way of the group.

Their article appears in the newspaper Science.

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Shi Qi Wang et al. 2022. Sexual selection promotes giraffoid head and neck evolution and ecological adaptation. Science 376 (6597); doi:10.1126/science.abl8316

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