this “trident” may be the oldest known sexual weapon

A new paper claims that a strange trident-shaped anatomical feature formed in the mouth of a trilobite 400 million years ago may be the earliest known example of a specialized sexual weapon in the kingdom.

Trilobites are ancient creatures that look like giant, helmeted bugs. These armored invertebrates thrived in the oceans for 270 million years before finally becoming extinct during the Great Extinction at the end of the Permian period, about 252 million years ago.

Trilobite species once numbered in the thousands. One of them, Walliserops trifurcatus, differed from the others in terms of its characteristics a large trident-shaped appendage with a flat blade sticking out of his face. In a study published last Monday in the journal Proceedings of the National Academy of Sciences, two researchers from Bloomsburg University (Pennsylvania) propose the idea that this trident was used. a weapon to fight rival men.

3D visualization of W. trifurcatus and its trident. Credit: Alan D. Gishlick

Sexual choice

Characteristics sometimes evolve through sexual selection to become ornaments or weaponry, thus giving their possessor a physical advantage in the context of potential mating. Peacock feathers are a fine example of ornamentation, while deer antlers are examples of weapons that allow males to fight for females.

Methods of sexual struggle probably appeared very soon after the evolution of the first forms of complex life. However, identifying sexually selected traits in extinct animals is a difficult task, in part because their social behavior cannot be observed. Things get even more complicated when these organisms evolved hundreds of millions of years ago.

These limitations have led some researchers to err on the side of caution and seek other practical explanations for these anatomical differences. After it was discovered in Morocco in 2001 and described, some researchers believed that Walliserops’ famous “trident” defensive weaponwhen others imagine it a a tool for obtaining food.

In this new work, scientists refute both of these ideas for several reasons. On the one hand, this long and rigid trident was not mobile enough to allow effective defense. It was too long and oddly angled to get food. Incidentally, a deformed trident can be seen in one of the mature specimens on display at the Houston Museum of Natural Science. However, we know that wild animals have serious deformations in their feeding or defense mechanisms usually does not survive to adulthood. However, defective sexual selection structures do not actually prevent survival. They simply prevent mating.

Still an open question

Scientists measured the tridents of different specimens and compared them to rhinoceros beetles, known for their horns, which the males use to fight each other. According to these analyses, Walliserops’ weapon most closely resembled his own Japanese rhinoceros beetle (Allomyrina dichotoma) uses a rake-like cephalic horn to hand over rival suitors.

trident trilobite
A morphometric comparison of the trilobite’s trident revealed similarities with the sexual combat arms of some insect species. Credit: Alan D. Gishlick

Note that the results of this study are interpretations only. The true role of these horns is still debated, as several points remain to be clarified. For example, such sexually selected weapons are found only in men. No female Walliserops has ever been definitively identified, but sexual differences are difficult to discern in the fossil record. On the other hand, sexual weapons also tend to grow significantly according to the animal’s body size. However, it is still difficult to make such observations on fossils that are more than 400 million years old.

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