Biogeography, ecology and extinction of Silurian and Devonian tentaculitoids

The paleogeographic history of Silurian–Devonian tentaculitoids is assessed using qualitative data. Base on the recent paleogeographic reconstructions, tentaculitoids expanded their geographic range from the Llandovery to the Wenlock, and remained constant throughout the Ludlow and Pridoli. It increased dramatically thereafter, attaining a maximum in the Early Devonian, followed by a progressive decline until their Famennian extinction. The variation in range is coincident with that of the normalized generic diversity of tentaculitoids, and opposite to that of global sea level. Gotlandellites is the oldest known genus of tentaculitoids having originated in the Llandovery in Europe. Conchs of dacryoconarids gradually evolved from bilateral to radial symmetry in the Early and Middle Devonian. All occurrences of these organisms were restricted to tropical latitudes. The ecological effect of the invasive species is proposed to be a considerable threat for the extinction of tentaculitoids in the Late Devonian. Possible connections between tentaculitoid migrations and paleogeographic environments have been briefly depicted.