30 Sharks: The Animal Answer Guide
functional, although this number can range as high as eight. The number
of tooth rows differs among species: some rays have only one row in each
jaw, whereas Whale Sharks have more than 300 rows of very small teeth.
Most sharks have 20 to 30 tooth rows, meaning 10 to 15 functional teeth
on either side of each jaw. Teeth can also serve different purposes during
their “functional” life. The functional teeth of the Spotted Eagle Ray, Ae-
tobatus narinari, consist of a central group of fused teeth in the upper and
lower jaws that are used for crushing prey. However, as these teeth are
replaced from behind, the lower-jaw teeth move forward, become shovel-
like, and are used to dig up prey.
The pattern of replacement also differs among species. Some sharks,
such as White Sharks and hammerheads, replace teeth individually as they
are worn out or lost. Squaloid sharks such as Spiny Dogfish, Greenland,
and Cookiecutter Sharks replace entire rows regardless of use; replacement
teeth in interior rows continue to grow and move forward, eventually dis-
placing or replacing functional teeth. Teeth also grow as the shark grows.
Teeth in the internal rows are therefore larger than the functional teeth
about to be replaced.
We know from sharks kept in captivity how often replacement occurs
and therefore can estimate the number of teeth a shark may have during
its lifetime. Replacement rates vary tremendously among families and spe-
cies, occurring every few days to every month. Rates also differ between
young and old individuals of a species, younger sharks replacing teeth more
often. Seasonal differences also occur, with teeth replaced more often dur-
ing summer than winter, as in Nurse Sharks, which replace teeth every 9
to 28 days in summer but every 51 to 70 days in winter. Sand Tigers (Car-
charias taurus) replace a functional tooth about every 2 days, Lemon Sharks
every 8 to 10 days, Leopard Sharks (Triakis semifasciata) every 9 to 12 days,
Horn Sharks (Heterodontus francisci) every 28 days, and the Small-spotted
Catshark (Scyliorhinus canicula) at 5-week intervals. From these numbers,
it has been estimated that a shark produces about 30,000 teeth during its
lifetime, although the actual number remains unknown for most species.
Do a shark’s teeth change during its life?
A shark’s teeth are generally appropriate for the kind of food it eats. It
is not surprising then that some sharks that change their diet also change
their tooth type (although Bull Sharks change from a fish-heavy diet to a
diet that includes tougher foods such as marine mammals and sea turtles by
developing a stronger bite rather than different teeth). A good example of
a tooth changer is the White Shark, which switches from a diet of mostly
fish when it is less than 3 m (10 ft) long to a diet that includes marine mam-
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