The apex predator of the Cambrian had soft rather than crunchy prey

Biomechanical studies of the arachnid-like front „legs” of the extinct apex predator show that the 2-foot (60 cm) marine animal Anomalocaris canadensis was much weaker than once thought. One of the largest animals to have lived during the Cambrian period, it was probably agile and fast, pursuing soft prey in open water rather than hard-shelled creatures on the sea floor. The study is published in the journal Proceedings of the Royal Society b.

First discovered in the late 1800s, Anomalocaris canadensis — Latin for „strange shrimp from Canada” — has long been thought to be responsible for some of the scarred and crushed trilobite exoskeletons paleontologists have found in the fossil record.

„That doesn’t sit well with me because trilobites have a very strong exoskeleton, which is basically made of rock, while this animal is mostly soft and thin,” said lead author Russell Bicknell, a US postdoctoral researcher. Department of Paleontology, Natural History Museum, University of New England, Australia.

Recent research on the armored, ring-shaped mouthparts of A. canadensis casts doubt on the animal’s ability to process tough food. A recent study set out to investigate whether the predator’s long, spiny front appendages could do the job instead.

The first step by the research team, which included scientists from Germany, China, Switzerland, the United Kingdom and Australia, was to identify A. Found in Canada’s 508-million-year-old Burgess Shale. Using modern whip scorpions and whip spiders as analogs, the team was able to show that the predator’s segmented appendages can grasp prey, extend and flex.

A modeling technique called Finite Element Analysis, a. canadensis was used to show stress and strain points on this grasping behavior, explaining that its appendages are damaged when grasping hard prey such as trilobites. The researchers used computational fluid dynamics to place a 3D model of the predator in a virtual current to predict what body position it might use while swimming.

A combination of these biomechanical modeling techniques—used together for the first time in a scientific paper—A. canadensis than previously hypothesized. This animal may be a fast swimmer, extending its front appendages to zoom in on soft prey in the water column.

„Previous ideas were that these animals would have seen the Burgess Shale fauna as a smorgasbord to go after anything they wanted, but we’ve found that the dynamics of Cambrian food webs were more complex than we once thought,” Bicknell said.