How Many Teeth Does a Shark Have? Tooth Rows and Shedding

How are shark teeth arranged?

A shark’s teeth are not fixed in sockets the way human teeth are. They sit in the gums and are held in place by connective tissue, which is why they come out so easily. Along each jaw, the teeth form rows, one behind another.

Only the front row or two are upright and used for biting. Behind them lie several rows of replacement teeth at different stages of growth, folded back against the inner side of the jaw. When a front tooth breaks or falls out, the tooth behind it rotates forward and takes its place. In many species a lost tooth can be replaced within a day or two.

The number of teeth varies widely. The great white shark has about 300 teeth in total. Small catsharks and dogfish have many tiny teeth, while filter feeders have hundreds of rows of very small ones. The cookiecutter shark has only about 25–31 large teeth in its lower jaw, set side by side like the blade of a saw.

How often do sharks lose their teeth?

Shark teeth are always being lost and replaced. Teeth break on bones and shells, wear down, or simply drop out when a new tooth pushes forward. Depending on the species, a tooth may be replaced every 8–10 days or only every few months. Young sharks often replace teeth faster than adults.

Water temperature matters too. Experiments with nurse sharks found that teeth were replaced faster in warm water than in cold water, because a shark’s body runs faster when it is warmer.

Over a lifetime, the totals become enormous. Estimates for some ground sharks, the group that includes requiem and lemon sharks, run to about 30,000–35,000 teeth. The cookiecutter shark does something unusual: it replaces its whole lower row at once and swallows the old set, probably to recycle the calcium.

Different teeth for different diets

Tooth shape tells you a lot about what a shark eats. Scientists can often identify a species from a single tooth.

The tiger shark has some of the most remarkable teeth of any shark. Each tooth has a deep notch and a tip that points sideways, with coarse serrations along both edges. Combined with heavy jaws, these teeth let tiger sharks cut through the shells of sea turtles, one of their favorite foods.

Great whites change their teeth as they grow. Young sharks have narrower, pointed teeth for catching fish, while adults develop broader, more strongly serrated upper teeth for slicing large prey such as seals. The lower teeth stay narrower and help hold prey while the upper teeth cut.

Filter-feeding sharks barely use their teeth at all. The whale shark has more than 300 rows of tiny teeth, and the basking shark has rows of small, hooked teeth only 5–6 mm (0.2 in) long. Both feed by straining plankton from the water.

Teeth in the skin: dermal denticles

Sharks have “teeth” all over their bodies too. Their skin is covered in thousands of tiny scales called dermal denticles, which means “skin teeth”. Each denticle has the same basic structure as a tooth: a soft pulp center, a layer of dentine and a hard outer coating.

Denticles make shark skin feel smooth when stroked from head to tail and rough like sandpaper the other way. They protect the skin and channel water smoothly over the body, which reduces drag and helps sharks swim quietly and efficiently. Many scientists think the teeth of sharks and other vertebrates first evolved from scale-like structures similar to these denticles, although this is still debated.

Why fossil shark teeth are so common

Sharks have skeletons of cartilage, which rarely fossilizes, but their teeth are made of hard, mineral-rich material. Since each shark sheds thousands of teeth, the seabed has been collecting them for hundreds of millions of years. That makes shark teeth some of the most common vertebrate fossils. The reason sharks have no bones is explained in Do sharks have bones?

Fossil teeth are usually black, gray or brown rather than white, because minerals from the surrounding sediment replaced the original material. They turn up on beaches and in riverbeds in many places, including Florida, South Carolina, North Carolina and Maryland. The shark tooth is the official state fossil of Georgia.

The most famous fossil teeth belong to megalodon, an extinct giant whose largest teeth reach about 18 cm (7 in). For centuries in Europe, fossil shark teeth were called “tongue stones” and believed to be petrified snake or dragon tongues, until naturalists in the 1600s, including the Danish scientist Nicolas Steno, showed they came from sharks. What happened to megalodon is covered in Is megalodon still alive?

Myths and facts about shark teeth

Myth: sharks have hundreds of teeth in use at once. Most of a shark’s teeth are spare replacements lying flat behind the working rows.

Myth: shark teeth are made of bone. Teeth contain dentine and a hard outer layer, much like other vertebrate teeth, and sharks have no true bone in their bodies.

Fact: a shark tooth can be replaced within days. Constant replacement means sharks always have sharp teeth, even after biting into shells and bones.