The systematics and evolution of Cambrian graptolites from the Burgess Shale of Canada
Pterobranchs originated in the basal Cambrian (Fortunian) and are mostly known by their tubes preserved in the fossil record. The earliest forms represent bushy erect growing colonies that are not widely studied due to preservation quality and species misidentification. For this reason, basal phylogenetic relationships within the group are not clearly established. Middle Cambrian Burgess Shale graptolites were poorly known from the presence of Chaunograptus scandens, some debatable species of the genus Yuknessia, and other undetermined fragmented material. This study represents a complete description of C. scandens, a consensus for Yuknessia simplex and Y. stephenensis, and the new report of Protohalecium hallianum and Mastigograptus sp. from the locality, which have also been found in Burgess Shaletype localities in Utah and Australia. Phylogenetic analyses of 34 discrete morphological traits from these Burgess Shale genera and some known benthic and planktic taxa (n=22), place these Cambrian species as basal forms between the pseudocolonial pterobranch Cephalodiscus and the living graptolite Rhabdopleura.
Hemichordata Pterobranchia graptolites Burgess Shale paleontology Paleozoic Cambrian systematic