Mosasaurs

Mosasaurs were real life leviathons and the apex predators of the late Cretaceous oceans. It's a common misconception that Mosasaurs are swimming dinosaurs, when in fact they are marine reptiles.

Around 98 million years ago, during the mid-Cretaceous period, a family of lizards related to modern day monitor lizards began returning to the oceans, these lizards would go on to evolve into marine reptiles called Mosasaurs. Ichthyosaurs and Pliosaurs were the dominant predators in the world's oceans during the mid-cretaceous, however their reign was brought to an abrubt end by an extinction event caused by underwater volcanic activity around 92 million years ago. This left a huge gap in the oceanic food chain, one which Mosasaurs quickly filled.

Mosasaurs mushroomed into a variety of forms, some growing to the size of whales and feasting on large prey, while others adapted rounded teeth for crushing shells. Never before had a marine reptile group achieved so much diversity in such a short time.

Mosasaurs would go on to be the last major group of reptiles to make the transition from land to sea.  They reigned over the world's oceans for the last 25 million years, before going extinct in the catasrophic mass extinction event at the end of the Cretaceous period.

The Mosasaur fossil you've scanned come from the Ouled Abdoun Basin, located west of the Atlas Mountains near the city of Khouribga in Morocco. The area has huge phosphate deposits, which formed over a period of 25 million years at the end of the Cretaceous and early Eocene, and is famous for its abundance of marine fossils. Those fossils include the remains of mosasaurs, plesiosaurs, crocodiles, sharks, fish and a small number of terrestrial animals which were washed out to sea.