Bilateral Oral Structure in a stem-group Euarthropod: Pambdelurion whittingtoni Budd, 1998 Did Not Possess a Radial Oral Cone.

Konservat-Lagerstätten of the Cambrian Period have been instrumental in recent years for studying stem-groups of many different animal phyla. Lobopodians represent an important grade on the stem of the most successful phylum today, Eurthropoda. The giant lobopodian Pambdelurion whittingtoni of North Greenland’s Sirius Passet was an apex predator of the time, with lobopodous limbs and large anterior appendages for grasping prey. Previous reconstructions have suggested that Pambdelurion possessed a radial oral cone constructed from plates, similar to radiodonts such as Anomalocaris. However, these conclusions were based on inarticulated oral plates, with a radial structure being inferred from similar structures in radiodonts and other lobopodians. New specimens, described here for the first time, reveal the complete structure of the animal’s mouth as a bilateral, apparatus distinct from the mouthparts of radiodonts and euarthropods. This structure is also known from the related lobopodian Omnidens ampulus, previously shown to bear similar oral plate morphology. We redescribe the Pambdelurion oral apparatus and give a formal overview of the species based on several nearly complete individuals. The oral morphology is compared and contrasted with that of O. ampulus, discussing implications for the evolution of mouthparts in more crownward radiodonts and euarthropods.