Problematical Porifera from the Lower Cambrian of Western Mongolia

Abstract

From the lower part of the Tommotian Stage of the Lower Cambrian of Western Mongolia, ridge Hevte-Tsakhir-Nuruu described a new species of problematical microfossils of the genus Aetholicopalla Conway Morris in Bengtson et al., 1990, whose representatives are sometimes the dominants of the Early Cambrian taphocoenoses. A. grandipora sp. nov. – spheroidal organisms with initially carbonate (?) skeleton; planktonic and benthic forms described; the latter have a variable shape and attachment sites to the bottom substrate. The outer wall of the fossils is perforated, thin, double; the functional implication of the holes is unclear; be present an internal cavity. By mode of existence, these organisms were probably filter feeders. Geochemical analysis of various taphomorphs showed that A. grandipora sp. nov. preserved by phosphate and siliceous mineralization in the early stages of fossilization. The set of recognized characters allows us to attribute Aetholicopalla to the first skeletal Porifera of an unclear taxonomic position; perhaps these were juvenile forms of organisms close to archaeocyates.