An oversized, late-surviving reticulosan sponge from the Carboniferous of Ireland

Abstract

Cyathophycus is one of the most widespread reticulosan sponges in Ordovician to Devonian rocks, but was mostly limited to the Iapetus region during the Ordovician and Silurian periods. Having an unfused skeleton, these sponges require an element of exceptional preservation (abrupt burial as a minimum) to enter the fossil record. Most species are a few centimetres in size, and found in muddy offshore environments. A new species of Cyathophycus, C. balori nov. sp., from the Kilkee Cyclothem of the Namurian Central Clare Group of County Clare, Ireland, substantially extends the stratigraphic range of the genus into the upper Palaeozoic. At more than 50 cm in height, the new species is the largest known Cyathophycus, and one of the largest reticulosan sponges. The sponges are found abundantly as monospecific assemblages in a particular band of laminated mudstone in prodelta cyclothem deposits. This unexpected discovery reveals a new component to Carboniferous prodeltaic ecosystems, and is further evidence that early sponge groups persisted in some unusual and marginal environments.