An exceptional caradoc sponge fauna from the llanfawr quarries, central wales and phylogenetic implications

Abstract

Synopsis An abundant sponge collection from basal Caradoc mudstones of the Llanfawr Quarries, Llandrindod, Powys is the most diverse fine‐sediment sponge fauna recorded from the British Palaeozoic. It is dominated by reticulosans, but includes some lyssakids and demosponges. Eight new genera and 11 species are erected and one new family proposed: Xylochos palindromica gen. et sp. nov., Pirania llanfawrensis sp. nov., Heminectere minima gen. et sp. nov., Asthenospongia cambria sp. nov. (Asthenospongiidae nov.), Acutipuerilis spinosus gen. et sp. nov., Granulispongia obscura gen. et sp. nov., Hemidiagoniella tenax gen. et sp. nov., H. caseus sp. nov., Solusrectus rosetta gen. et sp. nov., Cyathophycus loydelli sp. nov., and Dilatispongia tumidus gen. et sp. nov. Some specimens are preserved with organic or pyritic films representing soft tissue and most have high‐fidelity preservation of spicule external moulds, although iron oxide spicule replacement obscures details prior to cleaning. D. tumidus shows a thickened wall with specialised dermalia, while retaining some degree of quadruling and represents a lineage that may have given rise to the brachiospongioids. Others, such as S. rosetta, appear close to the ancestral state of the modern Lyssacinosida. The hex‐actinellid taxa are interpreted in a reasoned phylogenetic framework that stresses the importance of root tuft structure, the presence of zero‐order spicules and the number and nature of spicule layers. It also attempts to link extant and Lower Palaeozoic palaeontological classifications. The parallel evolutionary development of thick walls and strong attachment structures is interpreted as being due to an offshore‐onshore expansion, contrary to many other groups.