As you might have guessed, the number of teeth a shark has depends on the kind of shark. There are a lot of different kinds of sharks each that have different amounts of teeth. For example, a Great White Sharks has an average of 50 working teeth at any given time, though over the course of its lives can have up to 50,000 individual teeth.
Sharks are constantly shedding their teeth and growing new sets, a necessary feature for a carnivorous predator. Other kinds of shark can have up to 300 teeth at once. There are over 500 different known species of shark so that is a whole lot of teeth.
Shark teeth are a common find among fossil collectors due to their high amounts of calcium and phosphate minerals. In fact, shark teeth are the only part of a shark that will fossilize. Fossilized shark teeth can give evolutionary biologists clues about the evolution and biology of sharks. Analyzing shark teeth can also tell us a lot about the habits and diets of sharks. The exact shape and size of teeth tell us what kind of food they eat and help us trace out their life cycle and migration patterns.
Basic Facts About Sharks
The term “shark” is normally used to refer to any fish in the Selachimorpha superorder. Sharks are characterized by their cartilaginous skeletons, dorsal gills, and freestanding pectoral fins. Sharks range in size from the 17 cm dwarf lantern shark (Etmopterus perryi) to the massive 40-foot long whale shark (Rhincodon typus). Sharks find home in all the Earth’s oceans and live at mid-level depths, normally around 6,000 ft. Most sharks are saltwater but a few species live in both salt and freshwater.
Shark skeletons are very different from those of other ichthyoids. Where most kinds of fish have a bony skeleton, sharks instead have a skeleton made of almost entirely cartilage and connective tissue. They are similar to rays in this aspect. Shark cartilage is very flexible yet durable even though it is only half the density of normal bone. The lighter skeleton helps the shark save energy by reducing its weight.
A drawing of the skeleton of a Great White Shark. Credit: Public Domain
Sharks also have different scales than those of bony fish. Shark scales are made of fibers of collagen (the same stuff in human skin) that are crisscrossed in a helix shape across their whole body. The collagen fibers are what gives shark skin its recognizable rough textured feel. The skin both helps them move through water more quickly and anchors their swimming muscles to take strain off the skeleton.
Most sharks are obligate carnivores. Sharks are known for being fierce hunters and are generally the apex predator for their environment. They have an extraordinarily sensitive sense of smell that can detect blood in water at concentrations as low as one part per million. They can tell where their prey is by the timing and intensity when the scent hits each nostril (similar to human hearing). Combined with their good hearing, sharks are very effective predators. They are even able to sense electromagnetism generated by living organisms. Receptors near the nose called the ampullae of Lorenzini detect electrical signals. These electroreceptors assist them in locating prey.
Sharks take a long time to reproduce. Most sharks reach sexual maturity around 13-15 years of age and typically only rear a few well developed young. So far, sharks are the only kind of cartilaginous fish that is known to undergo parthenogenesis, meaning that the female can conceive asexually without the sperm of a male.
Kinds Of Shark Teeth
Sharks have very strong jaws and several rows of sharp jagged teeth. Their jaws are not actually connected to their heads and are surrounded by a layer of material called tesserae, small blocks of calcium salts. These tesserae act like armor and protect the jaws from damage.
Shark teeth are primarily made of calcium phosphate. These teeth are fused directly to the gums rather than the jaw so they can fall out and be removed easily. As such, sharks have a constant need for new teeth. In fact, an adult shark’s mouth typically has multiple rows of teeth that get pushed forward to take the place of a missing one. Most sharks have around 30,000 teeth during their whole 20-30 year lifespan, typically more for the longer-lived species. Sharks tend to replace their teeth more often when they are younger.
Shark teeth are counted in terms of rows (along the jaw) and series (from front to back). The average shark has about 15 rows and 5 series on both upper and lower jaws. The bull shark has 50 rows of teeth in 7 series. When a tooth in one row is lost, a tooth in a further series will sometimes be pushed into its space.
Shark teeth are specialized according to their diets. Some different kinds of shark teeth include:
Dense flat teeth
The dense flat teeth of the nurse shark. Credit: Public Domain
Sharks with dense flat teeth typically feed on hard shell bivalves like crustaceans and mollusks. The teeth are adapted for crushing and grinding and tend to be on the smaller side. Sharks that have flat teeth include nurse sharks and angel sharks. The plate-like teeth are specialized at the end to scoop up prey from the ocean floor.
Needle teeth
The needle teeth of a sand tiger shark. Credit; Public Domain
Needle teeth, as the name would imply, are sharp and pointed like needles. Needle teeth are shaped for pinning and gripping slippery prey, like the skin of other fish or aquatic mammals. Bull sharks have needle teeth which they use to feed on bony fish and small sharks, including other bull sharks. Bull sharks actually have the highest bite strength of all fish at 1,330 lbs.
Serrated teeth
The serrated teeth of tiger shark. Credit: Chris huh via WikiCommons CC-BY SA 3.0
Sharks that eat larger animals need teeth that can not only pierce and crush but also cut. That’s why these kinds of sharks have serrated teeth that have a sharp edge like a miniature saw blade. Sharks that have serrated teeth use them to cut the flesh of their prey into pieces for easier swallowing. Hammerhead sharks have serrated teeth that they use, along with their strangely shaped heads, to pin down and cut into their prey. Great White Sharks also have serrated teeth and feed on large sharks, dolphins, and even whales.
Non-functional teeth
Not all sharks actually use their teeth for feeding. Several species of shark like the basking shark and whale shark have small non-functional teeth. Instead of hunting and killing prey, they filter feed on plankton and krill by opening their mouths and sucking them in.
What Can We Learn From Shark Teeth?
Examining shark teeth can tell us a great deal about the lives of sharks. Primarily, shark teeth are used to differentiate a number of species. Species of shark are often grouped together based on tooth shape. The shared tooth shape normally signifies similar life patterns; e.g. they eat the same food, have the same predators, etc.
Most importantly, shark teeth help biologists trace out the evolutionary history of sharks. Shark teeth are the only part of a shark that will fossilize; the rest of the skeleton does not get preserved. As such, fossilized shark teeth are really the only clue we have as to the lives of ancient sharks. Patterns of shark teeth tell us about the ancestral relationships different shark species share and help us figure out exactly where sharks came from. Because shark teeth have a high mineral composition, they fossilize fairly easily and are among the more common discovered fossils.
All existing taxa of shark. Credit: Public Domain
The oldest discovered shark teeth date the first appearance of sharks to about 425 million years ago in the Late Ordovician period. The first sharks lacked the collagen fiber scales and had different mouth placements than modern sharks. Sharks have been top-level predators throughout their entire existence and have survived every single mass extinction event in Earth’s history.
Anatomically modern sharks appeared about 100-200 million years ago in the Jurassic and Cretaceous periods. The oldest modern shark is the cow shark that dates back to 190 million years ago. This period of time was also home to the largest shark to have ever existed, the Megalodon shark. Megalodons likely measured over 50-feet long and had a bite strength of up to 40,000 lbs. They had incredibly thick tough teeth that measured on average about 7 inches across, about the size of your entire hand. The most recent species of shark is the hammerhead shark which emerged about 50-35 million years ago. So overall, sharks have been on Earth 100 times longer than humans and over three times longer than the dinosaurs.
A megalodon tooth compared to Great White tooth. Credit: B. Inaglory CC-BY SA 3.0
Shark Teeth And Humans
Shark teeth have a long history of being used by humans as tools or for decorative purposes. In Oceania and the Pacific islands, shark teeth were used to carve and chop wood, prepare food, and as weapons. For example, the leiomano is a shark tooth tipped club that was used by native Hawaiians as weapons. Fossilized shark teeth are highly sought after by collectors and entire industries exist that trade in shark teeth.
Unfortunately, many species of shark are currently classified as vulnerable or endangered by the WWF. The majority of these cases are due to human overfishing which disrupts the marine food chain. Sharks themselves are also frequently hunted as they are considered a delicacy in some parts of the world. Changes in the temperature and acidity of the oceans due to climate change also pose a threat to shark habitats.