Shark teeth are fundamentally different from the teeth of mammals, serving as a record of a shark’s diet and its long history in the ocean. Their unique composition and continuous replacement make them successful instruments for a wide variety of marine predators. They represent one of the most common fossil finds, providing scientists with valuable insights into the past.
The Unique Composition of Shark Teeth
Unlike human teeth, which are rooted in the jawbone, shark teeth are not anchored by a bony root, but are embedded directly in the gingival tissue. The structural makeup consists of two main tissues: a core of dentine and an outer layer of enameloid. Dentine is a mineralized, bone-like tissue, while the enameloid layer is an extremely hard, hypermineralized covering.
This outer enameloid layer is not true enamel, but a distinct tissue composed of fluoroapatite, a highly resistant mineral that incorporates fluoride. This chemical composition makes the surface of the tooth exceptionally durable against the forces of biting and the corrosive effects of seawater. The enameloid covers the crown of the tooth, protecting the softer dentine core, which contains a higher content of organic matter.
Diversity in Shape and Function
The appearance of a shark’s tooth is directly related to its diet, showing remarkable diversity across the 500-plus species of sharks. These variations are broadly categorized into distinct forms, each suited for a specific feeding strategy.
One common type is the long, slender, and needle-like tooth, exemplified by Mako or Sand Tiger sharks. These teeth are designed for quickly gripping slippery prey, such as fast-moving fish and squid, which are often swallowed whole. The slender shape pierces the prey, preventing escape without the need for a serrated edge.
Another distinctive form is the broad, triangular, and heavily serrated tooth, famously seen in the Great White and Tiger sharks. This morphology is adapted for cutting and tearing through the thick flesh and bone of large marine mammals and other sharks. The sharp serrations act like a steak knife, allowing the shark to slice off manageable portions for swallowing.
A third major type is the dense, flattened, or pavement-like tooth found in species like the Nurse and Horn sharks. These short, blunt teeth form a crushing plate rather than a cutting edge. Their function is to crack open the hard shells of crustaceans, mollusks, and other bottom-dwelling, armored prey. This specialized dentition allows the shark to access otherwise inaccessible food sources.
The Mechanism of Tooth Replacement
Sharks possess a continuous tooth replacement system known as polyphyodonty, which ensures they always have a fresh, sharp set of teeth. New teeth develop in multiple rows deep within the shark’s jaw, forming a reserve supply. Most sharks have multiple rows of teeth in their mouth at any given time, often ranging from five to fifteen rows.
This system works much like a natural conveyor belt, with developing teeth constantly moving forward from the inside of the jaw towards the edge. When a tooth in the active outer row is lost or damaged during feeding, the tooth directly behind it rotates forward to take its place. This replacement can occur rapidly, sometimes taking only a few weeks, though it is faster in younger sharks or in warmer water.
Some species, like the Tiger or Hammerhead sharks, may shed and replace up to 35,000 teeth over their lifetime. This constant replacement mechanism constantly renews the shark’s primary hunting tools without the need for extensive healing time.
What Fossilized Shark Teeth Reveal
Fossilized shark teeth are common vertebrate fossils because their highly mineralized enameloid resists decay far better than the shark’s cartilaginous skeleton. When a tooth is shed and sinks to the ocean floor, it becomes buried in sediment, triggering the process of permineralization.
During permineralization, minerals like iron and manganese from the surrounding sediment seep into the porous dentine, gradually replacing the original organic material. This mineral absorption causes fossilized shark teeth to acquire their characteristic dark coloration, typically appearing black, gray, or brown. The specific color depends on the unique mineral composition of the sediment where the tooth was preserved.
The most famous examples are the teeth of the extinct Megalodon, which can measure over 17 centimeters (seven inches) in length. These massive, triangular fossils dwarf the teeth of modern sharks, providing evidence of the enormous size this ancient apex predator reached. The discovery of these preserved teeth allows scientists to trace the evolutionary history of sharks over hundreds of millions of years.