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Hybodus
''Hybodus'' ("humped tooth") is an extinct genus of widespread and long-lived sharks, first appearing towards the end of the Permian period, and disappearing during the Late Cretaceous. During the Triassic, Jurassic, and Cretaceous periods the hybodonts were especially successful and could be found in shallow seas across the world. For reasons that are not fully understood, the hybodonts became extinct near the end of the Late Cretaceous period.
==Description==
''Hybodus'' species grew to about in length, and are believed to have been opportunist predators. It was not very big, but had the classic streamlined shark shape, complete with two dorsal fins that would have helped it steer with precision. The mouth was not large, and rather than ruthlessly hunt large prey, ''Hybodus'', was capable of eating a wide range of foods. They had several distinct features that made them stand apart from other primitive sharks. Firstly, they had two different types of teeth, suggesting a wide diet. The sharper teeth would have been used to catch slippery prey, while the flatter teeth probably helped them crush shelled creatures. Secondly, they had a bony blade on their dorsal fin that probably served a defensive function. The males also possessed claspers, specialized organs that directly insert sperm into the female, and which are still present in modern sharks.
The youngest ''Hybodus'' fossils come from the Dinosaur Park Formation. They date from 68.6 to 66 million years ago.
The first fossilized teeth from ''Hybodus'' were found in England around 1845. Since then teeth (and dorsal spines) have been recovered from around the world.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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