Hurdiid radiodontans from the middle Cambrian (Series 3) of Utah

Abstract

AbstractRadiodontan body elements, some belonging toPeytoiaandHurdiaand some unassigned, have been reported from the Langston Formation (Spence Shale Member), Wheeler Formation, and Marjum Formation of the middle Cambrian (Series 3) of Utah. These identifications are reassessed in light of recent work on the morphology of the radiodontanHurdia. New specimens ofHurdiaare identified from the Spence Shale, representing mouthparts (oral cones), cephalic carapace H-elements, frontal appendages, and a single isolated swimming flap. The shape of the H-elements allowsH. victoriaWalcott, 1912 to be identified from the Spence Shale for the first time. The flap is larger and more complete than any reported from the Burgess Shale and allows for a better understanding of the morphology ofHurdiaswimming flaps. A 3D model of aHurdiafrontal appendage indicates that there is only one morph ofHurdiafrontal appendage found in both species, and apparent morphological differences between disarticulated appendages reflect a preservational continuum caused by varying oblique angles relative to the seafloor.Peytoiashould no longer be reported from the Spence Shale, but its presence is confirmed in the Wheeler and Marjum formations. New mouthparts (oral cones) ofHurdiafrom the Spence Shale andPeytoiafrom the Marjum Formation with surface textures of submillimeter-diameter raised nodes are described. These new features have not been observed in material from the Burgess Shale and suggest slight differences in preservation.