The Shark is a type of fish with a full cartilaginous skeleton and a highly streamlined body. They have several sets of replaceable teeth. The teeth of sharks are embedded in the gums rather than directly fixed to the jaw, and are constantly replaced throughout the shark's life.

Multiple rows of replacement teeth are grown in a groove on the inside of the jaw and moved forward in a "conveyor belt"; some sharks can lose some 30,000 teeth in their lifetime. The rate of tooth replacement varies from once every 8–10 days to several months. In most species teeth are replaced one at a time, while in the cookiecutter sharks the entire row of teeth is replaced simultaneously. The maximum lifespan of a shark varies from species to species. Most sharks live for 20 to 30 years.