Mystery of the world's largest antlers

A new study of deer antlers has proved that nothing is straightforward in understanding animal evolution!

For decades scientists trusted in the principles of allometry, a scaling relationship between the size of a body part and the overall size of the animal. About 50 years ago, influential biologist Stephen Jay Gould suggested the Irish Elk’s enormous antlers – up to 3.5m from tip to tip, were related to shoulder height – the taller the animal, the wider the antlers.

Now Dr Mark Grabowski, senior lecturer in evolutionary anthropology, working with Norwegian biologist Thomas Hansen, says the sums don’t add up and points to diet, habitat and competition from rival elks as factors in the size of the extinct animal’s weapons.

Mark and colleagues found data and methods used by Gould were “really poor by standards of today”. For instance, some of Gould’s figures on deer shoulder height were based on estimates given in a book about big-game hunting, while they also contest antler length as a measure of their size, saying antler volume is a more accurate measure.

Grabowski and Hansen’s own analyses found allometry predicted the Irish Elk should have an average antler volume of 17.5 litres. In reality, the ancient deer’s antlers were boasted an average volume of 25.5 litres!

The result came as a surprise, Hansen told New Scientist. “I would have loved to be able to confirm and strengthen Gould’s analysis,” he says. “But it’s not quite how it turned out.”

Mark says Gould wasn’t entirely wrong and allometry still plays an important role, but the new results indicate that additional factors drove the evolution of the Irish Elk’s enormous antlers.

Unfortunately, it is challenging to definitively identify those factors because species has been extinct for about 7700 years, which means we can only study their skeletons – many of which have been discovered in Irish peat bogs. For instance, males with big antlers probably benefitted during the breeding season, but we don’t know how because we can’t study the Irish elk’s behaviour.

“In some species, it’s important for males to have big antlers to fight and intimidate other males,” says Hansen. “In other species, large antlers are more important for displaying to attract females.”

Nutritious diets could have been important too, the researchers say, to help males find the energy to grow their antlers every year – and habitat probably played a part, with males presumably living on open landscapes so that they didn’t continually tangle their antlers among tree branches.

Image: Illustration of an Irish Elk. Daniel Eskridge.