Adaptations to changing substrates in diploblastic dinomischids from the early Cambrian.

The significant changes in seafloor conditions during the Ediacaran-Cambrian transition presumably bear on the autecology of the benthic animals living in this time interval. However, little evidence shows morphological modifications and life strategy transitions in early animals in response to this substrate revolution. Dinomischidae is a family of diploblastic-grade with a sessile, suspension-feeding lifestyle, which includes Xianguangia , Daihua and Dinomischus. Here, we redescribe Calathites spinalis , a poorly known taxon from the early Cambrian (Epoch 2, Age 3, ∼518 Ma), as a new member of this family. Our new material reveals that the body of C. spinalis consists of a stalked calyx and 18 tentacle-sheath complexes, which is a typical trait of dinomischids. Our phylogenetic analyses recover Calathites as a sister group of Xianguangia and Daihua and support dinomischids being a monophyletic group. Members of dinomischids possess unique attachment structures that vary in shape and size, presenting a unique example of morphological adaptations of early sessile animals during the Cambrian substrate revolution. Comparison with early metazoan fossils reveals that dinomischids and other early basal metazoans lagged behind sessile bilaterians in terms of adaptations to substrate changes; the former tends to persist with attachment strategies adapted to Proterozoic-style seafloor conditions that were relatively firm. [Display omitted] • Exquisite fossils of Calathites exhibit traits typical of dinomischids. • Dinomischids have diverse types of attachment structures. • Dinomischids are categorized as shallow sediment stickers adapted to firm Proterozoic-style seafloor conditions. • Insights into adaptations of Chengjiang sessile metazoans to the Cambrian substrate revolution. [ABSTRACT FROM AUTHOR]