Mosasaurs

Mosasaurs are an extinct group of large marine reptiles in the family Mosasauridae, belonging to the squamate lineage that includes lizards and snakes. They evolved from terrestrial lizards and became specialized marine predators during the Late Cretaceous, with fossil records spanning roughly 100 to 66 million years ago and worldwide geographic distribution.

In appearance, mosasaurs had elongated, streamlined bodies, strong jaws with numerous sharp, conical teeth, and limbs modified into paddle-like flippers. Their tails supported a large fin, facilitating efficient propulsion through water. They varied considerably in size, with many species reaching several meters in length and some estimates exceeding 15 meters.

Most mosasaurs are interpreted as viviparous, giving birth to live young in the ocean. Fossils showing embryos inside adult females provide strong evidence for this reproductive mode, distinguishing mosasaurs from many other marine reptiles that laid eggs on land.

Ecology and diversity: Mosasaurs occupied a range of ecological niches as apex marine predators. Different genera show variation in dentition and skull shape, from long-snouted forms that specialized in fish to robust, crushing dentitions that could tackle hard-shelled or larger prey. They coexisted with plesiosaurs, sharks, and other marine reptiles in Cretaceous seas.

Extinction: Mosasaurs disappeared at the end of the Cretaceous during the K-Pg mass extinction about 66 million years ago, along with many other marine and terrestrial groups. The precise causes are linked to widespread ecological disruption following the asteroid impact and volcanic activity, which altered marine ecosystems and food webs.