The idea that a shark’s tooth is made of bone is a common misunderstanding rooted in the fact that teeth and bones are both highly mineralized tissues. Unlike the skeleton that supports the shark’s body, which is made of flexible cartilage instead of true bone, a shark’s teeth are not osseous tissue. They are specialized structures composed of materials that differ significantly from the bone found in mammals, providing a unique combination of hardness and resilience perfectly suited for a predator’s mouth. This structural specialization allows them to withstand the constant stress of feeding and explains why they are the most common shark fossil found today.
The Direct Answer: Composition and Structure
Shark teeth are primarily built around a core of dentin, a calcified tissue that has a structure similar to bone but is much harder and denser. Dentin supports the structure of the tooth and makes up the bulk of its mass. Depending on the species, the dentin can be categorized as orthodentine (more compact) or osteodentine (vascularized and sponge-like).
The outer layer of the shark’s tooth, which is analogous to human enamel, is a unique substance called enameloid. While human enamel is composed of hydroxyapatite, the outer coating on a shark’s tooth is a hyper-mineralized crystalline material known as fluorapatite. This fluorapatite naturally incorporates fluoride, making the tooth resistant to the acids that cause decay and erosion. This outer layer is one of the hardest mineralized tissues found in the animal kingdom, providing a durable, razor-sharp edge for tearing prey.
The Conveyor Belt System
The continuous supply of teeth in a shark’s mouth is maintained by a specialized system often described as a “conveyor belt.” New teeth constantly develop in rows deep within the jaw, folding backward toward the inside of the mouth. As a tooth in the functional front row is lost, the tooth directly behind it rotates forward to take its place.
This replacement process is rapid, ensuring the shark always maintains a sharp set of weapons for hunting. The speed of replacement varies based on the shark’s age, species, and water temperature, ranging from a few months to as little as 8 to 10 days in some species. A single shark may shed and replace an astonishing number of teeth over its lifetime, with some species estimated to go through 25,000 to 50,000 teeth. This cyclical shedding explains why fossilized shark teeth are so abundant.
How Shark Teeth Differ From Human Teeth
The most significant distinction between shark teeth and human teeth is their attachment and replacement mechanism. Human teeth are anchored into sockets within the jawbone, relying on deep roots for stability. This arrangement makes human teeth permanent, with only one set replacing the initial baby teeth.
In contrast, shark teeth do not have deep bony roots; they are instead superficially embedded in the connective tissue or skin of the jaw. This loose attachment facilitates their easy and frequent replacement. Humans are classified as diphyodonts (having two sets of teeth), while sharks are polyphyodonts, meaning they have a continuous, lifelong succession of replacement teeth. The physical difference in the outer mineralized layer also contributes to their function, with the shark’s highly durable fluorapatite coating providing superior hardness and resistance to erosion compared to the hydroxyapatite that forms the outer layer of human enamel.