Anomalocaris canadensis, a 2-foot (60 centimeter) marine animal, was probably much weaker than previously thought, according to biomechanical studies of the arachnid-like front “legs” of the extinct apex predator. It was probably agile and quick, darting after soft prey in open water rather than hard-shelled creatures on the ocean floor, making it one of the largest animals of the Cambrian. The research was published in the journal Proceedings of the Royal Society. B.
Anomalocaris canadensis, which means “weird shrimp from Canada” in Latin, was first discovered in the late 1800s. It has long been thought to be responsible for some of the trilobite exoskeletons that paleontologists have found in the fossil record that have been crushed and scarred.
“That didn’t agree with me, since trilobites have an exceptionally impressive exoskeleton, which they basically make from rock, while this creature would have generally been delicate and soft,” said lead creator Russell Bicknell, a postdoctoral scientist in the American Historical Center of Normal History’s Division of Fossil Science, who led the work while at the College of New Britain in Australia.
The ability of A. canadensis to process hard food is questioned by recent research on the animal’s armor-plated, ring-shaped mouthparts. The purpose of the most recent study was to determine whether the predator’s long, spiny front appendages might be more effective.
A close-up of the most flexible frontal appendage on a complete specimen of Anomalocaris canadensis from the Cambrian Burgess Shale of Canada. Credit: Alison Daley.
Building a 3D reconstruction of A. canadensis from the exceptionally well-preserved but flattened animal fossils found in Canada’s 508 million-year-old Burgess Shale was the first step for the research team, which included scientists from Germany, China, Switzerland, the United Kingdom, and Australia. The team was able to demonstrate that the predator’s segmented appendages were capable of grabbing prey and could both stretch out and flex by using modern whip scorpions and whip spiders as analogs.
The stress and strain points on A. canadensis’ grasping behavior were depicted using the modeling technique known as finite element analysis, demonstrating that the animal’s appendages would have been damaged while grabbing hard prey like trilobites. The specialists utilized computational liquid elements to put the 3D model of the hunter in a virtual current to foresee what body position it would probably use while swimming.
A pair of appendages from Anomalocaris canadensis. Credit: Alison Daley
These biomechanical modeling methods are used together for the first time in a scientific paper to paint a different picture of A. canadensis than was previously thought. With its front legs outstretched, the animal probably moved quickly through the water column in search of soft prey.
According to Bicknell, “previous conceptions were that these animals would have seen the Burgess Shale fauna as a smorgasbord, going after anything they wanted to.” However, “we’re finding that the dynamics of the Cambrian food webs were likely much more complex than we once thought.”
More information: Raptorial appendages of the Cambrian apex predator Anomalocaris canadensis are built for soft prey and speed, Proceedings of the Royal Society B: Biological Sciences (2023). DOI: 10.1098/rspb.2023.0638. royalsocietypublishing.org/doi … .1098/rspb.2023.0638
