Edestus: Beast of the Week

As this year's shark week comes to a close, let's take a look at an ancient fish that makes even the modern Great White look relatively mundane.  Check out Edestus!  Most people are aware that sharks have been around since prehistoric times, even before the first dinosaurs, but many don't realize how different some of these fish looked from any that are alive today. 

Edestus was a genus of of prehistoric cartilaginous fish (fish with a skeleton mostly made of cartilage, like rays, ratfish, and sharks) that lived during the late Carboniferous Peridd, about 300 million years ago in oceans around the world.  The genus, Edestus, includes several species, the largest of which, called Edestus giganteus, is estimated to have been about twenty feet long from snout to tail when alive.  The genus name, Edestus, translates to "Devourer" because the teeth...well, you'll see why.

Edestus heinrichi life reconstruction by Christopher DiPiazza.  Since only the jaws are known, the body I used references from modern sharks, and chimera fish.  The real living animal may have looked different from this.

Edestus had some of the most unique jaws of any vertebrate, let alone fish.  Unlike most sharks, which constantly replace their teeth during their lives as they fall out for various reasons, Edestus held on to its teeth, but also added teeth as it grew.  As this happened the upper and lower jaws of Edestus were gradually growing and curving outwards as the animal aged, making room for new teeth.  This resulted in a profile that looks a lot like when you stick two Pringles chips in your mouth and pretend to be a duck.  (If you ever ate Pringles in your life, you have done this.)

"Look at me!  I'm an Edestus!"

The teeth themselves varied a bit from species to species of Edestus, but they all appear to have been meant for eating meat.  Another interesting thing about the teeth is the fact that they were symmetrical, so one side wasn't more flat than the other.  This means that Edestus' mouth consisted of a single row of teeth, which were parallel to the body, rather than perpendicular like in other animals.  Think of it sort of like having a pair of scissors sticking out of the front of the face.

Photograph of three different species of Edestus teeth from Itano's 2014 paper.  The species pictured from top to bottom are E. heinrichi, E. minor, and E. newtoni.

So what kind of feeding strategy did Edestus employ with this truly unique mouth?  One idea is that it would have swam through its prey, essentially cutting it in half as it did so, and then swallowed the pieces after.  Another idea is that it was adapted for cracking open prey with tough shells on the outside, like marine arthropods.  Some believe it was a jellyfish eater. 

That is all for this week!  As always feel free to comment below or on our facebook page!

References

Itano, W. 2015. An abraded tooth of Edestus (Chondrichthyes, Eugeneodontiformes): Evidence for a unique mode of predation. Transactions of the Kansas Academy of Science. 118 (1-2): 1-9

Itano, W. 2014. Edestus, the strangest shark? First report from New Mexico, North American Paleobiogeography, and a new hypothesis on its method of predation. The Mountain Geologist. 51 (3): 201-221