Aquatic reptiles and cephalopods in the Mesozoic period. The Mesozoic Era is an interval of geological time from about 252 to 66 million years ago. It is also called the age of reptiles, a phrase introduced by the 19th century paleontologist Gideon Mantell who viewed it as dominated by reptiles such as iguanodon, megalosaurus, plesiosaurus and what are now called pseudosuchia. Here, the reptiles shown (in order of the heads from left to right) include: plesiosaur and osteopygis, ichthyosaur, teliosaur, plesiosaur, elasmosaur, mosasaur. The cephalopods shown (from left to right) include: ammonite, crioceras, belemnites, baculites, and ammonites. The reptiles are based on Hawkins and Cope's restorations. From "The Story of the Earth and Man," by John William Dawson, 1873.