Plesiosaurus: Prehisroric Animal of the Week

This week we will be looking at a creature with a very well known and recognized name, but maybe not well-understood for what it really was.  Check out Plesiosaurus dolichodeirus!

Plesiosaurus swam in the ocean over what is now Dorset, England during the early Jurassic, between about 198 and 175 million years ago.  Its shape is iconic, and recognized by the general public, with its small head on the tip of a long neck, wide, almost turtle-shaped body, and four flippers instead of feet, which it used to propel itself through the water.  Plesiosaurus and its relatives, the other plesiosaurs, were not dinosaurs, but a separate kind of now-extinct reptile that evolved independently during the Mesozoic.  When alive, Plesiosaurus would have eaten meat in the form of fish, mollusks, or any other small sea creature it could catch.  It would have shared its habitat with its fellow marine reptile, Ichthyosaurus.  From snout to tail, an adult Plesiosaurus measured about eleven feet long. The genus name, Plesiosaurus, translates to "near reptile/lizard".

Life reconstruction of Plesiosaurus dolichodeirus, by Christopher DiPiazza.

Plesiosaurus's skull was somewhat flattened with its eyes facing upwards.  It had many long, pointed teeth, which in addition to looking pretty scary up close, evolved for better catching and holding onto small, slippery prey, like a cage.  When Plesiosaurus' mouth was closed, these teeth would have likely still been visible outside the mouth and interlocked.

Plesiosaurus dolichodeirus skull at the Museum of Natural History in London.

The neck of Plesiosaurus was very long and consisted of up to forty two vertebrae.  The long-necked plesiosaurs have been commonly depicted in artwork and pop culture as swimming with their heads above the water in a perfect S shape, almost like that of a swan.  In real life, however, this was physically impossible.  Real plesiosaurs would have been able to bend their necks up and down to some degree, but not in that iconic Loch Ness Monster pose.  (one of the many reasons why it is impossible for there to be a real plesiosaur living in there today)  They could, however, have moved their necks around from side to side fairly well.  the reason for this long neck is the subject of a lot of debate for paleontologists.  One hypothesis is that the long neck was a tool to help the animal reach into narrow spaces where fish and other prey may have been hiding, like between rocks and coral.  Another idea is that the neck was a good way to distance the large body from the unsuspecting prey.

"Don't mind me, guys.  I'm nothing but a harmless little fish, like you.  Totally not a carnivorous reptile with a giant body attached to the back..."

 
Plesiosaurus' body, like all of the members of its family, was not flexible at all.  It would have been similar to that of a sea turtle, actually.  Like turtles, plesiosaurs would have relied on their long flippers to power them through the water.  They were likely not fast swimmers compared to their contemporaries, the ichthyosaurs.

Plesiosaurus dolichodeirus full skeleton originally found by Mary Anning on display at the London Museum of Natural History.

Plesiosaurus was another one of the well known prehistoric animals that was originally found by famed fossil hunter, Mary Anning, back in the 1800s.  Since then, many specimens of long-necked, flippered reptiles have been named Plesiosaurus but further, recent research has found out that many of these fossils were actually deserving of their own names.  Today, there is only one valid species, Plesiosaurus dolichodierus, and its type specimen is the original fossil that started it all.

Plesiosaurus pencil illustration by Adam Stuart Smith.

That is all for this week!  Special thanks to my friend, and plesiosaur expert, Dr. Adam Stuart Smith!  For more first-hand plesiosaur information be sure to check out his website.  As always comment below or on our facebook page!  

References

Andrews, C. W. 1896. "On the structure of the plesiosaurian skull". Quarterly Journal of the Geological Society, London, 52, 246-253.

Brown, D. S. 1981. "The English Upper Jurassic Plesiosauroidea (Reptilia) and a review of the phylogeny and classification of the Plesiosauria". Bulletin of the British Museum (Natural History): Geology, 35, (4), 253-347.

Storrs, G. W. 1997. "Morphological and taxonomic clarification of the genus Plesiosaurus". 145-190. In Callaway, J. M and Nicholls, E. L. (eds.). Ancient Marine Reptiles. Academic press. London.

Torrens, Hugh 1995. "Mary Anning (1799–1847) of Lyme; 'The Greatest Fossilist the World Ever Knew'". The British Journal for the History of Science, 25 (3): 257–284