Imagine you are driving down I-5, just north of Bakersfield, in California’s hot and dusty central valley. Except that it’s the Cretaceous Period, 80-65 million years ago, and the central valley is actually an inland sea. And instead of seeing cows standing by the side of the highway, you see mosasaurs swimming through the salty water.
Mosasaurs were marine reptiles that lived during the late Cretaceous, in oceans all over the world. They had fins on their long bodies, and sharp teeth in their long jaws. They ate fish, ammonites, and possibly even other mosasaurs. Lucky for us, mosasaurs are now exctinct — they died out with the dinosaurs at the end of the Cretaceous.
This particular fossil was found in 1937 by a high school student named Allan Bennison. Just the previous year, Bennison found the first dinosaur fossil in California. He used to ride his bicycle from his home in the San Joaquin Valley to the Moreno formation, where this fossil was found, a distance of 35 miles. Bennison went on to study at Berkeley, where he earned a degree in paleontology in 1940. This species was named after him: Plotosaurus bennisoni.