Fossil trilobites fought for females in "trident fights" 400 million years ago

An international team of paleontologists studied the structure of an invertebrate fossil arthropod

Valliserops.An unusual trident was found on the head of this trilobite. Researchers believe this is the oldest evidence of sexual selection. With the help of these “weapons,” animals fought in “knightly tournaments” about 400 million years ago.

Scientists examined the well-preserveda trilobite fossil held at the Houston Museum of Natural History. It differs from its relatives thanks to a unique trident: it has not three, but four processes. They are all about the same size and there are no signs of damage, suggesting that the animal was born with four teeth as a result of a genetic mutation.

Vallicerops is a mutant with a four-pronged trident. Image: Alan Gishlick, National History Museum

The researchers point out that the fact thatthe mutated vallicerops survived to adulthood, precluding the use of a trident for feeding or digging. In both of these cases, the unusual shape of the trident would have made it difficult to use, limiting the trilobite's chances of survival.

The only possible alternative is believed to beresearchers: the use of this process in sexual competition. They believe that the male valiserops fought over the females, trying to flip their rival with a trident. Trilobites that have fallen on their backs take time to return to their normal position. This gave the victorious males the opportunity to mate with the females.

Artistic illustration of the Wallicerops battle. Image: Alan Gishlick, National History Museum

Sexual selection is an evolutionary processinfluencing characteristics associated with reproduction. It can affect both primary and secondary sexual characteristics: for example, the tail of a male peacock or the branched antlers of a deer. 

Researchers note that although sexualdimorphism (differences) are widespread in many late animals; they were not observed at the first stages of evolution. If the theory of scientists is confirmed, valiserops will become the most ancient species with sexual competition.

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Cover image: Moussa Direct Ltd., CC BY-SA 3.0, via Wikimedia Commons