Graptolite (Hemichordata,Pterobranchia) preservation and identification in theCambrianSeries 3

Abstract

AbstractDue to inadequate preservation, pterobranchs are often difficult to identify in the fossil record, and a better understanding of preservational modes and diagenetic and metamorphic effects is needed for their recognition. Pterobranch hemichordates are common inCambrianStage 5 and younger sedimentary rocks, but are frequently overlooked. Often, pterobranch hemichordate colonies have been considered to be algal remains or hydroids. Re‐examination ofCambrianBurgess Shale algae reveals that the generaYuknessiaandDalyiacan be recognized as putative early representatives of pterobranch hemichordates. Distinct fusellar construction of the individual zooidal tubes and branching of the creeping proximal part of the colonies are found in the morphologically similar rhabdopleurid pterobranch genusSphenoecium. The erect tubes ofSphenoeciumdo not branch and can reach a length of several centimetres. The development of the fusellar construction in this taxon shows a highly irregular development of the suture patterns, but a fairly consistent height of the individual fuselli. The taxon is widely distributed in theCambrianSeries 3, but has regularly been identified as a hydroid or an alga.Sphenoecium wheelerensisfrom theCambrianWheelerShale ofUtah is described as new.