Russellosaurus

Russellosaurus is the oldest well-preserved mosasaur skull ever found in North America, at about 92 million years old.12

The only known fossil is a nearly complete skull, found in 1992 by a fossil hunter named Mark Cohen at a housing construction site.12

This mosasaur was small and lightly built, with a narrow skull and 16 teeth on each side of its upper and lower jaws.2

The skull bones were not fully fused together, and the bone surface had lots of blood vessels, showing the animal was still growing fast when it died.12

Russellosaurus is the name-giver for a whole group of mosasaurs called Russellosaurina, which includes the famous Tylosaurus and Plioplatecarpus.12

It lived alongside another early mosasaur called Dallasaurus, which still had legs and could probably walk on land.2