One of the Planet's First Predators Was a Lot Dumber Than Its Prey

Paleontologists rarely get insights into the brains of Cambrian animals, but every now and then, the Earth delivers up a winning specimen. Such is the case with an extraordinarily well-preserved fossil of the new species Lyrarapax unguispinus, a name that translates to something like “lyre-shaped predator with thorny claws.”

The animal lived about 520 million years ago, and was among the very first hunters to swim the Cambrian seas. Its brain was fossilized in exceptional detail, along with its digestive tract and muscles, providing researchers with a rare glimpse into the mind of one of our planet’s very first carnivores. An international team of neuropaleontologists—master decoders of prehistoric brains—published their analysis of the specimen today in Nature.

One of their most interesting findings was that there wasn’t a whole lot going on upstairs with this apex predator. Even compared to the primitive animals it likely preyed on, Lyrarapax’s was simple-minded. “It turns out the top predator of the Cambrian had a brain that was much less complex than that of some of its possible prey and that looked surprisingly similar to a modern group of rather modest worm-like animals,” said senior author Nicholas Strausfeld of the University of Arizona in a statement.

But what Lyrarapax lacked in brains, it made up for with its spiked appendages, which framed the predator's head. These twin face-scimitars were the defining feature of the Lyrarapax’s larger family—the anomalocaridids, or “abnormal shrimp.”

Abnormal is an understatement. "Anomalocaridids are the biggest animal in the Cambrian ocean; some specimens can reach two metres in length," co-author Xiaoya Ma told me over email. "All had swimming flaps, one pair of spiny grasping legs and huge compound eyes, and all these features make them highly efficient hunters."

Not only did the family sport those nightmarish cranial graspers, but they also shared freaky rounded mouths shaped like pineapple rings. The teeth jutted out towards the center but never met (shudder). On top of that, their dorsal regions were protected by segmented blades that may have doubled as gills.

Because of the family’s bizarre bundle of traits, paleontologists have long debated the place of the anomalocaridids in the tree of life. The new Lyrarapax specimen has shed new light on the ongoing debate, and the team's findings strongly suggest that today’s onychophorans (or velvet worms) are the closest living relatives of this ancient family.

"Anomalocaridids share a set of characteristics with onychophorans or arthropods, or with both," said Ma. "They also possess some unique features only seen in this group. In this research, the brain and neuroanatomical features shared by anomalcoaridids and onychophoran represent an ancestral condition towards arthropod evolution."

It would seem the apple doesn’t fall far from the tree in terms of weird adaptations—velvet worms hunt by squirting slime at their prey, for example. And like their Cambrian relatives, velvet worms are also much more simple minded than their prey.

"Onychophorans today are also exclusively predators, and they prey on beetles and other small insects which have more complex brains," Ma told me.

But again, who needs brains when you have slime-shooters? When it comes to both anomalocaridids and onychophorans, the winning strategy is usually the weirdest.