Ichthyosaurus: Prehistoric Animal of the Week

This week we shall be looking at a reptile that once called the oceans over what is now Ireland, in addition to a lot of other places, home.  Enter Ichthyosaurus!  Ichthyosaurus was a genus of marine reptile that lived during the early Jurassic, about 190 million years ago, in the oceans that covered much of Europe at the time.  Many good Icthyosaurus remains have been found in Germany, Belgium, Switzerland, and England.  A few have also been found in Ireland!  This animal measured only about six feet long from snout to tail and its diet consisted of fish and cephalopods.  The genus, Itchthyosaurus, translates to "fish lizard" and includes several species.

Ichthyosaurus communis life reconstruction by Christopher DiPiazza

The first Ichthyosaurus fossils were discovered by a twelve-year old girl named Mary Anning during the early 19th century in England along with many other important Jurassic marine fossils.  We know a lot about Ichthyosaurus thanks to a myriad of well-preserved remains of it and its close relatives that have been unearthed since then over the years.  We know that Ichthyosaurus would have had a dorsal flipper and vertical tail fluke, much like a fish, thanks to some fossils that preserved a soft-tissue outline of the dead animal.  We also know, thanks to the remains of a closely related ichthyosaur, that these animals gave birth to live young rather than laying eggs like most reptiles do.  Scientists used to assume that all prehistoric marine reptiles would have hauled out on land to lay eggs like sea turtles do prior to this discovery.  We also know what they ate belemnite (squid-like cephalopod) and fish thanks to remains found in Ichthyosaurus stomach cavities and coprolites. (fossilized poop)

Ichthyosaurus communis skeleton.

Ichthyosaurus was very similar looking to fish and modern dolphins.  This is yet another excellent example of convergent evolution- unrelated animals evolving similar body plans and adaptations to suit similar lifestyles.  Because of this we know Ichthyosaurus was likely a very fast swimmer.  Unlike fish, however, Ichthyosaurus would have needed to come to the water's surface to breathe air since it was a reptile with lungs.  The eye sockets on Ichthyosaurus were very large so this animal likely had superb vision, especially in the dark.  This could mean that Ichthyosaurus was either mostly active at night, and/or it was able to hunt in lower depths where it was dark.  In some specimens, the skulls even preserved scleral rings, which are bony rings inside the sockets that supported the large eyes.  Similar to some dolphins, it also had a long, skinny snout lined with many cone-shaped teeth for catching swift-swimming prey. 

That's all for this week!  Hope you enjoyed our St. Patrick's Day Irish (and the rest of Europe pretty much) creature!  If you want to see me review and paint a particular beast feel free to comment below or on our facebook page.  Also special thanks to Dr. Adam Stuart Smith for helping me out with this post!

Works Cited

Martill D.M. 1993. Soupy Substrates: A Medium for the Exceptional Preservation of Ichthyosaurs of the Posidonia Shale (Lower Jurassic) of Germany. Kaupia - Darmstädter Beiträge zur Naturgeschichte 2: 77-97

Smith, Adam S. "Rare Ichthyosaur and Plesiosaur Material from the Lower Jurassic of Ireland." Irish Journal of Earth Sciences 28 (2010): 47-52. Web.