Fossils of Ancient Giraffe Shows Competition for Mates Could Be the Reason for Their Long Necks

In the vast, dry expanse of northern China's Junggar Basin lies fossils of a beast that shed light on the evolution of the giraffe family, Scientific American reported. In 1996, paleontologist Jin Meng uncovered a strange skull that was robust and heavily built with a bony plate that was almost one inch thick near the animal's forehead. Meng also discovered a few neck vertebrae that were conspicuously thickened, which implies it was able to withstand strong force when alive.

For years it remained unnamed and was simply called guài shòu, or "strange beast." But now they finally gave it an official name: Discokeryx xiezhi. The beast is believed to have lived some 16.9 million years ago and was an early relative of today's giraffes. But unlike modern giraffes, its skull and vertebrae were different and were believed to be the result of sexual competition.

Giraffe Relative Use Headbutting to Compete for Mates

Charles Darwin assumed in his theory that natural selection driven by food has given giraffes their long necks to reach higher trees and have their private food supply and away from the competition.

Meng said that people usually associate giraffes with their long necks, but the analysis of fossils of a giraffe relative suggests there might be more to that story. It shows that even phylogenetically related animals could evolve in different directions.

More than 25 years ago, paleontologists unearthed an unusual fossil in a 15-million-year-old rock formation in China. According to an article in Science, its skull was thickened at the base and was still connected to an enlarged neck vertebra. Years later, scientists used CT scans to analyze the skull and found that the inner ear bones were of a giraffoid, one of the early ancestors of modern giraffes.

The team tried to reconstruct the bones through the information from the CT scans and found that these animals had a hand-size bony disk with a horny helmet at the top of their head. Computer simulations then revealed how it formed its head and neck, given the strong impacts it might have experienced.

They compared their data with other giraffoids and animals, such as sheep and musk ox, who also headbutt or lock horns to compete for mates. Although the bones were not as thick as those of other animals, they had a surface area in contact with the base of the skull, which is unusual.

Simulations reveal that modifications keep their necks from snapping and that the horny helmet was a powerful buttress for jousting with competitors.

How Did the Giraffe Relative Look Like?

During the mid-Miocene period, Northern China's contemporary desert was warm, wet, and suitable for a diverse suite of species to live in, Scientific American reported. Meng and colleagues tried to piece together D. xiezhi's story using a variety of clues, which included analyzing enamel from a tooth they recovered while performing the CT scans of two skulls.

They compared it with 50 other species found in the same area and found evidence pointing to D. xiezhi sharing some morphological characteristics with modern giraffes, perhaps even feeding on a mix of leaves and grass.

Meng said that the animal was not that large, perhaps just as big as a sheep, but its head and neck were probably one of the strongest ever possessed by a mammal. They noted that it has the most complicated head-neck joints in mammals ever found to date.

They describe in full the fossils in the study titled "Sexual Selection Promotes Giraffoid Head-Neck Evolution and Ecological Adaptation," published in the journal Science.

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