Mouths and Arms

James St. John - (Burgess Shale Formation, Middle Cambrian;
Walcott Quarry, above Field, British Columbia, Canada)

The grasping appendage, sometimes called an arm, of Anomalocaris was approximately 45.72 cm (18 in) long and covered in spiky barbs. The arms and the spiky barbs would have served two important uses in the feeding behavior of the Cambrian predator: 1) to grasp and hold prey items and 2) to move the food near and into the mouth of Anomalocaris. These long grasping appendages, in coordination, with the large compound eyes made Anomalocaris an accurate predator, though of course we do not have any way to gauge its actual capture rate. Dragonflies, in the world of extent arthropods, are the most successful hunters with a prey capture rate that is approximately 95%. The current apex predators of the ocean, Great White Sharks and Orcas, have widely variable hunting success rates that are reported between 48% (for Great White Sharks) and 95% (for Orcas). Anomalocaris could have fallen anywhere in this range, but was most likely fairly successful given its high mobility, articulate (appearing) arms, and compound eyes. The mouth, of course, had quite an impact on the feeding capabilities of Anomalocaris as well.

James St. John - Anomalocaris canadensis mouthpiece
(~5.25 x ~4.25 cm) from the Walcott Quarry, Burgess Shale

The mouth of Anomalocaris consisted of 32 oral plates that have, multiple times, been compared to pineapple rings. The plates were constituted of 4 large and 28 small interlocking plates that were ringed internally by denticulate prongs that, thanks to multiple specimens, have been observed stretching down the entire gullet of the animal. This ring, save where the denticulate prongs would meet or occlude, was capable of closing and crushing, effectively biting in a circular motion, the trilobites that it shared the Cambrian waters with.