An illustration of Anomalocaris.© Katrina Kenny
First discovered in the late 1800s, Anomalocaris canadensis—which means “weird shrimp from Canada” in Latin—has long been thought to be responsible for some of the scarred and crushed trilobite exoskeletons paleontologists have found in the fossil record.
“That didn’t sit right with me, because trilobites have a very strong exoskeleton, which they essentially make out of rock, while this animal would have mostly been soft and squishy,” said Russell Bicknell, a postdoctoral researcher in the Museum’s Division of Paleontology and lead author of a paper published this week in the journal Proceedings of the Royal Society B that bears out his suspicion.
Recent research on the armor-plated, ring-shaped mouthparts of A. canadensis had raised doubts about the extinct marine animal’s ability to process hard food. Bicknell, who conducted the work while at the University of New England in Australia, and a team that included scientists from Germany, China, Switzerland, the United Kingdom, and Australia set out to investigate whether the predator’s long, spiny arachnid-like front “legs” could do the job instead.
The first step was to build a 3D reconstruction of A. canadensis from extraordinarily well-preserved—but flattened—fossils of the animal found in Canada’s 508-million-year-old Burgess Shale. Using modern whip scorpions and whip spiders as analogues, the team showed that the predator’s segmented appendages were able to grab prey and could both stretch out and flex. But a modeling technique called finite element analysis, showing the stress and strain points on this grasping behavior, illustrated that its appendages would have been damaged while grabbing hard prey like trilobites. The 2-foot (60-centimeter) predator, one of the largest animals to live during the Cambrian, was weaker than assumed.
The researchers also used computational fluid dynamics to place the 3D model in a virtual river to predict what body position it would likely use while swimming. They found the animal was likely a speedy swimmer, zooming around with its front appendages outstretched.
The combination of these biomechanical modeling techniques—used together in a scientific paper for the first time—paint a different picture of A. canadensis than was previously assumed. It was probably agile and fast, darting after soft prey in the open water rather than pursuing hard-shelled creatures on the ocean floor.
“Previous conceptions were that these animals would have seen the Burgess Shale fauna as a smorgasbord, going after anything they wanted to, but we’re finding that the dynamics of the Cambrian food webs were likely much more complex than we once thought,” Bicknell said.