Shocking Shark Teeth

One of the key points of the previous posting is that if you find a hollow tooth in good condition but missing a root, it is possible that you have found part of a shark dentition.  You should carefully check the area to see if you find more teeth from the same animal.  If so this would be a site of dead shark as this is the only way that unerupted replacement teeth are lost.  A shark dentition is a scientifically important find and a professional should be contacted to remove and study it.

The Pacific equivalent of the Caribbean Reef Shark is the Grey Reef Shark, Carcharhinus amblyrhynchos.  Unlike the Caribbean Reef Shark, this shark is less tolerant of divers closely approaching it and can react violently.  While I have no fossils of this species, it would surprise me if it didn’t turn up in tropical Pacific marine fossil sites.  From the closeups of the upper jaw, note that one file of teeth is missing.  The adjacent tooth’s shoulder has become elongated, partially filling in the gap.  This leads conveniently into my next subjects, tooth replacement in sharks and pathologic teeth.

Next up is the Silky Shark, Carcharhinus falciformis.  The jaws of this shark are commonly found in shell shops as this is a schooling shark targeted by criminal shark finners.  Teeth from this shark are commonly found as fossils. The teeth are medium sized.  Upper teeth from this shark are fairly easy to identify.  Lower teeth again are undistinguished.  The upper teeth are angular with a inclined blade (except for the very anterior teeth).  Viewing the teeth from the labial side (outside, flat side), there are very distinctive notches where the coarser serrations of the shoulders meet the finer serrations of the main cusp.   The last image is a pathologic tooth where teeth from two adjacent files are merged together.  We will discuss pathologic teeth in an upcoming post. 

An interesting Miocene species is the Copper Shark, Carcharhinus brachyurus.  This shark is a common find in Atlantic Miocene deposits, however it no longer exists in the Atlantic.  The closest it is now found is the Pacific coast of Mexico.  In the future, we will discuss additional species which are also no longer found in the Atlantic Ocean.  The teeth are curved, fairly narrow and have wide roots.  The jaw illustrated has a stingray barb embedded inside it.

Another very common Miocene and later species is the Caribbean Reef Shark, Carcharhinus perezii.  Also known in the fossil record as C. egertoni.  The problem with C. egertoni is that it has been a dumping ground for multiple fossil species.  One of the problems with the genus Carcharhinus is that many of the species have similar appearing teeth so they get lumped together such as the common practice of calling a random Carcharhinus tooth a bull shark tooth.  This species is common in the Caribbean area and in some places it is used for shark dives as it is not usually an aggressive species and adapts to the presence of divers and free handouts.  In most of the movies where you see the swimmers ominously surrounded by sharks, these are almost always Caribbean reef sharks.  Upper teeth are somewhat inclined and coarsely serrated with coarser serrations on the enamel shoulders.  Again lower teeth are erect and fairly undistinguished. 

Now to the other common blacktip shark, Carcharhinus limbatus.  This shark migrates up and down the Atlantic coast of Florida in huge schools.  It can be seen in large numbers swimming among bathers in the shallow waters just off the beach.  It is responsible for a large number of the shark attacks on the Florida east coast (shark attack capital of the world).  These are cases of mistaken identity when the shark sees a flash of skin or jewelry in murky water and bites thinking that it is a fish.  This shark has thin, dagger like teeth and typically leaves small puncture wounds unlike the major damage inflicted by a bull or tiger shark.  Recently some other species have been split off this species due to DNA analysis and I suspect more will be.  The teeth of these new species are similar and basically indistinguishable from limbatus.  Upper teeth are erect or slightly inclined and have fine serrations on the blade with coarser serrations on the shoulders.  Lower teeth are narrow, erect and have very fine serrations distinguishable usually only with magnification.

Back to the Genus Carcharhinus.  The next shark(s) we will discuss are the blacktip sharks.  Until fairly recently there were considered to be two species of blacktip sharks.  The Blacktip Shark, Carcharhinus limbatus and the Reef Blacktip Shark, Carcharhinus melanopterus.  In actuality there are several species of Carcharhinids with black tipped fins.  Many of these species are common named species, others are rare and confined to local areas.  Also new species are being separated out by DNA.  Rather than discussing the common named species or the limited range species, I will focus on the two named above.  The Reef Blacktip shark is found in tropical, shallow West Pacific and Indian Ocean waters.  As such it, it is virtually unknown as fossils but could be collected by persons in those areas.  The upper teeth have large serrations on the shoulders and extremely fine serrations on the main cusp (blade).  Lower teeth are the typical undistinguished Carcharhinid type.  It is has attractive markings and is very hardy and thus a common shark in public and some large private aquariums.  The Pondicherry shark (Carcharhinus hemiodon) which was believed to be extinct until rediscovered this year (2019) has similar teeth.