500 million-year-old ‘abnormal shrimp’ used facial spikes to ‘pincushion’ soft prey

About 500 million years ago, a predator no more than a domestic cat swarmed the oceans, searching for prey it could cut through with its spiky facial appendages.

For a long time, paleontologists believed they believed that the arthropod Anomalocaris canadensis, which roughly translates to “the abnormal shrimp from Canada,” employed its spears to break through trilobites as well as other prey with hard shells. But a new study suggests that this Cambrian animal probably hunted soft-bodied animals instead, an article published this week in the Journal Proceedings of the Royal Society B.

“There had been a long-standing question about what was causing the injuries we were seeing on Cambrian trilobites [in the fossil record of Canada’s well-preserved Burgess Shale],” the lead researcher Russell Bicknell, an assistant professor with the American Museum of Natural History in New York City, told Live Science. “It had been hypothesized that A. canadensis was possibly one of the animals that was causing the damage by using its spiky appendages to grab and pierce its prey.”

A shrimp-like A. canadensis grew to lengths of around 3 inches (1 meter) that included two terrifying facial appendages. A different group of researchers had previously suggested that hard trilobites were not part of the apex prey’s food chain based on bite force simulation models. However, the new group’s team took an entirely different approach to the issue.

The researchers constructed three-dimensional computer models of the A. canadensisbased on fossil evidence. They also examined species that could serve as modern-day counterparts to the Cambrian animal, including whip spiders (part of the arachnid family Amblypygi) and whip scorpions ( Uropygi). They examined how modern arthropods use their appendages to capture the prey and keep it in place.

The team concluded that even though it is possible that. Canadensis may have been skilled in taking animals in its grasp; the animal’s two facial appendages would have been too fragile to penetrate the tough exoskeletons of trilobites, which Bicknell stated could likely have “possibly been made up of a similar chemical composition as the cuticle of a horseshoe crab’s exoskeleton.”

“We showed that the spikes on the appendages probably would’ve been damaged if it were to try to deal with harder prey,” Bicknell stated.

The researchers concluded that this hunter from the past targeted soft-bodied animals swimming and floating at the bottom of the ocean.

“This animal probably swam like cuttlefish, with its appendages outstretched in front of it and its flaps undulating to help it accelerate through the water,” Bicknell stated. “It would then grab its prey and puncture it as if it were a pincushion.”


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