The oldest skeletal macroscopic organism Palaeopascichnus linearis

The existing problems regarding the phylogenetic resolution of Ediacaran macroscopic organisms stem from a failure to factor-in the information captured through different ‘taphonomic windows’. Here we integrate the information from sandstone- and limestone-hosted occurrences of the fossil Palaeopascichnus linearis that together show a conspicuously greater range of taxonomic and taphonomic variation. The limestone- hosted material comes from a new locality discovered on the northwestern slope of the Olenek Uplift in Arctic Siberia that characterises the uppermost Ediacaran strata of the Khatyspyt Formation, Khorbusuonka Group. Detailed taphonomic and morphodynamic studies of the fossil material revealed evidence of possible chamber wall agglutination and growth through addition of new chambers with little sideway growth. Palaeopascichnus linearis outlived the intra-Ediacaran (~ 550 Myr ago) drop in species richness, the advent of bilaterians, and the increase in complexity of burrowing behaviour in metazoans. It remains to be seen whether or not the remarkable ecological success achieved by Palaeopascichnus linearis during the times of rich evolutionary experimentation has anything to do with the invention of an agglutinated test. Palaeopascichnus poses major scientific challenges, and it is now clear that such preservation as occurs in Siberia may hold the answer to what they were, how they lived and what they were related to.