The Maastrichtian Cretaceous Mosasaurs of Morocco

Mosasaurids (Squamata) from the Maastrichtian Phosphates of Morocco: Biodiversity, palaeobiogeography and palaeoecology based on tooth morphoguilds

Authors:

Bardet et al

Abstract:

Mosasaurid squamates are the most numerically abundant, and taxonomically/ecologically diverse clade of marine amniotes represented in the Maastrichtian Phosphates of Morocco. With few exceptions, they are faunally typical of the Southern Mediterranean Tethys Margin (around palaeolatitude 25°N) and range from the base to the top of the stage. The Moroccan assemblages include at least 7 genera and 10 species representing a broad spectrum of sizes and morphologies that illustrate several ecological trends. Noteworthy is the predominance of Mosasaurinae which are widespread in contemporaneous outcrops worldwide and constitute 80% and 70% of the total genus/species number respectively. In contrast, Halisauromorpha and Russellosaurina (plioplatecarpines) are scarce and tylosaurines are presently unknown. All of the Moroccan mosasaurids exhibit characteristic tooth morphologies and can be placed into resource partitioning morphoguilds indicative of adaptations for piercing, crushing or cutting. Medium to large predators are found to distribute along the ‘Crush’-‘Cut’ axis of the morphoguild projection, and a new ‘Crush-Cut’ guild, previously unrecognised amongst Mesozoic marine amniotes, accommodates several Prognathodon species. Also of importance is the lack of mosasaurids along the ‘Pierce’-‘Crush’ axis, potentially inferring that these ecological niches were occupied by other marine vertebrates such as selachians and plesiosaurs. In addition, the relative abundance of mosasaurids throughout the Maastrichtian series of the Gantour Basin evidences direct ecological competition or predation phenomena.