In grade school, we were told that giraffes had long necks so they could eat the leaves off tall trees. That was speculation, and didn't quite hold up. Other animals in the same parts of Africa ate leaves that were just as nutritious from shorter trees and shrubs, and a giraffe with a very long neck expends a lot of energy just pumping blood that far. An ancient species of giraffe ancestor discovered in China in 1996 might give us a clue. This giraffoid, estimated to be about 16.9 million years old, resembles a giraffe but with a much shorter neck. It was named Discokeryx xiezhi.
What intrigued scientists was the thickness of the fossil's skull. It had layers of keratin on top that totaled around five centimeters thick. This would have been perfect for head-butting each other. Fighting with one's head as a weapon is still seen in giraffes today. The skull-fighting may have led to an elongated neck over time, as giraffes with slightly longer necks outperformed those with shorter necks in the competition for mates, therefore passing on those long-neck genes. Read more about Discokeryx xiezhi and what it tells us at Nature.
(Image credit: Y. Wang and X. Guo)
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