Cladoselache: Prehistoric Beast of the Week

Get your diving gear ready...and time machines too I guess.  We are about to check out another awesome prehistoric shark!  Say hello to Cladoselache!  Cladoselache was a genus of shark that included several species, but the most well understood is called Cladoselache fyleri.  It lived during the late Devonian period, about 375 million years ago.  (much older than the first dinosaurs) It swam in oceans that once covered what is now North America, the best preserved specimens of this ancient fish being from Ohio.  Cladoselache could grow to be about six feet long from snout to tail and would have eaten meat (like all sharks) in life.  The genus name translates to "Branch Tooth Shark" due to the fact that could have multiple teeth per root.

Life reconstruction of Cladoselache fyleri, by Christopher DiPiazza

Cladoselache was a very interesting animal due to the fact that, despite being so old, it had some characteristics about it that are still very prominent in sharks today.  At the same time it also had some features that are completely alien by living shark standards.  The mouth of this shark was at the very front of the snout, called a terminal mouth.  This is in contrast to the kinds of mouths that you see in many modern sharks, like great whites for instance, that have that long nose jutting out before their actual mouths. (which is called subterminal)  However, some sharks today also exhibit the terminal mouth, like the weirdly wonderful Frilled Shark, for instance.  Inside the mouth Cladoselache had many long pointed teeth, that could branch out from a single root.  The teeth weren't serrated, suggesting it didn't tear apart its prey, but rather would have hooked it and sucked it completely into its jaws whole.  In fact, some very well-preserved specimens of Cladoselache even show whole fish skeletons in the stomach cavity.  Thanks to these we even can tell that Cladoselache grabbed and swallowed its prey tail-first!  Cladoselache fyleri also had seven gill slits on each side of its head, which is more than most sharks today, but also not unheard of by modern shark standards either.

Cladoselache tooth.  Note the multiple points.

One feature about Cladoselache that you won't find in any modern sharks is the fact that it was almost devoid of any toothy scales, called denticles, that sharks are so well known for being covered in.  In fact, this shark was almost completely naked, scale-wise, except for a few regions around the face and on its fins.  Paleontologists still have no clue why this was.  It also had short spines in front of its two dorsal (back) fins which may have helped it cut the water as it swam.

Cladoselache fyleri fossil on display at the American Museum of Natural History in New York.

Thanks to beautifully preserves specimens of Cladoselache, we even know what the outline of its body looked like.  This is rare since shark skeletons are almost completely composed of soft cartilage, not bone, and therefore rarely fossilize.  Most other kinds of prehistoric sharks are only known from teeth.  Not the case with Cladoselache, though.  It had a long, streamlined body and its tail was an almost perfectly symmetrical crescent shape with pronounced keels on the sides for tail muscles.  When you compare this to the tails of sharks and other fish today, you will see that symmetrical shape is present in extremely fast-swimming creatures like Mako Sharks and Tuna.  It is likely Cladoselache was fast, too, using its speed to grab prey and also escape predators, like the twenty-foot long, armored fish, Dunkleosteus.

That is all for this week!  As always please comment below on the facebook page!

References

"Ancient Sharks." Ancient Sharks. Reequest Center for Shark Research N.p., n.d. Web. 04 July 2016. 

A. S. Woodward & E. J. White, The dermal tubercles of the Upper Devonian shark Cladosclache. - Annals and Magazine of Natural History 11: 367–368. - 1938.

B. Dean, Contributions to the morphology of Cladoselache (Cladodus). Journal of Morphology 9:87–114. - 1894.