Johan Lindgren

Remains of late Campanian and earliest Maastrichtian mosasaurs from southern Sweden are illustrated and briefly described. Plioplatecarpus sp. and Prognathodon sp. have been identified from strata of middle late Campanian age, while earliest Maastrichtian deposits contain remains of Mosasaurus cf. lemonnieri and Plioplatecarpus cf. primaevus. Available data suggest that the mosasaur group increased steadily in diversity from the late Coniacian until close to the early/late Campanian boundary, at which a seemingly catastrophic event severely reduced the number of species in, at least, North America and northern Europe. The extinction favoured a radiation of more derived mosasaur taxa which persisted until the end of the Maastrichtian Stage. Although the mechanism responsible for this profound mid-Campanian mosasaur faunal turnover remains unknown, it is clear that the marine reorganization affected markedly different and widely separated environments.