Lizards and snakes belong to the order squamata. Like all reptiles they rely on the environment to regulate their body temperature. Although today their range is limited to warmer regions, fossil lizards have been found on every continent including Antarctica. Fossil snakes first appeared about 100 MYA, but are quite rare in the fossil record. Mosasaurs are an ancient relative of the modern day varanid lizard, which includes the Komodo Dragon. Mosasaurs had a streamlined body similar in shape to the varanid lizards, with much abbreviated limbs. Their powerful tail was swept side to side, in an undulating motion, which allowed them to swim through the water in a manner demonstrated today by the crocodilians. These reptiles were abundant throughout the Late Cretaceous, and varied in size from just a few inches to nearly 50 feet long.
The Cretaceous Period was a time in which warm epicontinental seas were prevalent, one of which, was the Western Interior Seaway. This inland sea stretched from the Western Rockies to the Eastern Appalachians, about 1000 km wide, and connected the Arctic Ocean with the Gulf of Mexico. Many marine reptiles including mosasaurs have been discovered in the sediment left behind by this ancient seaway.
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