GEOFF KIDD / SCIENCE PHOTO LIBRARY GEOFF KIDD / SCIENCE PHOTO LIBRARY
Fossil shark tooth (Cretolamna biariculata). Example of the tooth of this Late Cretaceous (approx 70mya) mackerel shark. Sharks first evolved in the Palaeozoic era (570-245 million years ago). Shark's skeletons are formed of cartilage, a less durable material than bone, consequently there are few fossils of prehistoric sharks. Their teeth are made of a bone-like, enamel-coated substance that is more readily fossilised. The broad pointed shape indicates a probable diet of both bony fish and the marine animals that inhabited the oceans at this time. Cretolamna sp. are believed by many to be the direct ancestors of the giant Megalodon.
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