The Last Marine Reptiles

Rob Barber/AMNH

Cretaceous, 75 million yrs. ago.

During their long reign, dinosaurs were the top predators on land. In the oceans, meanwhile, three groups of large reptiles more closely related to lizards and snakes dominated the food chain, eating fish and other animals. All three groups, plesiosaurs, ichthyosaurs and mosasaurs, went extinct around 65 million years ago.

Illustration © Doug Henderson

Plesiosaur.

Illustration © Doug Henderson

Mosasaur.

Extinct

Plesiosaurs: During the Jurassic period (199.6 to 145.5 million years ago), the largest plesiosaurs were the top ocean predators.
Ichthyosaurs: These graceful marine reptiles looked somewhat like dolphins--but were more closely related to lizards and snakes.
Mosaurus: The marine lizards known as mosasaurs were notable for their long, slender bodies, large skulls and limbs that served as paddles.

Illustration © Doug Henderson

Plesiosaur.

Long Necks

Many of the marine reptiles called plesiosaurs had extraordinarily long necks. One species, Styxosaurus browni, was about 11 meters (35 feet) long--and almost half of its body was neck. Plesiosaurs went extinct at the same time as two other groups of marine reptiles, ichthyosaurs and mosasaurs.

Illustration © Doug Henderson

Mosasaur.

Mosasaurs of the Midwest

During the Cretaceous period, central North America was covered by a large inland sea. The snakelike marine reptiles called mosasaurs were common in these waters, preying on fish and other animals.

Dolphins or Reptiles

The marine animals called ichthyosaurs had fishlike tail fins and gave birth to live young. They resembled dolphins but were reptiles related to snakes and lizards.

Ichthyosaur.

Stenopterysi.