One 400 million-year-old trilobite specimen has revealed new insights into the evolution of sexual combat weaponry. The trilobite’s trident, typically a three-pronged fork that was thought to be used for feeding, had four prongs, leading researchers to believe that it evolved for fighting, not feeding.
“The extraordinary Devonian trilobite Walliserops carried a unique, giant trident on its head, the purpose of which has long been a mystery,” said Prof Richard Fortey FRS, Scientific Associate at the Natural History Museum London and co-author of a new paper in a statement sent to IFLScience. “We now believe that it was used for ‘jousting’ between males striving for dominance.”
The trilobite fossil is a Walliserops trifurcatus specimen that had grown to full maturity and adult size before it died and became a part of the fossil record. It had a malformed trident equipped with four tines instead of three, but despite this was able to survive to adulthood.
If the trident was a crucial tool for feeding, having a malformation would be expected to lead to early death as the animal couldn’t feed properly. Since this trilobite clearly got by just fine with its unique trident, researchers in the new paper hypothesized that it might instead have been used in sexual combat.
Anatomical weaponry for fighting over potential mates is widespread across the animal kingdom, but perhaps the most comparable in the case of trident-wielding trilobites are rhinoceros beetles from the subfamily Dynastinae. As their name suggests, these arthropods have horn-like protrusions on their heads which they use for jousting competing males in an effort to score a mate.
The position and inflexibility of the Walliserops trident also seemed an unlikely fit for feeding apparatus, but a comparison of its trident against the secondary sexual features of comparable living species within Dynastinae revealed similarities. It seems the tridents of Walliserops trilobites would’ve been in just the right place for fighting over females, which could explain how our malformed four-tined-trident specimen was able to thrive despite having a less conventional bit of kit on its head.
With the morphometric analysis supporting the hypothesis that the trilobite’s trident was used in sexual combat, Walliserops becomes the oldest known example of sexual combat weaponry known to science.
“The evolution of sexually motivated competition in animals is hundreds of millions of years older than we thought,” concluded Fortey.
The study was published in the journal PNAS.