Ancient giraffes evolved for fighting
Anewly identified ancient species may help shed light on a question everyone asks about giraffes – why do they have such long necks?
Remains of Discokeryx xiezhi – a relative of modern giraffes that lived about 17 million years ago, have been found in northern China. Their unusual features have offered new clues to why these planteating mammals developed their unusual shape.
The giraffe’s neck is often used to demonstrate a scientific idea called evolution by natural selection, which explains how species adapt and change over many generations. Individuals with features that make them better suited to their environment than others, are more likely to survive and pass on those features to their babies. In the past, scientists suggested that giraffe ancestors with longer necks benefited by reaching food that was out of reach for other animals, and so all giraffes evolved to have this eyecatching feature.
An alternative theory is that giraffe necks evolved for battle. Today, male giraffes compete for females by swinging their necks and heads at each other, so could necks have grown longer to deliver more powerful blows?
The sheep-sized Discokeryx xiezhi lacked the modern giraffe’s long neck, but had other unusual features; its skull was thick and flattened on top and its neck bones were extremely thick. The Chinese-led team who described these features say they show Discokeryx was built for headbutting rivals, and argue that “courtship combat” (fighting to win a mate) was a big deal for the entire giraffe family. This may be because these ancient species lived in sparse grasslands where food was scarce so the animals had to be super-competitive to survive. Different species found different ways to slug it out, but the scientists say evidence of ancient rivalry supports the idea that “neck combat” was likely to be the reason why giraffes evolved to have long necks.
Once long necks had developed, being able to nibble treetop leaves was a bonus that offered a new source of food. The benefits of reaching higher may still explain the modern giraffe’s long legs.