Oldest known fossil of Rossellids (Hexactinellida, Porifera) from the Ordovician–Silurian transition of Anhui, South China

Abstract

Rossellids are geographically widespread in the modern deep-water sponge community. They are referred to Lyssacinosida, characterized by hypodermal pentactines and choanosomal megascleres of hexactines and diactines or the latter only. The fossil records of rossellids are usually found in the Cenozoic, with the earliest existence known from the Upper Cretaceous, later than the molecular phylogenetic result. A new lyssacinosan hexactinellid, Palaeorossella sinensis gen. et sp. nov., is described from the uppermost Ordovician of Anhui, South China. The sponge shows a saccular, globular or oval form with relatively thick wall. The skeleton is lyssacine type mainly composed of hexactines and stauractines, with the outer margin reinforced by hypodermal pentactines, which usually protrude the periphery as prostalia lateralia. The new species is well-preserved with typical hypodermal and prostalia pentactines as well as an articulated skeleton, giving some tentative insights into the affinity between the new species and other taxa in Rossellidae. It represents the oldest record of rossellids, providing new information for understanding the phylogeny of rossellids and on the evolution of modern Hexactinellida.