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Parahelicoprion
''Parahelicoprion'' is an extinct genus of eugeneodontid, shark-like holocephalid from the Permian of the Ural Mountains and South America. Its name is a derivation of ''Helicoprion'', from the Ancient Greek words "Nearly coiled saw", another holocephalid that shares similar traits to it, including the helical whorl of teeth. One of the primary qualities that separate ''Parahelicoprion'' from the aforementioned ''Helicoprion'' is the shape, thickness and angle of the tooth whorl. This whorl sharks teeth protrude outwards not like a tightly coiled saw but instead a curved arrangement of cutting blades indicating it relied less on crushing slow-moving invertebrates and catching squid and other small mollusk prey, but inflicting traumatic damage against more durable, faster prey.〔http://dinonews.net/forum/paleoactus.php?msg=168926 Parahelicoprion and Agassizodontidea〕 Their teeth grew at a much slower pace than that of other whorl-tooth sharks, resulting in a depreciated spiral, growly only half of the teeth a ''Helicoprion'' would grow in its life time. The tooth spiral also was able to indicate the age of the eugeneodontidans in question. 〔Brad Matsen and Ray Troll (October 25, 2012). "Planet Ocean: A Story of Life, the Sea, and Dancing to the Fossil Record".〕
==Paleobiology==
''Parahelicoprion'' was a nektonic carnivore that preyed upon a variety of different species, using its blade-like teeth to cut at exposed flesh like a hatchet or wedge. Many different prey species were identified at the beginning of the Permian, from sarcopterygian fish ill-equipped to deal with large predators (''Menaspis'' and ''Petalodus'' being common prey items), xenacanthid sharks, plentiful species of ammonite and trilobite, and due to its size, other smaller eugeneodontids. ''Parahelicoprion'' is even believed to participate in cannibalism of its own species.
〔http://fossilworks.org/cgi-bin/bridge.pl?a=taxonInfo&taxon_no=34463〕
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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