Types of Skeletons in Sharks
Sharks have changed very little over millions of years in existence. They date back to the dinosaur days, and even the older versions had adaptations that distinguished them from other ocean predators. One of those is the skeleton, which is not made up of bone.
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Cartilage
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Sharks don't have actual bones. They're held together by cartilage, the tough but flexible substance also found in human ears and noses. Cartilage is light enough to help a shark maintain neutral buoyancy in the water, but strong enough to give the shark a frame. Each of the five fin types of a shark, the pectoral, dorsal, pelvic, anal and caudal fins, is rigid because it is filled with cartilaginous rods. The lack of true bone in shark skeletons means it is very rare to find a shark fossil intact.
Shark Scanning
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True shark skeletons have been found in the chalk deposits of western Kansas, where the chalk preserved the fragile cartilage. One shark fin unearthed there was the first proof that a large, plankton eating shark existed with the dinosaurs about 85 million years ago. Other skeletons provide clues to why some species didn't survive. For example, by scanning fossils, researchers can see differences in the tail structure. From that they can tell if the shark was a fast or a slow swimmer.
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Makos and Megalodons
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Marine biologists have long argued that the great white shark is a smaller relative of the mammoth megalodon shark, an extinct behemoth thought to have reached 60 feet long. The counterargument placed the shark in the wide-toothed mako camp. A fossil found in 1988 in Peru helped settle the argument. It was the entire jaw of an early white shark with the teeth attached. The extremely rare find of jaw cartilage and the placement of the teeth allowed scientists to approximate the shark's age and size. By comparing that information to other fossil evidence, they were able to rule out the megalodon connection. The white shark's 222 teeth and the growth rings in its 45 vertebrae closely match those of mako fossils.
Oldest Intact Skeleton
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The complete fossil of a tiny, 409-year-old shark, including a well-preserved skeleton, scales and brain, was discovered in 1997 by paleontologists from Canada's New Brunswick Museum. It was found in an area of New Brunswick that was once an estuary south of the Equator. The small fossil, which apparently sank into heavy sediment where it lay undisturbed, gave scientists a better understanding of the evolution of the shark. One surprising finding was the teeth were arranged in multiple rows, just like they are in modern sharks.
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References
- Photo Credit shark image by Irena Hnidkova from Fotolia.com
