BIOMECHANICS OF THE MOUTH APPARATUS OF ANOMALOCARIS: COULD IT HAVE EATEN TRILOBITES?

The Cambrian animal Anomalocaris is hypothesized to have eaten trilobites and other biomineralized prey. The lack of broken or abraded teeth on the plates comprising examination of the mouth apparatus of Anomalocaris suggests that it may not have had the ability to break the exoskeletons of any hard-shelled animal. SEM – EDS of the mouth apparatus from Burgess Shale specimens, indicate that the 32 plates are composed of organic carbon, suggesting they were originally unmineralized cuticle.

Mechanical properties of these plates were analyzed using CAD modeling and Finite Element Analysis. Poisson's ratio and Young's modulus of potential Anomalocaris plates, as well as density and fracture strength used for the FEA analyses, were estimated using a range of modern-day arthropods. Two end-member values were used both to approximate the range of strengths exhibited by Anomalocaris' cuticle, and also to encompass the range of exoskeleton strength likely exhibited by trilobites. The hardest skeletal values are from wet lobster (Homarus americanus) crusher claw cuticle; these are most likely to deform in a brittle manner. The softest are from adult dung beetle (Copris ochus) cuticles. In order to bite and successfully break the calcified cuticle of a trilobite, Anomalocaris' mouth plates would have needed to withstand forces that are greater than those required to fracture a trilobite exoskeleton. Results demonstrate that the teeth-like structures of the mouth plates should have deformed or broken when less than 90 N of force was applied perpendicular to the plates.

Additionally, documented trilobite malformations were compared to modern and extinct arthropod malformations. Abnormal trilobites previously attributed to predation of Anomalocaris might also be interpreted as molting failures or genetic mutations; such malformations occur with similar frequency in modern marine clawed lobsters, brachyuran decapods, and limulids. Furthermore, there is no direct evidence for Anomalocaris' feeding habits such as gut contents.