PUTTING ANOMALOCARIS ON A SOFT-FOOD DIET?
In life, anomalocaridid mouth plates were connected along their long edges by flexible tissue, and mouth plates, esophageal plates and preoral appendages were composed of unmineralized cuticle. The mouth could close like a sphincter, and its plates could have moved synchronously or moved asynchronously with opening initiated by four large cardinal plates. Whether moving in an inverted, everted, or in-plane position, a rapidly closing anomalocaridid mouth could generate sufficient external pressure change to allow suctorial feeding - yet no anomalocaridid mouth could close more than half-way.
To test the hypothesis that anomalocaridids ate trilobites, we conducted finite element analyses of how different biting stresses would deform and cause failure of twelve commonly malformed Cambrian trilobites. A spectrum of trilobite sizes, shapes, thicknesses, and ornamentation were subjected to both horizontal and vertical bite-impact angles, using the known range of anomalocaridid plate tip sizes. Young’s modulus, Poisson’s ratio, and ultimate tensile strength were derived from strain measurements on modern marine arthropod cuticle ranging from freshly molted Callinectes sapidus to well sclerotized claws of Homarus americanus. These cuticle material properties were applied to each possible combination of anomalocaridid biting geometry and trilobite type. In the absence of significant bending stresses, cuticle failure always occured at the locus of bite impact in all trilobites modeled; where bending stresses predominated, failure occurred near the axial furrow. FEA suggests that although tiny or protaspid trilobites could be eaten whole by most anomalocaridids, and some freshly molted trilobites could possibly be deformed by interacting with anomalocaridid mouth plates or preoral appendages, anomalocaridid mouth plates would break before most trilobite thoracic cuticle would fail.