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CNN’s Wonder Theory science newsletter offers a fascinating exploration of the universe. Last week, a team of researchers announced the earliest known evidence of sexual combat in the form of a trident-headed trilobite that scuttled the seafloor 400 million years ago. Trilobites were one of the earliest arthropods, and Walliserops was one of the species that stood out due to its trident-shaped protrusion.
Researchers proposed various uses for these forking protrusions, including defense, hunting, and attracting mates. In a paper published in the scientific journal Proceedings of the National Academy of Sciences, researchers Alan Gishlick and Richard Fortey delved into these hypotheses, ruling out the trident as a means of defense or a hunting tool. They concluded that Walliserops used the trident to fight among each other.
To back up their conclusion, the researchers used a technique called landmark-based geometric morphometrics to analyze the surface-level similarity of trilobite tridents and horns of rhinoceros beetles. They found that the trilobite tridents’ shape had a lot in common with the horns of beetles that flip their dueling partners in a “shoveling” motion. Gishlick and Fortey believe that, like in beetles, trilobites’ tridents were “sexual weapons” used by males sparring to win mates.
This could also be the earliest known evidence of sexual dimorphism, as one sex usually does the competition. Growing features such as big combat-ready horns requires a lot of energy, and female animals already have to expend lots of it to produce eggs. However, scientists have no definitive means of telling which Walliserops are male and which are female, and no trident-less Walliserops have been discovered.
Erin McCullough, an assistant professor of biology at Clark University in Massachusetts, agrees with the researchers’ conclusion that the trilobite tridents were likely used for interspecies combat. However, she’s not sold on their argument that this was a trait only possessed by males. She believes that it would have been a stronger story if they had evidence that the females don’t have weapons.
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