Royseux: a palaeobiodiversity hotspot in the Late Viséan (Carboniferous) of Belgium

1. IntroductionQuantifying biodiversity has become a major concern, not only for modern ecology and nature conservation, but also in the fossil record, where the aim is understanding the effects of global changes on the diversity of past life. During the last decade the palaeontological literature dealing with changes in biodiversity over large time scales (periods, stages) has increased significantly. Unfortunately, most papers failed the difficult task of pinpointing the origin of biodiversity: why so many taxa occur(ed) in a particular area at a particular time, why is the diversity not globally distributed, and why do many taxa occur only in localised areas? Biodiversity hotspots are sites or areas with an unusually high numbers of co-occurring species (Myers, 1988). Present-day biodiversity hotspots are defined as biogeographic areas where the density of co-occurring species is extraordinarily high (Marchese, 2015) and/or as areas with a high density of endemic species, most of which are currently suffering habitat loss (Myers et al., 2000). Although this definition is easily applicable to present biodiversity, it is difficult to recognise ancient biodiversity hotspots and few examples have been recorded (e.g. origin and shift of modern marine tropical hotspots of the Indo-Australian Archipelago: Renema et al., 2008; mollusc palaeo-hotspot in the Lutetian of the Paris Basin: Merle, 2008; endemic crinozoan hotspots in the Pennsylvanian of North America: Waters & Webster,