Anomalocaris - Ecology

Ecology

Anomalocaris had a cosmopolitan distribution in Cambrian seas, and has been found from early to mid Cambrian deposits from Canada, China, Utah and Australia, to name but a few.

A long-standing view holds that Anomalocaris fed on hard-bodied animals, including trilobites. While its mid-gut glands strongly suggest a predatory lifestyle, its ability to penetrate mineralised shells has come under fire in recent years. Some Cambrian trilobites have been found with round or W-shaped "bite" marks, which were identified in shape with the mouthparts of Anomalocaris.

Stronger evidence that Anomalocaris ate trilobites comes from fossilised faecal pellets, which contain trilobite parts and are so large that the anomalocarids are the only organisms large enough to have produced them. However, since Anomalocaris lacks any mineralised tissue, it seemed unlikely that it would be able to penetrate the hard, calcified shell of trilobites. One possibility is that anomalocarids fed by grabbing one end of their prey in their jaws while using their appendages to quickly rock the other end of the animal back and forth. This produced stresses that exploited the weaknesses of arthropod cuticle, causing the prey's exoskeleton to rupture and allowing the predator to access its innards. This behaviour is thought to have provided an evolutionary pressure for trilobites to roll up, to avoid being flexed until they snapped. However, the lack of wear on anomalocarid mouthparts suggests they did not come into regular contact with mineralised trilobite shells. Computer modeling of the Anomalocaris mouthparts suggests they were, in fact, better suited to sucking on smaller, soft-bodied organisms (and could not have been responsible for many trilobite deformations).

The mouthparts of Anomalocaris are in fact not tetraradial like those of Peytoia, but have three major axes and a small central opening; thus this species probably fed by sucking up small items rather than biting hard-bodied organisms.