Mosasaurs are aquatic lizards – related to monitors and snakes – that emerged during the early Upper Cretaceous. They evolved rapidly from relatively small ancestors into giant apex predators, rivaling in size present-day whales with total lengths of 15-20 meters. During this evolution their body more and more adapted to the aquatic lifestyle by e.g. reduction of the limbs, elongation of body and tail, and the presence of a tail fluke. They gave birth to fully developed juveniles, which made them independent from the necessity to go on land to lay eggs as most of their relatives.

During the Late Cretaceous, mosasaurs diversified in a large number of genera and species with a global distribution. Main driving factors of this diversification appear to be adaptation to various feeding sources and behaviors. This is best reflected by the variable morphologies of the dentition which can change from blade-like, cutting teeth to blunt, bulbous, crushing teeth suited to feeding on hard-shelled invertebrates and turtles. This ecological variation gives a high level of information even of isolated teeth, which are the most abundant fossils of mosasaurs. The history of mosasaurs terminated abruptly with the global extinction event which marked the end of the Cretaceous.

Research focus on mosasaurs from Germany with a global perspective

In Germany, mosasaur fossils are quite rare and consist only of isolated teeth and bones. This is in sharp contrast to neighboring regions, especially The Netherlands and Belgium from where excellent fossils of complete mosasaurs are known.

Nonetheless a careful analysis of the isolated remains elucidate that Mosasaurs were also diverse and widespread in Germany from the Santonian to the Maastrichtian stages. During this time-span the relative sea-level in north-western Europe (North Sea Basin) underwent an almost continuous rising, flooding most parts of today Germany.

Shallow, nearshore regions during the Santonian and early Campanian were mostly in inhabited by plioplatecarpine mosasaurs (Krüger 2005, Sachs et al. 2017).

Abundancy and diversity of mosasaur peaked during the late lower to upper Campanian in middle to lower shelf deposits, formed in water depth around 70 m (Hornung & Reich 2015, Hornung et al. 2018). They include tylosaurines, mosasaurines, plioplatecarpines and halisaurines (Hornung et al. 2018).

The record became sparser in deposits of the Maastrichtian, which are represented by lower shelf chalk carbonates deposited at 100 m of depth and below. From this time-slice only the genus Mosasaurus is recorded so far (Sachs et al. 2015).

References

Hornung, J.J. & Reich, M. 2015. Tylosaurine mosasaurs (Squamata) from the Late Cretaceous of northern Germany. Geologie en Mijnbouw / Netherlands Journal of Geosciences 94(1): 55-71.

Hornung, J.J., Reich, M. & Frerichs U. 2018. A mosasaur fauna (Squamata: Mosasauridae) from the Upper Campanian (Upper Cretaceous) of Hannover, northern Germany. Alcheringa 42(2) [2019]: 543-559.

Krüger, F.J. 2005. Fossilien aus Lengede. 95pp., Staatliches Naturhistorisches Museum Braunschweig.

Sachs, S., Hornung, J.J. & Reich, M. 2015. Mosasaurs from Germany - a brief history of the first 100 years of research. Geologie en Mijnbouw / Netherlands Journal of Geosciences 94(1): 5-18.

Sachs, S., Hornung, J.J. & Scheer, U. 2017. Mosasaurid and plesiosaurian remains from marginal facies of the lower Campanian (Upper Cretaceous) Bottrop and Vaals formations of western Germany. Cretaceous Research, 87: 358-367.