How many modern marine reptiles can you name? I count two, broadly speaking: sea turtles and marine iguanas. Back in the Cretaceous, there were a few others. Many of the world’s oceans hosted the deadly mosasaurs, which were essentially marine-adapted monitor lizards. You also had the familiar but puzzling plesiosaurs; with their long necks, tiny heads, and wide rounded bodies, it’s still difficult to determine exactly how they made their living. Also still going strong were the ichthyosaurs—dolphin-shaped marine lizards with huge eyes and a taste for cephalopods. Marine iguanas weren’t a thing yet, but sea turtles were actually more diverse (and bigger) than they are today.