Plesiosaur Fossils
One of the odd things about plesiosaurs and pliosaurs is that, 100 million years ago, the distribution of the earth's oceans was much different than it is today. That's why new fossils are constantly being discovered in such unlikely places as the American midwest, major portions of which were once covered by the broad, shallow Sundance Sea.
Plesiosaur fossils are also unusual in that, unlike those of terrestrial dinosaurs, they're often found in one, completely articulated piece (which may have something to do with the protective qualities of the silt at the ocean floor). These remains puzzled scientists as long ago as the 18th century; one fossil of a long-necked plesiosaur prompted a paleontologist to quip that it looked like "a snake threaded through the shell of a turtle."
A plesiosaur skeleton also figured in one of the most famous dust-ups in the history of paleontology. In 1868, the famous bone-hunter Edward Drinker Cope reassembled an Elasmosaurus fossil with the head on the wrong end (to be fair, up to that point, paleontologists had never encountered such a long-necked aquatic reptile). According to legend, this error was seized on by Cope's rival Othniel C. Marsh, kicking off a long period of rivalry and sniping known as the "Bone Wars."
Living Plesiosaurs?
Even before a living coelacanth--a kind of primitive fish believed to have died off tens of millions of years ago--was found in 1938 off the coast of Africa, people called "cryptozoologists" have speculated about whether all the plesiosaurs and pliosaurs really went extinct along their dinosaur cousins. Whereas any surviving terrestrial dinosaurs would likely have been discovered by now, the reasoning goes, the oceans are vast, dark and deep--so somewhere, somehow, a genus of plesiosaur might have survived.
The poster lizard for living plesiosaurs, of course, is the mythical Loch Ness monster--"pictures" of which bear a marked resemblance to Elasmosaurus. There are two problems with the theory that the Lock Ness monster is really a plesiosaur: first, as mentioned above, plesiosaurs breathe air, so the Loch Ness monster would have to emerge from the depths of its lake every ten minutes or so, which it certainly doesn't. And second, as also mentioned above, the necks of plesiosaurs simply weren't strong enough to allow them to strike a Loch Ness-like pose.
Of course, as the saying goes, absence of evidence is not evidence of absence. Vast regions of the world's oceans remain to be explored, and it doesn't defy belief (though it's still a very, very long shot) that a living plesiosaur may one day be found. Just don't expect it to be found in Scotland, in the vicinity of a famous lake!
Here's a list of the most notable genuses of plesiosaurs and pliosaurs; just click on the links for more information.
Aristonectes One of the last plesiosaurs left before the K/T extinction.
Attenborosaurus This plesiosaur was named after the documentarian David Attenborough.
Cryptoclidus This mean-looking pliosaur was one of the biggest of all marine reptiles.
Dolichorhynchops A typical pliosaur of the late Cretaceous.
Elasmosaurus From head to tail, the longest plesiosaur that ever lived.
Hydrotherosaurus This "fisherman lizard" roamed the prehistoric coasts of California.
Kronosaurus Makes a great white shark seem like a guppy in comparison.
Leptocleidus This pliosaur spent most of its time in shallow ponds.
Liopleurodon With Cryptoclidus, one of the biggest of all marine reptiles.
Macroplata This aquatic reptile looked like a cross between a plesiosaur and a pliosaur.
Mauisaurus One of the few plesiosaurs to be discovered in New Zealand.
Megalneusaurus This pliosaur rivaled Liopleurodon in size.
Plesiosaurus This long-necked swimmer set the standard for aquatic reptiles.
Pliosaurus A complete skeleton if this giant swimmer was recently found in Norway.
Rhomaleosaurus One of the most fearsome predators of the Jurassic seas.
Styxosaurus This long-necked swimmer was a relative of Elasmosaurus.
Terminonatator Not quite a "Terminator," but close enough.
Thalassiodracon This impressive-sounding plesiosaur was actually very small.
Thililua Try saying its name ten times fast.
Woolungasaurus The remains of this plesiosaur were dug up in Australia.
