Shark TeethMsC Marine Biology
Have you been lucky enough to have found a shark tooth embedded in the sand at the beach or in a river somewhere close to the coast? How cool! Did you know that looking at a shark’s tooth can tell you a lot about its lifestyle and evolutionary history? Here is what scientists know about shark teeth…
Shark teeth vs. human teeth
As you probably guessed, humans and sharks do not have the same number of teeth. As humans, we lose our baby teeth when we are little and then get a set of permanent ‘adult’ teeth that are meant to last us our entire lives. That means you have to be careful with them! Sharks, on the other hand, have teeth that fall out all the time and are continuously replaced with new teeth.
How many teeth does a shark go through in its lifetime? Well, that answer depends on the species. For example, calculations suggest that a lemon shark may shed more than 30,000 teeth over the course of its lifespan! On average, a shark can lose at least one of its teeth every week since they are not attached to gums like ours are.
How many rows of teeth do the sharks actually use?
Sharks can have multiple rows that are attached to the jaws by connective tissue, but they usually only use the first couple. The other rows are folded back against the inside of the jaw, where they are quickly forming. When one tooth pops off, the one in the row behind it moves up to take its place; lost teeth can sometimes be replaced in as little as 24 hours.
Fun fact: the cookiecutter shark doesn’t just lose one tooth – it sheds its entire lower plate of teeth all at once, often swallowing it with whatever it is eating!
Are all the teeth in a shark’s mouth the same shape?
Nope! Many sharks have teeth with shapes that are different in the upper jaw and in the lower jaw. For example, a bull shark’s teeth in the upper jaw are broad, triangular and heavily serrated, whereas its teeth in the lower jaw have a broad base but are narrow and triangular with fine serrations. Having more than one type of tooth shape within the same fish is called ‘dignathic heterodonty’.
What are shark teeth made out of?
The outer part of a shark’s tooth is made up of hard and mineral-rich enameloid – in fact, enameloid is one of the hardest mineralised tissues developed by animals. In reptiles and mammals (including humans), this outermost layer of the tooth is known as enamel.
Enameloid differs from typical enamel in its chemistry and its developmental timing (it is made first instead of last, as it is in humans). Similar to a human tooth, a shark’s tooth has a core made of dentine. Depending on the structure of the dentine, scientists distinguish between two different types: orthodentine and osteodentine. Species like the tiger shark have orthodentine surrounding a pulpy cavity. It is quite compact and is similar to the dentine we can find in human teeth. Other sharks, like the great white, lack that cavity and their teeth instead have osteodentine, which is spongy in appearance and kind of resembles real bone!
Can sharks get cavities?
Sharks do not get cavities because the surface of their teeth contains fluoride. That is the same active ingredient found in a lot of toothpastes and mouthwashes!
So why all the different shapes?
There are more than 500 different species of sharks roaming our oceans today and each one has its own distinctively shaped teeth (although many look quite similar), depending on what they eat! Tooth morphology gives shark biologists clues to what a shark eats. The teeth are classified by researchers by what they do, such as tearing or grinding. Here is a further breakdown:
One of the most famous types of shark, the great white, has pointed lower teeth and triangular upper teeth. These serrated chompers are useful for cutting up large prey – such as whales, dolphins and large seals – into smaller pieces so the shark can swallow it. Sharks don’t chew! An extreme sawing action can be seen in tiger sharks, where their teeth are specially adapted to sawing through tough surfaces, like turtle shells.
A long, pointy tooth is similar to the tines of a fork. This is a common tooth shape in sharks that need to grasp fast-moving or slippery meals such as stingrays, squid and fish. A good example of this tooth shape is the needle-like teeth of the tassled wobbegong.
Some shark species have dense, flattened teeth that are used mainly for grinding and crushing their prey, which is usually something with a shell (such as crustaceans and bivalves). The flat teeth help crack open the shell and let the shark get to the good stuff inside! Sharks with teeth like this include the bowmouth guitarshark, which tends to spend its time at the bottom of the ocean floor where its food usually is.
Long, hooked teeth are similar to needle-like teeth in that they are good for gripping slippery fish! A good example of a shark with this tooth shape is the hooktooth shark.
But what about filter feeders – do they have teeth?
They sure do! There are three species of filter-feeding sharks: basking sharks, whale sharks and megamouth sharks, and they have rows of super tiny teeth on their upper and lower jaws that do not help them to chow down on anything. However, they might still be useful in helping the shark grip during mating!
Why do we find shark teeth so often?
Shark teeth are the most abundant vertebrate fossil in the world and are the most common body part that we find of ancient sharks. Why? Well, the rest of the shark is made up of cartilage, which doesn’t fossilise well. We have ancient shark teeth thanks to a process called permineralisation, which is a common form of fossilisation.
When a tooth is lost or the shark dies, it will sink to the bottom of the ocean and eventually become buried by sediment, which has no oxygen and so the tooth is preserved. As more and more sediment builds on top of the tooth, pressure begins to build up and forces mineral-bearing water into the tooth. The pH of the water may make some of the tooth begin to dissolve and minerals crystallise within its pores to form a fossil!
Why do shark tooth fossils come in so many colours?
The colour is determined by the type of sediment the fossil is preserved in! The tooth and the root are made of completely different substances, so they react differently to mineralisation. This causes the differences in colour between the tooth and the base.
Shahrouz Amini, et al., 2020, Shape-preserving erosion controlled by the graded microarchitecture of shark tooth enameloid
Lisa B Whitenack, et al., 2010, Young's modulus and hardness of shark tooth biomaterials
University of Vienna. Older than expected: Teeth reveal the origin of the tiger shark., ScienceDaily.