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The biology of the heteromorph ammonites is not clear, but one certainty is that their uncoiled shells would have made these forms very poor swimmers. Open shells, particularly ones with spines and ribs, create a lot of drag; but more importantly, the orientation of the shell, with the body hanging below the buoyant part of the shell, would ...
They are known as heteromorph shaped, with a partly uncoiled shell and the aperture directed toward the coiled part. Most ammonites are homomorph, as they maintain the same shape throughout the growth, while the ammonites in this genus have uncoiled shells ( heteromorph or different-shaped ammonites), that would have precluded fast swimming.
Heteromorph ammonite Didymoceras stevensoni Life restoration of the heteromorph ammonite Diplomoceras with the plesiosaur Aristonectes Life restoration of the heteromorph Hyphantoceras Ammonoids with a shell shape diverging from the typical planispiral form are known as heteromorphs , instead forming a conch with detached whorls (open coiling ...
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Polyptychoceras is a heteromorph ammonite, meaning that its shell does not curl up into the tight spiral shape which shells of ammonites from the subclass Ammonoidea typically do. Polyptychoceras shells have an abrupt weight increase after formation of the initial shaft, which represents the shell's automatic balance condition. [ 4 ]
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Nostoceratidae is a diverse family of heteromorph ammonites found throughout the oceans of the world during the Late Cretaceous. The nostoceratids are famous for the bizarre coiling of their shells. The nostoceratids are famous for the bizarre coiling of their shells.
Bostrychoceras is a genus of heteromorph ammonite from the family Nostoceratidae. Fossils have been found in Late Cretaceous sediments in Europe and North America.. The shell of Bostrychoceras begins as a tightly wound helical spire, like that of Nostoceras, from which hangs a U- or J-shaped body chamber, at least in the adult.