Hot fossils in a cold land : early Cambrian stem group bilaterians from Antarctica

During the critical period of expansive biotic radiation in the early Cambrian, Antarctica and southern Australia where sutured together near the equator forming East Gondwana. The rocks deposited during this interval provide ample evidence of a shared geological, palaeontological and palaeogeographic heritage. However, there has been almost no previous systematic sampling of lower Cambrian fossiliferous successions forphosphatic shelly fossils, which have proven so important in providing a chronological framework for understanding the early evolution, ecology and biogeography of bilaterian animals. The retrieval of such faunas provide raw material for investigating the morphological diversity and phylogeny of early (stem group) bilaterians as well as provide a means to under take detailed biostratigraphic correlation between lower Cambrian sequences packages in Antarctica and South Australia. To this end, detailed sampling along stratigraphic sections measured through autochthonous, fault repeated, lower Cambrian carbonate succession of shallow water carbonate platform complete with peri-reefal bioherms in the Shackleton Limestone and overlying carbonate ramp and slope transition in the Holyoake and lower Starshot Formations has produced a moderately diverse fauna of shelly fossils including chancelloriids, sponge spicules, helcionellid molluscs, cupitheciids, hyolithelminth tubes, echinoderm ossicles and the acrotretoid brachiopod species Vandalotreta djagoran, as well as the obolide Eodicellomus elkaniiformis. This newly discovered fauna provides direct correlation to the Wirrealpa and Aroona Creek Limestones in the Flinders Ranges (Arrowie Basin), South Australia and suggests a Toyonian (Cambrian Series 2, Stage 4) age for the upper Shackleton Limestone in the Holyoake Range.1 page(s