Problematic Porifera from the Lower Cambrian of Western Mongolia

A new species of problematic microfossil of the genus Aetholicopalla Conway Morris in Bengtson et al., 1990 is described from the lower Tommotian (lower Cambrian) of the Hevte-Tsakhir-Nuruu Ridge in Western Mongolia. These microfossils are sometimes dominant in Early Cambrian taphocoenoses. A. grandipora sp. nov. is a spheroidal organism with an initially carbonate (?) skeleton; planktonic and benthic forms are described; the latter are variable in shape and substrate attachment sites. The outer wall of the fossils is perforated, thin, double; the functional implication of the pores is unclear; an internal cavity is present. These organisms were probably filter feeders. Geochemical analysis of various taphomorphs showed that A. grandipora sp. nov. are preserved because of phosphate and siliceous mineralization at the early stages of fossilization. Based on a set of observed characters Aetholicopalla is assigned to the earliest skeletal Porifera, of unclear systematic position; perhaps these were juveniles of organisms related to archaeocyaths.