The earliest known Fenestrate Bryozoan, with a short review of Lower Ordovician Bryozoa

Silicified residues from the late Arenig Tourmakeady Limestone of County Mayo, Ireland, contain a new bryozoan, Alwynopora orodamnus gen. et sp. nov. Colonies have erect branches bearing two rows of alternating zooecial apertures on their frontal surface and barren of apertures on their reverse surface. Branches bifurcate irregularly, successive bifurcations tending to be approximately in the same plane. There is a strong gradient of branch thickening towards the colony base. Alwynopora is the earliest known bryozoan of the Order Fenestrata. The occurrence of bryozoans in the lower Ordovician is briefly reviewed; the thirty-eight taxa described have an extensive taxonomic distribution, are morphologically diverse, and geographically widespread.