Where did ancient marine lizards give birth?

Mosasaurs, aquatic Mesozoic lizards that went extinct at the end of the Cretaceous period, reached sizes of over 13 meters. Considered a top predator, mosasaurs were air breathing ancient creatures that gave birth to live young. The presence of extremely young mosasaurs in an open water supports the idea that the Mososaurs gave birth to live young that were fully fledged swimmers able to survive alongside adults.


Figure. Artist’s interpretation of this study’s principal conclusions, illustrating Clidastes liodontus giving live birth in an open pelagic setting ~85 million years ago, beneath the shadow of the toothed stem bird Ichthyornis. Illustration by Julius Csotonyi.


The research, published online this week in Palaeontology, examines small specimens from the Niobrara Formation of Kansas, originally misclassified, bolstering evidence of mosasaur live birth in the open ocean rather than on or near the coast. The specimens used to draw this conclusion were none other than dental records. The presence of the secondary bonelike connective tissue covering the root of a tooth, osteocementum, and position of replacement pits at base of the tongue were just one of the items researched to indicate that Mosasaurs gave live birth at sea.