Orthacanthus: Prehistoric Animal of the Week

Shark week is over so lets say farewell to every nerd's favorite week of summer by checking out a truly fascinating-looking prehistoric shark.  Enter Orthacanthus!  This shark actually lived in fresh water swamps throughout what is now the Northern Hemisphere as far back as the Devonian (400 million years ago) through the end of the Permian Era (260 million years ago).  There are a few species within the genus, Orthacanthus, but they are all relatively similar to one another.  The fact that a genus of animal can last 140 million years is impressive but then again sharks are known for that sort of thing.  Orthacanthus grew to about ten feet long and belongs to the family of sharks called Xenacanths that was prevalent during this long time span.

Orthacanthus senckenbergianus life reconstruction by Christopher DiPiazza.

Orthacanthus doesn't really look like many sharks alive today.  Its body was much longer and more slender and it had a shallow, rounded dorsal fin running from the back of its head all the way down to the base of its tail instead of the famous triangle fin we commonly associate with sharks.  These physical characteristics gave it the appearance of an eel more than anything else but it was a true shark nonetheless.  It also sported a long spike growing up from the base of its skull which may have been a defensive weapon against larger predators.  It is this spike that gives the shark its name which translates to "Vertical Spike".  There are actually several kinds of living sharks that have spikes, too but all of theirs grow from the base of the dorsal fin, not the skull. Orthacanthus's teeth grew in pairs or "twins".  This means that there were two pointy teeth coming out of one root.

Orthacanthus fossil.

When alive Orthacanthus likely was an opportunistic predator and probably hunted the many kinds of other fish as well as amphibians it shared its shallow freshwater environment with.  It may also have periodically encountered the giant mammal-like reptile, Dimetrodon, which could have preyed upon it.

Orthacanthus tooth that shows the twin...wait no sorry this one has three.  The triplet style tooth.  Sharks always go above and beyond when it comes to teeth evolution.

That's all for this week!  Remember, just because Shark Week is done doesn't mean you can't still be shark crazy the rest of the year!  As always feel free to comment below and on facebook!

References

D. Heyler and C. Poplin. 1989. Systematics and relationships among the Xenacanthiformes (Pisces, Chondrichthyes) in the light of Carboniferous and Permian French materal. Acta Musei Reginaehradecensis S. A.: Scientiae Naturales 22:69-78