The unique anatomy of sharks often sparks curiosity, particularly the apparent contradiction between their boneless bodies and their famously sharp teeth. Unlike most vertebrates, sharks possess a skeletal structure made of cartilage, not bone. This biological puzzle reveals fascinating adaptations that contribute to their success as marine predators.
Sharks’ Flexible Framework
Sharks belong to a group of fish known as cartilaginous fish; their skeletons are made primarily of cartilage rather than bone. Cartilage is a flexible and strong connective tissue, also found in parts of the human body like the nose and ears. This material is lighter and less dense than bone, providing sharks with an energetic advantage for swimming efficiently through water.
Cartilage consists of specialized cells called chondrocytes, which produce a matrix of collagen and other proteins. This composition allows cartilage to be durable yet flexible, enabling sharks to maneuver quickly and silently in their aquatic environment. While bone offers rigidity and support, cartilage provides a framework that is both robust and lightweight, which is particularly beneficial for a marine animal that lacks a swim bladder for buoyancy.
The Material of Shark Teeth
Despite their cartilaginous skeletons, shark teeth are highly mineralized structures. The outer layer of a shark’s tooth is made of an exceptionally hard, enamel-like substance called enameloid. This enameloid is primarily composed of fluoroapatite, a calcium phosphate mineral with a high fluoride content.
Beneath the enameloid lies dentine, a bone-like material that forms the bulk of the tooth. Dentine in sharks can vary, with some forms being compact and similar to human dentine, while others are spongier. The combination of these materials provides shark teeth with exceptional hardness and resistance to wear, making them effective tools for predation.
A Never-Ending Supply of Teeth
Sharks possess a continuous tooth replacement system, often described as a “conveyor belt” mechanism. Unlike humans who develop only two sets of teeth, sharks have multiple rows of teeth constantly developing behind the functional front row. As teeth in the front row are lost or damaged, new teeth from the rows behind move forward to take their place.
This process ensures that sharks always have a sharp and functional set of teeth. The rate of replacement varies among species, ranging from a few days to several months, and a single shark can shed tens of thousands of teeth throughout its lifetime. This regeneration is a significant evolutionary advantage, compensating for the frequent wear and tear experienced during hunting and feeding.
Teeth Built for Purpose
The shape and structure of shark teeth are highly adapted to their specific diets and hunting strategies. With over 500 species of sharks, there is a wide diversity in tooth morphology. For instance, sharks that feed on hard-shelled prey like crustaceans and mollusks, such as the nurse shark, often have dense, flattened teeth designed for crushing.
Conversely, sharks that primarily consume slippery fish, like mako sharks, possess long, needle-like teeth that are effective for grasping and piercing. Apex predators like the great white shark have triangular teeth with serrated edges, which are specialized for cutting through the flesh and bone of larger prey, including marine mammals. Filter-feeding sharks, such as the whale shark, have greatly reduced or non-functional teeth, as their feeding method does not require them.