Archelon

Archelon was a huge marine turtle (Testudines) that was the size of a car. It lived in North America 74 million years ago (from the Upper Cretaceous) in the epeiric inland sea called the Western Interior Seaway. Fossils have been found in the U.S. states of Kansas and South Dakota. 
This carnivore was up to long. It had a wide, flattened shell, paddle-like legs, a long, narrow head, weak jaws, and a short, pointed tail. Its only predators were probably the larger mosasaurs. From its beak, its own food was probably squid.
"Archelon", like other turtles, had a solidly-roofed skull with no opening (except for eyes, and nostrils).