the following informartion is by joshua moyer, shark biologist for use by tfui only​

SHARK TEETH

Looking at an animal’s teeth can tell you a lot about that animal’s lifestyle and evolutionary history. Shark teeth are no exception.

an endless supply of teeth
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Sharks have polyphyodont dentitions. That means their teeth are continuously grown and replaced throughout each shark’s life. Therefore, a shark never runs out of teeth. For example, some calculations suggest that a Lemon Shark (Negaprion brevirostris) may shed more than 30,000 teeth over the course of its lifespan! ​

how do sharks grow all those teeth?

The answer is found in tooth files within the jaw! Each tooth file represents a sequence of tooth development. The oldest teeth in the tooth file are the ones that stick up in functional positions. These teeth are fully formed, actively used in prey capture and processing, and can usually be seen from outside the mouth. Behind the functional teeth there are replacement teeth. The oldest replacement teeth are usually fully formed and ready to move forward in the tooth file to the take a functional position. Other replacement teeth are still developing. As the tooth develops, tissues inside the teeth mineralize and harden. ​

WHAT ARE SHARK TEETH MADE OF?

BASIC ANATOMY

If you look at a shark tooth, it isn’t difficult to discern the crown from the root. In humans, tooth roots sit in sockets within the jaw, but sharks have lyodont teeth. That means that they are not anchored to the jaw. Rather teeth are found in connective tissue that covers the jaw. Shark teeth have a root made of a type of dentine called osteodentine.​

A BIGGER BITE

The crown of a shark tooth, which could also be considered the “business end” of the tooth, is covered by enameloid. It is called enameloid and not enamel because the enameloid of shark teeth have an additional element in them – fluorine. Another difference between the enameloid of shark teeth and the enamel of human teeth is that when a shark makes a tooth, the enameloid of the crown is the first part of the tooth that is made. In humans, enamel is one of the last tissues deposited on a developing tooth. Check out the CT reconstruction of a Great White’s tooth file, and you’ll see that very young teeth in the back are little more than hollow enameloid crowns. ​

Picture: Ian Waldie  /  Getty Images file

SINK YOUR TEETH INTO MORE...

Underneath the enameloid in the teeth of many sharks, like the Blue Shark (Prionace glauca) or the Tiger Shark (Galeocerdo cuvier), there is tissue called orthodentine. It surrounds a pulp cavity inside the tooth. In other sharks, like the Great White (Carcharodon carcharias) or Mako (Isurus oxyrinchus) sharks, there is no hollow pulp cavity in fully developed teeth. Instead, the crown is filled with osteodentine, the same tissue that makes the root.​

Artwork by dswatercolors (David Scheirer).

form and function

Shark teeth come in an amazing variety of forms or morphologies. Tooth  morphology gives shark biologists clues to what a shark eats. For example, a long, pointy tooth may function like the tines of a fork. This is a common tooth shape in sharks that eat fast-moving or slippery prey and must hold on to the prey once they catch it. A good example of this tooth shape is the tooth of a Mako shark.

Other sharks have more triangular and serrated teeth that are often used for cutting or sawing through prey. A classic example of this tooth morphology is the tooth of a Great White. Adult Great Whites put their serrated teeth to good use cutting through the meat of marine mammals, fishes, and even other sharks, but perhaps the most heavily serrated teeth belong to the Tiger Shark. Tiger Sharks have serrations on top of other serrations, and the entire tooth is shaped like a can opener! This makes the Tiger Shark well equipped for sawing through the hard shell of seas turtles or even taking advantage of an easy meal, like dead whales or carrion that has washed out to sea.
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do the teeth on the two jaws differ?

​Many sharks have teeth with different morphologies in the upper jaw, or palatoquadrate, and in the lower jaw, or Meckel’s cartilage. For example, Blue Sharks, Snaggletooth Sharks, Bull Sharks, and a variety of other species have more slender teeth on the lower jaw and more broad, serrated teeth on the upper jaw. This is sometimes called a “knife and fork” dentition after the putative function of each tooth’s morphology. This arrangement of differently shaped teeth on the upper and lower jaws is called dignathic (two jaws) heterodonty (different teeth).

​Sharks belong to the class of fishes called Chondrichthyes, meaning they have a skeleton made of cartilage and not bone. Cartilage does not fossilize well. 

toothy fossils

Teeth and the very similar but often much smaller placoid scales of sharks, on the other hand, fossilize very well! By the time the Devonian Period started a little more than 400 million years ago, sharks had evolved polyphyodont dentitions and were growing, shedding, and replacing teeth. That’s good news for paleontologists trying to piece together the evolutionary histories and diversity of sharks and other fishes.

​Why are all those teeth important? Because shark teeth fossilize so well and there are so many of them in the fossil record, they are one of the most commonly collected fossils in the world, and they have been found in some surprising places. For example, teeth from members of the extinct mackerel shark genus Otodus have been unearthed in the mountains of Morocco, high above sea level. This is one piece of evidence that Earth’s landscapes have changed dramatically over the course of evolutionary time. Fossilized teeth of other species of extinct sharks are found on every continent. Shark teeth have even been recovered from portions of Antarctica! By looking at the similarities between fossilized shark teeth and the teeth of modern, or extant (the opposite of extinct), sharks researchers can make inferences about the evolutionary lineage and ecology of a long-gone shark species.

For example, when you look at the teeth of Carcharocles megalodon, it isn’t difficult to see the similarities between those teeth and the teeth of a modern Great White. Thanks to what were know about the relationships between the form and function of shark teeth, we can infer that C. megalodon was likely a large, predatory shark. However, there are some subtle differences that let researchers know that C. megalodon was not just a really big version of the Great White. Thanks to scientists’ abilities to “read” the morphology of shark teeth, we can learn things about sharks that disappeared long before the first human ever saw the light of day!