There is a weird quirk in the sex ratio of woolly mammoth remains dug out of the frigid earth of icy Siberia. In general, far more male mammoths are pulled from the ground than females, and now a study published in Current Biology has speculated as to why. It's possible that the males were simply more reckless and likely to get caught in natural traps than females, who were part of a herd.

The study came about as a bit of an accident, really. As part of a larger project, the researchers were looking into the genomes of the woolly beasts, and as such needed to know the sex of a small number of mammoths. But as they were going along, they noticed that they were consistently sexing more males than females.

“We were very surprised because there was no reason to expect a sex bias in the fossil record,” explains first author Patrícia Pecnerova in a statement. “Since the ratio of females to males was likely balanced at birth, we had to consider explanations that involved better preservation of male remains.”

The researchers then decided to expand the sexing of individuals, and encompassed mammoth populations from across both Siberia and Wrangel Island. Once again, they found that there were more males in the fossil record than females – seven out of every 10 mammoths studied were male. 

The fossilized remains of any animal is extremely rare, and the researchers think that many of the mammoths were likely preserved after they fell into natural “traps”, such as bogs and lakes, and were thus covered rapidly after death. This, they suspect, is the explanation as to why more males are now found.

They argue that the results back up the notion that woolly mammoths lived in social structures much like modern-day African elephants do, in which the females stay in their natal group and the males wander out on their own until they come together in bachelor herds. As the males have to go it alone, they are more likely to take risks and get into sticky situations, which in turn means that they are more likely to die in conditions favorable for their preservation.

The females, on the other hand, have the benefit of being in a herd led by an experienced older female, or matriarch. These bigger, older females would have a wealth of knowledge about the local environment, such as which parts of the landscape to avoid and when.

The work shows how fossils can provide an insight into the social structure of animals, but also serves as a reminder that fossils don't always represent a random sample of populations.