Meet the Arthropod That Originated Fangs
Evolutionary biologist Rudy Lerosey-Aubril was meticulously cleaning a small, 500-million-year-old arthropod fossil with a needle when he noticed something strange: There were claws where its antennae should be.
“The claws are never in this location in a Cambrian arthropod,” Lerosey-Aubril explained in a statement. “It took me a few minutes to realize the obvious, I had just exposed the oldest chelicera ever found.”
Unearthed in the Western Utah Desert, this three-inch specimen was the first known member of the arthropod subphylum chelicerata, a group that includes spiders, mites, horseshoe crabs, scorpions, and more. While other arthropods, such as insects, have antennae as their main appendages, chelicerae have specialized mouthparts called “chelicerae” that are typically used for feeding. The chelicerae of spiders, for example, evolved into venomous fangs.
Double Megachelicerax cousteaui according to the famous oceanographer Jacques Cousteau, Lerosey-Aubril described the species in an article published in Nature. This discovery pushes back the origins of the chelicerate lineage by 20 million years, to a time when evolution was tinkering with a number of new models: the Cambrian explosion. It also represents a sort of missing link in arthropod evolution, connecting arthropods lacking specialized mouthparts to primordial horseshoe crab-like chelicerae.
Read more: “In search of the first animals”
“This tells us that by the mid-Cambrian, when evolutionary rates were remarkably high, the oceans were already inhabited by arthropods whose anatomical complexity rivaled modern forms,” added Javier Ortega-Hernández, co-author of the study.
Such new anatomical complexity did not immediately translate into ecological dominance, the researchers said. Instead, it appears that the tiny predators languished for several millennia while more primitive arthropods like trilobites predominated in ancient oceans.
“A similar evolutionary pattern has been documented in other animal groups,” Lerosey-Aubril said. “This shows that evolutionary success is not just a matter of biological innovation: timing and environmental context are important.”
Over the next hundreds of millions of years, the descendants of M. cousteaui diversified to colonize land, leaving more than 120,000 living species scattered in various ecological niches. Quite a legacy for a three-inch upstart from the primordial seas.
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Main image: artistic reconstruction by Masato Hattori (© Harvard University).
