Ecomorphologie des mosasaures du Crétacé supérieur belge

Abstract

Mosasaurs are a group of squamates that dominated the Upper Cretaceous seas. They show a wide range of morphologies reflecting their adaptations to various ecological niches, yet no quantitative analysis of their ecological diversity exits to date. Belgium and the Netherlands are home to two of the world's largest mosasaur deposits, the first in the Mons basin and the second in the Maastrichtian type area. In this work, quantitative methods (PCoA, Cluster) are applied to a series of morphometric features and measurements taken from twenty-five specimens (representing eight species for five genera) of Belgian mosasaurs, in order to reveal their ecological diversity. The principal coordinate analysis (PCoA), in spite of a small variance explained, made it possible to observe the great disparities shown within the morphospace of mosasaurines; testifying for example of the particularly isolated morphology of Carinodens belgicus, one of the rare taxa regarded as durophageous. These analysis also seem to indicate a convergent morphology between several specimens of plioplatecarpines and mosasaurines. Cluster analysis allow to differentiate four ecological niches, namely: the niche of the apex predators, the niche of the generalists, the niche of the soft prey specialists and the niche of the durophageous. The mosasaurines reveal a significant niche partitioning within the group, showing representatives in the four niches. This work also shows that Mosasaurus lemonnieri seems to experience a niche transition during its growth, passing through three niches during its ontogenesis. The clades Tylosaurinae and Plioplatecarpinae exhibit a low ecological diversity, and seem constrained in the niche of the apex predators for the first and in the niches of the generalists and soft prey specialists for the second. At the scale of the two basins, we observe on both sides the colonization of the four ecological niches by either identical taxa thus revealing a more cosmopolitan trend like Carinodens belgicus and Mosasaurus lemonnieri, either phylogenetically close taxa like Plioplatecarpus houzeaui and Plioplatecarpus marshi, or phylogenetically distant taxa then betraying convergences as between Mosasaurus hoffmanni and Tylosaurus bernardi.