EXPLORING ANOMALOCARIS RAPTORIAL APPENDAGES WITH 3D KINEMATICS

Radiodonts—stem-lineage arthropods with paired frontal, often raptorial, appendages and an oral cone—are often considered predators. Anomalocaris canadensis in particular, has been described as an apex predator within the Burgess Shale biota and capable of durophagy, potentially aided by its appendages. By extension, A. canadensis and other closely related Cambrian radiodonts have been implicated to explain injuries in Cambrian trilobites. However, the range of appendicular motion and the effectiveness of A. canadensis in grabbing prey with its frontal appendages remains somewhat unsubstantiated. We have conducted the first 3D kinematic analysis of a radiodont frontal appendage using A. canadensis as the model taxon, drawing on the level of detail afforded by abundant and exceptionally well-preserved Burgess Shale specimens. Two A. canadensis models are considered—a conservative approach that limits the range of motion to that afforded by the arthrodial membranes between each of the 14 podomeres, and a more realistic model allowing nesting of podomeres that more closely replicates the closure observed in fossil material. These models are compared to two modern arachnid analogues with large raptorial appendages, a whip spider and a whip scorpion. These analyses show that A. canadensis likely flexed its appendages in a similar way to arachnid pedipalps, gripping and holding prey within its pointed endites before passing it to the mouth. The simulated range of motion does not support the dexterity needed to manually weaken and crack open mineralized trilobite exoskeletons. These results further allow us to refine the interpretation and reconstruction of the head region of A. canadensis, in line with a realistic estimate of its feeding functional morphology.