Mosasaurs are a group of aquatic squamates which dominated marine environments during the Late Cretaceous (~100–66 Mya) and dramatically radiated during the latest Cretaceous (Campanian–Maastrichtian: 83.6–66 Mya). Mosasaur fossils from the Maastrichtian of Denmark are scarce, and have only been sporadically studied despite substantial interest in vertebrate biodiversity prior to the Cretaceous-Palaeogene (K/Pg) mass extinction. A comprehensive taxonomic re-examination of the Danish material reveals the coexistence of four mosasaurines (Mosasaurus hoffmanni; M. lemonnieri?; Prognathodon sp.; Carinodens minalmamar) and one plioplatecarpine (Plioplatecarpus sp.), with M. lemonnieri? previously unknown from the assemblage. The relatively high taxonomic richness, as well as new evidence for neonatal mosasaurs, indicate that a diverse mosasaur fauna inhabited the Boreal ‘Chalk Sea’ throughout the Maastrichtian. Tooth shape variation hinted at the occupation of several ecological guilds. Spectrometry-based analyses of enamel samples, examining strontium and barium concentrations relative to calcium, provided further evidence for partitioning between presumed macrophagous apex predators and taxa occupying lower trophic levels. By integrating geochemical and morphological data, our findings point to the persistence of high ecological disparity in Boreal Realm mosasaurs through to the final 50,000 years of the Cretaceous, abruptly terminating at the K/Pg boundary.
Voiculescu-Holvad et al. (Thu,) studied this question.