Tylosaurus, a Mosasaur

© Michael Skrepnick

Mosasaurs like this one were among the largest predators in the ancient ocean. Scientists know the animal could dive to great depths because its eardrums are surrounded by thick bony rings to protect against water pressure. Some mosasaurs were huge; the animal on display was probably about seven meters (23 feet) long, and its largest relatives were nearly three times longer.

Their size is amazing, but so is the way these ancient sea-going squamates resemble today's Monitor Lizards and snakes. For instance, Platecarpus could swallow prey larger than its head, thanks to jointed, flexible jaws; some lizards and most snakes have the same trait. Platecarpus had two complete sets of top teeth, one in its jaws and another in the roof of its mouth; many modern squamates have the same arrangement. Platecarpus replaced its teeth throughout life; so do most lizards and all snakes.

• Bony ring around eardrums
• Second set of teeth
• Replacement teeth
• Joint in side of lower jaw