This ‘Jousting’ Trilobite Might Be the First Known Creature to Fight for a Mate

Using a “trident” attached to its head, the arthropod may have competed for sexual dominance 400 million years ago

a trilobite fossil with a long, three-pronged trident coming out of its head
Extinct trilobites called Walliserops trifurcatus may have been among the first creatures on Earth to engage in sexual combat, a new study finds. Public Domain

At the bottom of the ocean 400 million years ago, a knight in shining armor may have used a long trident to joust against the competition and win the hand of a fair lady.

That so-called knight was, in reality, a trilobite called Walliserops trifurcatus—and it may provide one of the oldest known examples of sexual combat in the fossil record, according to a study published Tuesday in Proceedings of the National Academy of Sciences.

This extinct arthropod had a giant trident protruding from its head. But for a long time, the purpose of this curious head ornament remained a mystery.

Previously, scientists hypothesized the trilobites might have used it to defend against predators, burrow in the mud or sense food. However, the researchers say the trident’s stiffness, angle and length make it too immobile for defense and too awkward for foraging.

“We now believe that it was used for jousting between males striving for dominance,” says paleontologist and study co-author Richard Fortey in a statement. “The evolution of sexually motivated competition in animals is hundreds of millions of years older than we thought.”

To support this, the authors cite a fully grown specimen of Walliserops with a mutation causing it to have four, rather than three, prongs on its trident. Since the trilobite was able to grow to maturity without being impacted by the different shape of its trident, the researchers say the trident was likely a sexual structure, rather than one used for feeding or digging.

“When we see something like the fork on Walliserops, it suggests sexual selection because it’s really extreme,” Alan Gishlick, a paleontologist at Bloomsburg University of Pennsylvania and an author of the study, says to the New York Times’ Asher Elbein. “It’s just a question of how you test it.”

When it comes to fossils, it can be difficult to figure out the functions of any strange anatomical structures. It’s much easier to learn that deer antlers are made for dueling when you can observe as bucks battle it out for territory. When the subject is extinct, however, things get a bit trickier.

One way to solve the mystery is by attempting to find a living species with a comparable structure. However, as Popular Science’s Laura Baisas writes, “when structures are found in fossils, comparisons can be problematic, since it’s not always clear what feature on a living species can be used to compare.”

In the case of the trilobite’s trident, researchers couldn’t find a direct comparison, but they did draw a broad parallel to the shape of a rhinoceros beetle’s horn. They analyzed the shape of the tridents, determining they were most similar to beetles that use their horns as shovel-like weapons to tip their combatant over.

Still, Robert J. Knell, a paleontologist at Hull University in England who did not participate in the study, tells the Times that he’s not yet sold on the study’s argument, pointing out that weapons for sexual combat usually show up on males of a species. The researchers assumed the trident-toting trilobites were males, but no Walliserops females have been conclusively identified. “I’m not convinced that there’s a smoking gun there,” Knell says to the publication. “But I think they’ve done a good job in excluding other explanations.”

In addition to sexual combat, researchers have also found that trilobites displayed some of the earliest evidence of group behavior. Jean Vannier, an expert on evolution and the geosphere at the University of Lyon, France, who was not involved in the study, tells Riley Black of New Scientist, “it is amazing to see that such complex behaviors appeared very early in the course of evolution and have endured to the present day.”

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