While longevity data are not available
for many sharks, maximum ages do vary by species. Some sharks like the smooth dogfish may only live 16 years, while others
such as the porbeagle shark, may live as long as 46 years. Whale sharks, now the largest fish in the world though they seem
to be shrinking in size, may well live over 100 years.
Sharks can shed and renew thousands of teeth during their life, this is why sharks teeth can be found washed onto beaches.
A young shark may lose a set of teeth in a week. 'Spare' teeth are ready to rotate forwards to replace broken or worn teeth.
They may have up to 3,000 teeth at one time. Most sharks have about 5 rows of teeth at any time.
They have lots of teeth arranged in layers so if any break off, new sharp teeth can immediately take their place. Shark
teeth also fossilize easily while the rest of the shark decomposes.
A shark's teeth are arranged in rows, the number of which varies from species to species. The row nearest the front of the
mouth is the "working" row of teeth (though some sharks use up to the first 8 rows of teeth), and they are the largest teeth
in a sharks' mouth. The second row of teeth is smaller than the first row of teeth, the third row of teeth is smaller than the
fourth row, and so on. Every time a shark loses a tooth, the tooth in the row behind it moves up to take the lost tooth's place.
This is possible because sharks' teeth are not embedded in the jaw, but are attached to the skin covering the jaw.
New teeth are continually grown in a groove in the shark's mouth and the skin acts as a "conveyor belt" to move the teeth
forward into new positions. Sharks' specialized teeth have allowed sharks to develop a very strong jaw. Without the ability to
quickly replace teeth, a shark's jaw could not have developed as powerful of a bite. The number of teeth they routinely lose
while catching prey would outweigh the quick-kill benefits of their crushing jaw strength.
Shark teeth have the same basic consistency as ours, but they don't sit in the mouth in the same way. Our teeth rest in
sockets and aren't replaced after childhood. Shark teeth are attached to the jaw by soft tissue and fall out all the time.
This is crucial to the shark's effectiveness -- worn or broken teeth are continually replaced by new, sharper teeth.
Sharks also have a very unique jaw structure which makes their mouths especially effective weapons. In most animals,
the lower jaw moves freely but the upper jaw is firmly attached to the skull. In sharks, the upper jaw rests below the skull,
but can be detached when the shark attacks its prey. This lets the shark thrust its entire mouth forward to grab onto
its prey. Jaw mobility varies among different species but all modern sharks have this ability to some degree. Most sharks
do not chew their food but gulp it down whole it in large pieces. The front set is the largest and does most of the work.
Sharks teeth come in many different shapes and sizes, as they are used to catch and kill different prey.
Some sharks have teeth that are very sharp, wide, wedge-shaped,
and serrated (having a jagged edge), designed for catching
and tearing apart prey (for example, the great white shark,
the tiger shark, the hammerhead and the bull shark). There
is a formula for calculating the size of a shark based on
the size of triangular tooth: measure the length of one side
of the tooth in inches, then multiply by ten to get the total
length of the shark in feet.
Some sharks have thin, sharp, knife-like teeth designed to
catch and hold slippery fish (for example, the lemon shark
and mako shark).
Many bottom-dwelling sharks have thick conical or flattened
teeth in the back of their mouths that are used for crushing
crabs and mollusks (for example, the nurse shark, Port Jackson
shark, angelshark, and zebra horn shark).