Shark Teeth: Dentist Approved

​Did you know that sharks don’t get cavities? 

Tooth Replacement
Did you know that sharks don’t get cavities? Most elasmobranchs pass their yearly dental checkups with flying colors because they are constantly replacing their teeth, with many species capable of shedding 30,000 or more in their lifetime (1). Sharks are polyphylodonts, meaning they have multiple rows of teeth at once; new ones are always forming to replace the old that have helped catch prey and endure the elements (2). You may imagine a never-ending conveyor belt of teeth. New teeth emerge from the back and migrate forward as old teeth fall out towards the front. All species shed teeth at different rates, but all benefit by a fresh set of pearly “great” whites.

Specialization
It is difficult to make generalizations about shark teeth because there is extreme diversity amongst the elasmobranchs. Dentition has evolved to accommodate different food types, climates, and environments (3). Various species may have incredibly different teeth. As an example, let us examine three species of shark that all have quite diverse feeding habits and unique teeth: the nurse shark (Ginglymostoma cirratum), the shortfin mako (Isurus oxyrinchus), and the white shark (Carcharodon carcharias).
​

• Nurse sharks live on the bottom or in a coral reef, preying on small benthic animals like fish and mollusks. Nurse sharks tend to be ‘lazy’ (and energetically efficient) so they will corner or surprise a fish and use suction to deliver it into the mouth4. The teeth are small and uninvolved in catching or tearing the prey, but used for crushing bivalves or biting down to assure that a fish won’t escape.
  ​

Picture credit: http://www.fossilsonline.com/index.php?main_page=product_info&products_id=270

• The mako shark uses a similar grasping technique, as they hunt with teeth that protrude out of the mouth and face inward. These pelagic sharks’ teeth are used to quickly snag fish out of the deep blue, assuring that once a fish is caught, it is only going straight into the mouth. 
  ​

• Great white sharks are found in coastal and deep water, so they tend to eat large prey like big fish, pinnipeds, or carrion. They capture with force and bite into their meal, using the serrated edges of their teeth like knives to bite out chunks.
  ​

​​You can absolutely judge a shark by its teeth... you can infer what species a shark is by its tooth, how and what it eats, and where it tends to dwell. To complicate things… one shark can have differently shaped teeth on its top jaw than it does on the bottom or different ones in the middle than it has on the sides. Factors like age and sex can show some structural differences within a species. Shark teeth can be categorized as such: crushing teeth (like the nurse shark), grasping teeth (like the mako), and cutting teeth (like the great white). However, there are some that hardly fit into a category at all. Whale sharks and basking sharks are filter feeders with nonfunctional teeth, eagle rays have ‘plates’ in place of teeth for mollusk crushing, the cookie cutter sharks suck onto large fish and dig in sharp hole-punching jaws while slowly eating away at a host- and the list of examples goes on. There is a LOT to learn about a shark from the characteristics of its teeth. When you find a shark tooth on the beach, you might be able to learn a little about that shark’s life.  
​

Bonus: Judge a Shark by its Fossil
As a shark tooth hunter myself, I am lucky to live near the Shark Tooth Capital of the World! This is Venice, Florida, where especially after a storm, you can find plenty of those beloved little black triangles on a casual stroll down the beach, or possibly a megalodon tooth on a scuba dive. Sharks teeth are white when the shark is alive, but the fossils we find are thousands of years old and become black due to nutrient absorption. Teeth fall to the ocean floor and are covered in sediment that protects and seals them off from oxygen and bacteria that would otherwise cause damage. Water seeps through the sediment and carries minerals from the surrounding area that are deposited into the porous teeth (a process known as permineralization (6). This is why some fossilized teeth are light or dark brown, reddish, tan, or black; they become the color of the sediment in which it was fossilized. These fossils are a great footprint that we have from extinct, extant, and evolved shark species. 
​

Photo by Valerie Hagan. Various shapes, sizes, colors, and conditions of shark teeth fossils found in the Venice, FL area.

GLOSSARY

• Polyphylodont- an animals whose teeth are constantly replaced
• Dentition- the arrangement of teeth
• Benthic- bottom dwelling
• Pelagic- open sea dwelling
• Pinnipeds- aquatic mammals like seals, sea lions, walrus
• Carrion- dead and decaying animals
• Sexual dimorphism- difference in a characteristic between male and female of a same species
• Megalodon- extinct species of shark, likened to a great white that reached 50 feet in length
• Sediment- dirt and compounds that settle on the bottom
• Permineralization- a process of fossilization where minerals are absorbed from surroundings
• Extinct- a species that once existed but is no longer around
• Extant- a species that currently exists

References

1. https://www.zmescience.com/other/science-abc/sink-teeth-cool-facts-sharks/
2. Liam, R. Martin, K. Cooper, R. Metscher, B. Underwood, C. Fraser, G. “An ancient dental gene set governs development and continuous regeneration of teeth in sharks.” Developmental Biology.Vol 415, Issue 2. 15 July 2016. Pg 347-370. https://www.sciencedirect.com/science/article/pii/S0012160616300483?via%3Dihub
3. http://www.naturalhistorymag.com/biomechanics/172103/when-the-shark-bites
4. https://www.sciencedaily.com/releases/2016/02/160201220322.htm
5. http://www.fossilguy.com/gallery/vert/fish-shark/remnant.htm
6. https://www.floridamuseum.ufl.edu/fish/discover/sharks/fossil-sharks/fossil-vs-modern/

GUEST BLOGGER AND TFUI OFFICER valerie hagan

Hello! I’m Valerie Hagan, a biologist at Mote Marine Laboratory in Sarasota, FL. My favorite places to be are on the beach, in my kayak, or on a scuba dive where I’m always searching the water for fins (or teeth!). I believe we tend to be scared of what we do not understand, so I’m here to help us understand sharks.