CAMBRIAN BRADORIIDS (ARTHROPODA): THE TIGER MEETS THE BULL

Bradoriids are extinct Cambrian euarthropods that resemble modern ostracods (https://www.mdpi.com/2076-3263/10/4/119). Newly described bradoriids from Cambrian Stages 3-4 of western North America show great promise for advancing biostratigraphy, paleobiogeography, and studies of the developmental biology of the Cambrian arthropod radiation. Bradoriid taxa reported from the Puerto Blanco Formation of México and the Mural Formation of Canada include Beyrichona sp., Cambroarchilocus tigris McMenamin, 2020, Dielymella? sp., Hipponicharion perforata Skovsted, Balthasar, Vinther and Sperling, 2020, Lianshanella sp., and Pseudobeyrichona taurata Skovsted, Balthasar, Vinther and Sperling, 2020, the latter species bearing a prominent anterior spine on its shields or valves. P. taurata occurs in both Canada and México, and it seems likely that a number of undescribed bradoriid taxa remain to be discovered in the western North American Canadiella Paleobiogeographic Province (named here for the ornate tommotiid Canadiella filigrana (Conway Morris and Fritz, 1984)). Evolutionary changes in shield depth in the bradoriid families Beyrichonidae and Hipponicharionidae have been linked, in terms of developmental biology, to the same genes that control trilobite cephalon width. I propose here an evolutionary transition linking preplete C. tigris (‘the tiger’) to amplete/weakly postplete P. taurata (‘the bull’).