It’s All About the Teeth

When most people hear the word “Shark,” a sleek grey torpedo body with black eyes and large razor blade teeth is the image that comes to mind. Mainstream media and Hollywood blockbusters have done a wonderful job at painting the shark into a monster with a one track mind with a taste for human flesh- but that’s for another post! But the truth is, the majority of sharks are smaller than humans and harmless to us.

Shark Teeth
Shark Teeth Fossils [Digital Image] (n.d.). Retrieved from http://hdimagelib.com/

The shark’s jaw is comprised of several working parts that combine for the ultimate bite. The jaws are floating in the skull, but are attached by strong muscles and tendons (Skomal, 2016). This allows for the jaws to be extended and protruded downward to more effectively grab, hold and bite prey (Skomal, 2016).

bite
Broska, J. (Artist). (n.d.) Bite movement of a shark: A) resting position, B) maximal gape, C) closing of the jaws [Drawing] Retrieved from https://notendur.hi.is/

Sharks have several rows of teeth that are constantly worked and shed. The front row of teeth are called the “working” row (SharkSavers, 2017). These are the largest teeth, with each row behind progressively getting smaller. The teeth are embedded in the jaw. They are connected by soft connective tissues that allow for new teeth to shift forward and quickly replace the working tooth when it is shed, just like a conveyor belt (Skomal, 2016). Most sharks typically lose 1 tooth at a time, however some species like the cookie cutter shark (Isistius brasiliensis) will replace the entire row at a time (Parker, 2008). A shark will typically lose 20,000 teeth in a lifetime (Parker, 2008). It’s not wonder that shark teeth are the most commonly collected fossil in the world!

 Flannery, A. [Amanda Flannery] (17 July 2017). The Ultimate Guide to Sharks Shark Teeth- How Things Work 2008 [Video Clip]. Retrieved from https://www.youtube.com/

 

Sharks have a variety of diets and this means a variety of shapes and functions of teeth (SharkSavers, 2017). In nature, form follows function. Evolutionary processes have an effect on the morphology (or the way an organism looks) so that eventually features are fitted to the activities of an animal (SharkSavers, 2017). Sharks have four basic groups of types of teeth based on their corresponding feeding habits and lifestyles.

 

Benthic Feeders

Benthic feeders, or bottom feeders, are those species like the Port Jackson Shark (Heterodontus portusjacksoni) who spend their lives on the sea floor feeding on crustaceans and bivalves. Due to their diet, they have developed specialized plate-like teeth that work to crush the hard shells of their prey, like a walnut cracker (Parker, 2008). You’ll notice in the jaw of the Port Jackson that the teeth change shape further back in the mouth, moving to a wider plate shape in the back. The first part of the scientific name: Heterodontus actually means having different teeth (Hetero– different, dontus- teeth).

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Left: Port Jackson Shark [Digital Image] (n.d.). Retrieved from http://sarasotafins.weebly.com/ Right: Port Jackson Jaw [Digital Image] (n.d.). Retrieved from https://s-media-cache-ak0.pinimg.com/

Fish Feeders

Many sharks feed on fishes. Species like the Grey Nurse Shark, also known as the Sand Tiger, (Carcharias taurus) have developed long, needle-like teeth that are ideal for spearing and piercing something slippery and streamlined, like a fish (Parker, 2008; SharkSavers, 2017). While grey nurse sharks many look like your worst nightmare come reality with those fishing lure teeth, they are actually a very timid species and rarely have encounters with divers unless provoked (Skomal, 2016).

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Left: Grey Nurse Shark [Digital Image] (2012). Retrieved from http://www.sueddeutsche.de/ Center: Vevers, R. (Photographer). (2015). Tooth from a Grey Nurse Shark [Digital Image]. Retrieved from https://australianmuseum.net.au/ Right: Smith, B. J. (Author). (18 March 2016). Grey Nurse Shark Teeth [Digital Image] Retrieved from https://www.aulexic.com.au/

Mammal Feeders

Tiger sharks (Galeocerdo cuvier) are known as the garbage canes of the sea. They have a reputation of eating anything they come across, including turtles, marine mammals, fish, and even license plates (Skomal, 2016). Species that feed on marine mammals or turtles, like the tiger shark, have teeth that feature serrated edges that are ideal for piercing, cutting, and tearing away large sections of flesh away at a time (Parker, 2008). The tiger shark has a uniquely shaped tooth that features a hook and serrated arch. This acts as a two pronged attack, both stabilizing the prey by piercing in, and when the jaw swings side to side, slicing through. In effect, the tiger shark has a built in knife and fork in a single tooth.

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Left: Ryan, P. (Photographer). (n.d.). Tiger Shark [Digital Image] Retrieved from http://www.fossilguy.com/ Center: Kuhn, S. (Photographer). (25 August 2006). Tiger Shark Teeth [Digital Image] Retrieved from https://en.wikipedia.org/ Right: Skerry, B. (Photographer). (17 May, 2016). Face to Face with Tiger Shark [Digital Image]. Retrieved from http://www.epicdiving.com/

Filter Feeders

There are only 3 known species of filter feeders: The Whale shark (Rhincodon typus), Basking shark (Cetorhinus maximus), and Megamouth shark (Megachasma pelagios).  These sharks swim around with the large mouths wide open collecting tiny, microscopic organisms called plankton. But where are their teeth? In the case of the whale shark, they are incredibly tiny lining the mouth (SharkSavers, 2017). These tiny teeth are useless in feeding, but it is possible that these tiny teeth might be used in a social interactions (Frederico & Hassall, 1998). Filter feeders actually use gill rakers instead of teeth to feed. The gill rakers are specialized screens located inside the gills that catch the plankton and funnel it directly to the shark’s stomach. The water passes through the rakers and out the gills like any other shark. The rakers can actually be seen through the gill slits from behind the shark.

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Left: Feeding Whale Shark [Digital Image]. (n.d.). Retrieved from https://fthmb.tqn.com/ Center: Whale Shark Teeth [Digital Image] (n.d.). Retrieved from http://www.utilawhalesharkresearch.com/ Right: Sortino, J. (Photographer). (21 August 2010). Shark gills [Digital Image] Retrieved from https://www.flickr.com/

These four categories are very basic. Some sharks do not fit into just one category. The lined cat shark (Halaelurus lineatus) have different teeth morphology for each sex. The males have smaller teeth in the front of their jaws so they don’t harm the females when grabbing on during courtship (Frederico & Hassall, 1998). Dusky sharks (Carcharhinus obscurus), for example, combine broad cutting teeth in their upper jaws with long thin teeth in their lower jaws. This makes them ideal for catching fishes, rays, and even smaller sharks. Even the great white shark (Carcharodon carcharias) changes teeth morphology as they age. When they are young (smaller than 3 meters or so) they have narrow, needle like teeth for catching fish. They are often mistaken for mako sharks (Isurus oxyrinchus). When they reach maturity, their diet  changes towards marine mammals and their teeth change to fit that diet shift. They develop the triangular serrated teeth most people associate with the great white; these are the teeth best suited for gouging and cutting prey too large to swallow whole (Stevens, 1997).

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Left: Chapman, D. (Photographer). (29 July 2014). Juvenile Great White [Digital Image]. Retrieved from http://www.newsday.com/ Right: Skerry, B. (Photographer). (14 June 2016). Great White Shark [Digital Image] Retrieved from https://petapixel.com/

Thanks for checking out the pointy end of our sharks! Hopefully you’ve gained a little bit of insight to the live of sharks through their teeth, their habits, and ultimately their stomachs. As always, comments and discussion are more than welcome. Be sure to stop back on Friday to find out which shark or ray will be the next Featured Species. Remember you can make a difference for marine ecosystems by calling your Congress man or woman and tell them that you care about the quality of our waters! Sharks, rays, and other marine organisms cannot speak or be represented in Congress. They need your voice. Get involved and stand up for sharks.

OI000111Featured Image Source

Sand Tiger Shark [Digital Image]. (n.d.). Retrieved from http://www.discoveryuk.com/shows/shark-week/sharkopedia/a-sharks-teeth-perfectly-match-its-hunting-style/

Literature Cited

Frederico, L., & Hassall, G. (1998). Reader’s Digest Explores: Sharks. Reader’s Digest.

Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.

SharkSavers. (2017). Shark Teeth. Retrieved July 16, 2017, from http://www.sharksavers.org/en/education/biology/shark-teeth1/

Skomal, G. (2016). The Shark Handbook: The Essential Guide for Understanding the Sharks of the World. (2nd ed.). Kennebunkport, ME: Cider Mill Press.

Stevens, J. D. (1997). Sharks (6th ed.). New York: Facts on File.

 

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