Shark jaws

October 23, 2010 • 5:50 am

Here are two more photos from my immensely edifying visit to Jim Krupa’s lab at The University of Kentucky.  They show the extreme diversity of morphology that evolution can produce in a single group.

The first shows the jaw of what I remember as a tiger shark, Galeocerdo cuvier.  National Geographic notes that “They have sharp, highly serrated teeth and powerful jaws that allow them to crack the shells of sea turtles and clams. The stomach contents of captured tiger sharks have included stingrays, sea snakes, seals, birds, squids, and even license plates and old tires.”

The rows of teeth are lined up, waiting in the wings, to be replaced after one on duty is lost. The teeth aren’t embedded in the jaw, but merely in the gum tissue.  Wikipedia has a good article on them.

Sharks are in the class Chondrichthyes:  they have cartilage rather than bone.  The subclass Elasmobranchii includes sharks, skates and rays.  And the tiger shark is in the largest order of elasmobranchs, the Carcharhiniformes.

And here’s one of the weirdest elasmobranchs—the jaw of the Port Jackson shark (Heterodontus portusjacksoni), endemic to Australian waters.  It’s in the order Heterodontiformes (“bull sharks”), distinguished, among other things, by having the mouth completely in front of the eyes. The “Heterodontus” part of the genus name means “different teeth,” and that’s indeed what you see, spectacularly, in the jaw.  Having differentiated teeth in the jaw is very rare in sharks:

The small teeth in front are for grabbing and piercing, the ones at the rear for grinding up stuff, especially molluscs.  The Florida Museum of Natural History site notes:

This species feeds primarily on echinoderms, crustaceans, molluscs, and some small fish. Sea urchins and large gastropod molluscs are noted in almost every study on the diets of Port Jackson sharks. Stomach contents are typically ground up too small for full identification, thus leading researchers to believe Port Jackson sharks grind their food thoroughly before swallowing. This is also supported with juvenile diets, since it has been noted that juveniles eat more soft-bodied animals, and contain less molar-like teeth.

Here’s what the jaws look like in situ:

For $750 you can actually buy a Port Jackson shark for your aquarium, but I’m not sure why anyone would do that, as they grow over five feet long.

You can see the variety of sharks’ teeth here, and if you’re into buying recent or fossil teeth, here’s a place to start,

12 thoughts on “Shark jaws

  1. Awesome photos.

    Am I misreading things or are you implying that Heterodontus is a chimaera? I am pretty sure that Heterodontus is a galeomorph – well-within crown sharks (selachians), although it is vaguely convergent on chimaeras in some respects.

    The ‘dentition’ of true Holocephalians is even weirder, composed of mineralized pads that are fused to the jaws.

    1. Oh dear, I screwed that one up. The Port Jackson shark is clearly an elasmobranch, and I don’t know how I got it wrong.

      Thank God some of my readers know biology!

      I’ve fixed the entry; thanks for your correction.

  2. For $750 you can actually buy a Port Jackson shark for your aquarium, but I’m not sure why anyone would do that, as they grow over five feet long.

    What? You don’t have 50 m aquariums in your livingroom?

  3. BTW, what on earth are those portholes on the upper “lip” of the PJ shark?

    Also, in the middle shot, what are the two skulls in the background? L = ?? R = walrus?

  4. Wow, just amazed by the PJ shark! So glad you included the in situ view, as I was having a hard time visualizing it from the jaw pic.

    ‘Twould be cool to have a tank big enough for a shark like that, but I’d hate to feed it, inverts being some of my fav SW tank denizens…

  5. Is there any good evo-devo account of the shape of the tiger shark’s teeth? And tooth shape generally in the Carchariniformes?

    The triangle shapes of Carcharodon and the slender teeth of the mako sharks are easily relatable, and make sense as adaptations to cutting meat or blubber and catching fish, respectively. But the toth shape of Galeocerdo has always intrigued me.

  6. More evidence for evolution. I believe that is the hairy hand of Australopithecus holding the Port Jackson shark jaw.

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