Ancient Sea Monsters

A prehistoric leviathan that represents the largest known sperm whale on Earth once hunted smaller whales around 12 million or 13 million years ago, researchers say. Fossils of the whale's skull and foot-long teeth found in Peru suggest the monstrous sperm whales ranged in size from almost 43 feet to 59 feet, or longer than a school bus. Just the skull alone reaches a length of almost 10 feet. <a href="http://www.foxnews.com/scitech/2010/06/30/gigantic-prehistoric-whale-hunted-whales/">Read more. </a> (C. Letenneur (MNHN))

Artist's rendition of a 45-ton pliosaur -- nicknamed Predator X for its tremendous size -- attacking a plesiosaur. (Natural History Museum, University of Oslo, Norway)

Fossils from a real-life sea monster -- a massive crocodile-like species -- were unearthed in Patagonia, Argentina. The animal likely measured 13 feet long from nose to tail. <a target="_blank" href="http://news.nationalgeographic.com/news/2005/11/photogalleries/godzilla/index.html">Read more at National Geographic</a>. (National Geographic)

Computer images of the skull of the crocodile-like marine reptile show how the massive predator might have looked. The researchers who made the discovery say Dakosaurus andiniensis, nicknamed Godzilla, lived about 135 million years ago. <a target="_blank" href="http://news.nationalgeographic.com/news/2005/11/photogalleries/godzilla/">Read more at National Geographic.</a> (National Geographic)

A pliosaur crushes down on a smaller plesiosaur, thanks to its 33,000-lb bite. Plesiosaurs, which existed between 210 and 65 million years ago, and used powerful flippers to fly through the water. Members of another plesiosaur group, popularly known as pliosaurs, had short necks but relatively massive skulls. (Natural History Museum, University of Oslo, Norway)

Artist's interpretation of a pliosaur -- dubbed "Predator X" when its skull was first found in Oslo -- catching a pterosaur. Pliosaurs probably ate whatever they could get a hold of. Some had heads as long as 3 meters and a mouth filled with cucumber-sized teeth that could rip apart almost anything they sunk into. (Natural History Museum, University of Oslo, Norway)

Artist's interpretation of the monster hunting ichthyosaurs. (Natural History Museum, University of Oslo, Norway)

Plesiosaurs were a group of marine reptiles that evolved from land-living reptiles in the Triassic period about 210 million years ago. They too, like ichthyosaurs had four flippers, a remnant of their terrestrial ancestors. (Natural History Museum, University of Oslo, Norway)

An artist's illustration depicts Guarinisuchus munizi going after a tasty nautilus, a still-existing form of cephalopod related to octopuses and squid, 62 million years ago. (Rio de Janeiro Federal University)

A fossil of a prehistoric crocodile species, Guarinisuchus munizi, during a press conference at National Museum of the Rio de Janeiro Federal University in Rio de Janeiro in 2008. Brazilian scientists say they have found a prehistoric crocodile species that inhabited the Earth's oceans some 62 million years ago. (AP)

A model of a prehistoric crocodile species, Guarinisuchus munizi, during a press conference at National Museum of the Rio de Janeiro Federal University in Rio de Janeiro in 2008. Brazilian scientists say they have found a giant prehistoric crocodile species that inhabited the Earth's oceans some 62 million years ago. (AP)

A fossil of a new prehistoric crocodile species, Guarinisuchus munizi, during a press conference at National Museum of the Rio de Janeiro Federal University in 2008. Brazilian scientists said they have found a prehistoric crocodile species that inhabited the Earth's oceans some 62 million years ago. (AP)

This pointy-nosed prehistoric crocodile species inhabited the Earth's oceans 62 million years ago. Brazilian scientists unveiled a model of the three-meter 9 foot long Guarinisuchus munizi in 2008. Scientists say the discovery sheds light on the evolutionary history of the extinct group, a predecessor to modern crocodile species. (Rio de Janeiro Federal University)