Evidence of sexual combat between males 400 million years ago

Jan. 17 () –

A unique specimen suggests that male trilobites were already fighting each other with trident-like structures as early as 400 million years ago. to gain the opportunity to mate with females.

A new article, published in Proceedings of the National Academy of Sciencesdescribes how in those ‘jousting’ between arthropods the contestant who knocked over his rival won.

If confirmed, it could be one of the oldest tests of sexual competence and sexual selection ever discovered.

Professor Richard Fortey, a co-author of the study and a Scientific Associate at the Natural History Museum, says it’s a statement: “The extraordinary Devonian trilobite Walliserops wore a unique giant trident on its head, the purpose of which has long been a mystery.”

“We now believe it was used for jousting between males fighting for dominance. The evolution of sexual competition in animals is hundreds of millions of years older than we thought.”

The article also speculates that these trilobites were sexually dimorphic, meaning that males and females looked different. However, the authors note that more evidence will be needed to conclude if this is the case.

Since Walliserops was described in 2001, it has been equally difficult to understand the function of trilobite tridents. Although they have been considered to play a role in sexual selection, it is also possible that they perform other functions of defense, digging or detecting food.

To make the extraordinary claim that tridents play a role in sexual selection, the researchers needed extraordinary evidence. They believe they found them in the collections of the Houston Museum of Natural History.

The trilobite in this study is distinguished from many other museum specimens of Walliserops by its unique trident. Instead of having three points, or barbs, it is the only known specimen with four.. The quills are all of equivalent size and there are no signs of injury, suggesting that he was born with four as a result of a genetic mutation.

Even more important than the four-pronged trident itself is the fact that the specimen has reached adulthood. Upon reaching adulthood, it shows that the characteristic that differentiates it from other trilobites it had no significant impact on their chances of survival.

This suggests that it is unlikely to have played a role in feeding or digging, as the changes that the fourth tooth causes in the general shape of the trident would have made it difficult to use for these purposes, limiting the individual’s chances of survival.

It may also have influenced the probability that the trilobite competed for a mate, but the individual’s mating success, or lack thereof, would not have affected its chances of survival. Deer with abnormal antlers, for example, can survive until they grow up.

Although there are no features of living animals that can be directly compared to the tridents of these trilobites, the striking weapons of rhinoceros beetles are very similar. They have large horns that can reach half the length of their body. and are used in fights between males during the mating season.

The researchers analyzed the shape of Walliserops’ tridents and compared them to beetle weapons to try to understand how they might have been used. They discovered that the shape of the trident was very similar to that of beetles that attempt to overturn their opponents with shovel-like weapons.

When trilobites lived 400 million years ago, it is believed that they used their tridents to poke each other before trying to get under their rival and knock him over. Although flipping trilobites were not necessarily trapped, the time they could take to right themselves would have given the victorious males a chance to mate with the females.

These females may not have trident if trident is a sexually selected characteristic. In this case, the females could have been inadvertently placed in an entirely different species group, but this would be difficult to prove.

If tridents are accepted as examples of sexually selected characters, they will add to a growing body of evidence, such as the recent discovery of male claspers, that at least some trilobite species could be sexually dimorphic.