Introduction to Shark Fossils

Because sharks are made of cartilage rather than bone, many people assume that only their teeth can fossilize. While shark teeth are by far the most common fossils we find, they are far from the only remains sharks leave behind. Besides for shark teeth, parts of the skeleton made from denser cartilage can also preserve. These include the centers of vertebrae, sections of jaw cartilage, and even structures in the snout called rostral nodes. Shark skin is covered in tiny tooth-like scales called dermal denticles, and because they are made of similar materials to teeth, they can also fossilize under the right conditions. Some sharks even have fin spines that occasionally preserve in the fossil record. In rare cases, even shark feces, known as coprolites, can be found as fossils. Together, these different remains give us a much more complete picture of ancient sharks than teeth alone.

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Fossil Shark Teeth

Shark teeth are the most common type of fossil for a few simple reasons. First, like most vertebrate teeth, shark teeth are made of dentin, a hard, calcified tissue that does not easily decay. Dentin is denser and more durable than bone, and in a tooth it is protected by an even harder outer layer of enamel. Second, sharks are constantly replacing their teeth throughout their lives. As shown in the image above, new rows of teeth continuously develop behind the functional ones and move forward as older teeth are lost. A shark with 40 to 50 teeth in its front jaw can replace them every few weeks, meaning a single animal can shed tens of thousands of teeth over its lifetime. Estimates vary, but many sharks lose between 25,000 and 50,000 teeth in a lifetime. Multiply that across millions of sharks over tens of millions of years, and it becomes clear why shark teeth are by far the most common vertebrate fossil we find today.

Shark teeth can be categorized into three general shapes: crushing, grasping, and cutting. Crushing teeth are short and round. These are designed for crushing mollusk shells and crustaceans. Grasping teeth are long and pointy; ideal for grasping fleshy fish. Cutting teeth are usually triangular in shape and have serrations, like a steak knife, and are designed for cutting through bone and taking chunks out of large prey. The image below shows the general tooth shapes.

Shark teeth can also be grouped by where they sit in the jaw. The main positions are anterior (front), lateral (sides), and posterior (rear). Each of these tooth positions can look noticeably different, even within the same species. On top of that, tooth shape can vary depending on age and sex. Juvenile sharks often have different teeth than adults, and males and females of the same species can also show differences. Even the upper and lower jaws can produce teeth that look quite different from each other. All of these variations are shown in the image above. When you combine them, it becomes clear why isolated fossil teeth can be so difficult to identify to a specific shark species.

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Fossil Shark Vertebrae

Shark skeletons are made entirely of cartilage rather than bone. This is the same flexible material found in human ears and noses. Because cartilage is soft and decays quickly, complete shark skeletons are rarely preserved in the fossil record. The part of the skeleton most likely to fossilize is the vertebral centra, which are the disk-shaped centers of the vertebrae. These are the densest structures in a shark's body. In life, processes (small projections) would extend from grooves on the sides of each centrum, but these are rarely preserved. Shark vertebrae can vary widely in size. In small sharks, a centrum may be only about 1/8 inch across, while in giant species like Megalodon, they can reach 5 to 6 inches in diameter. Examples are shown in the image above. In most cases, isolated vertebrae cannot be used to identify a shark species. However, they do tend to fall into two general structural types: lamnoid and scyliorhinoid forms, which can sometimes provide broader clues about the type of shark they came from.

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Fossil Shark Cartilage

Although most shark cartilage does not fossilize, the cartilage found in the jaws is more likely to be preserved than other parts of the skeleton. Even so, it is still relatively rare compared to teeth and vertebrae. When it is found, fossil shark cartilage usually appears as small, broken fragments with irregular shapes. What makes it recognizable is its distinctive internal structure, which often shows a prismatic or crystalline pattern under close inspection. This texture helps distinguish it from surrounding rock and other fossils. A good example is shown in the image above.

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Shark Skin: Dermal Denticles

Dermal denticles are the tiny tooth-like scales that cover a shark's skin. They give sharks a unique texture—smooth when stroked in one direction, but rough like sandpaper in the opposite direction. This design also helps reduce drag in the water, giving sharks a hydrodynamic advantage while swimming. Each denticle is shaped a bit like a miniature tooth, with a root-like base anchored in the skin and a hard, enamel-like crown exposed on the surface. Because they are usually only about a millimeter in size, they are easy to overlook in the fossil record.

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Shark Rostral Nodes

The rostral node, also called rostral cartilage, helps form and support the shark's snout. It is located in the front part of the head, just beyond the nasal capsule, within the rostrum. In most sharks, this structure is cone-shaped and forms a dense block of cartilage that helps maintain the shape of the snout. In hammerhead sharks, however, the rostral cartilage is more expanded and squared off, matching the distinctive flattened head shape. A fossil example is shown in the image above.

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Fin Spines

Fin spines are exactly what they sound like: hard, spine-like structures that sit along the front edge of the fins in certain sharks. They were especially common in early Paleozoic sharks, but can still be found in some modern species, such as dogfish sharks. These structures are thought to have served mainly as a defense mechanism, helping deter predators. A fossil example is shown in the image above.

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Coprolite (Fossilized Shark Poop)

Coprolite is the scientific term for fossilized feces. In sharks, coprolites can vary widely in shape and size, but many show a distinctive spiral pattern formed as waste moved through the intestinal tract. Depending on what the shark ate, these fossils can sometimes contain fragments of bone or shell, offering direct clues about diet and feeding behavior. While it may seem surprising, coprolites can actually be quite common in certain fossil-rich layers.

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Conclusion

Although fossil shark teeth are the most common type of shark fossil, they are really just the beginning of the story. Sharks leave behind many other clues in the fossil record, from vertebrae and dermal denticles to cartilage fragments and even coprolite.

Each of these fossil types captures a different part of shark anatomy and behavior, helping paleontologists piece together how these animals lived, moved, and fed in ancient oceans. Taken together, they provide a much more complete picture of shark evolution than teeth alone can tell.

The next time you are collecting fossil shark teeth, take a closer look at the surrounding sediment. You might be surprised at what else is preserved there. Sometimes the most unusual finds are the ones you least expect-like a shark's nose cartilage or even fossilized "evidence" of its last meal. Even small fragments can be scientifically valuable, especially when they help fill gaps in our understanding of extinct shark diversity and anatomy. In many cases, it is these overlooked fossils that end up revealing the most interesting details about ancient marine ecosystems.

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