Structure

• Shark teeth do not form along the jaw like most vertebrates or even the gums, but instead they form along a membrane inside of the jaw. The embedded root grows after the crown cap has already developed, and the entire tooth is covered by a layer of enamel. Each tooth may grow up to a few inches in length depending on the size of the shark, and they exist in multiple rows within the mouth.
  
  

Teeth Replacement

• Teeth are constantly replaced during the shark's lifetime. This is a phenomenon known as polyphyodont dentition. Each replacement tooth pushes the membrane forward and is slightly larger than the one that just preceded it. Some sharks may have up to 35,000 teeth during a single lifetime, but some have different methods of replacement. For instance, the Great White Shark replaces teeth individually, and the Cookiecutter Shark replaces them wholesale.
  
  

Serrated Teeth

• The structure of shark teeth are highly variable from species to species. The prominent Great White Shark has large triangle-shaped teeth with serrated edges. Other sharks with serrated teeth include the Great Hammerhead Shark, Bull Shark and Tiger Shark, the latter of which has a distinctly notched curve that is suitable for both power and tearing, especially through the tough carapace of sea turtles; however, most of these sharks prefer to eat mammals and large fish.
  
  

Non-Serrated Teeth

• The Sixgill Shark has a unique arrangement; its lower teeth are comb-like, but its upper teeth are shaped like spikes. Sandtiger Sharks have nothing but spiked teeth with two small, secondary cusplets on either side of the main blade. These kinds of sharks feed on squid and fish, but there are also other kinds. Clam and crab eaters have flat, crushing teeth, and plankton eaters barely have any teeth at all.
  
  

Fossilization

• Fossilized teeth are the best and most frequent remnants from ancient sharks. Because the rest of the shark is made out of cartilage, it tends not to fossilize as well as bone. Sharks are ancient creatures that come in many unique permutations. The megalodon, for instance, lived approximately 25 to 1.6 million years ago and had teeth up to 17 cm (7 inches) in length.