The role of Archaeocyatha in Cambrian biostratigraphy and biogeography
The Archaeocyatha is a group of Cambrian fossils successively considered as cnidarians or sponges or as an independent phylum convergent with many groups lacking clear affinities. Comparisons with Recent calcified sponges discovered in submarine caves have demonstrated that the sponge model is consistent with their structural organization. Thus their systematic position is now agreed as a class within the phylum Porifera, permitting realistic investigations of their comparative physiology and life strategies. Archaeocyatha is an important part of research programmes on the Cambrian System, initiated by different commissions of the IUGS since 1970. Archaeocyathan biozones are available in some key regions. Faunal and palaeocommunities distribution, especially of the reefs they helped build in epeiric seas, and migration pathways constrain Cambrian palaeogeographical reconstructions. A database, using recent compilations of the group, is now online. This free access data source offers specialists a tool, easy to use not only as an identification key but also to establish faunal, geographical and stratigraphical distributions of archaeocyathan genera, and a rapid first step towards Cambrian palaeogeographical reconstructions.