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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 ...
Acrioceratidae is a family of heteromorph ammonites included in the Ancyloceratoidea comprising ancyloceratid-like forms that start off with a coiled juvenile section, followed by a straight or curved shaft ending in a hook.
Hamites ("hook-like") is a genus of heteromorph ammonite that evolved late in the Aptian stage of the Early Cretaceous and lasted into the Cenomanian stage of the Late Cretaceous. The genus is almost certainly paraphyletic but remains in wide use as a "catch all" for heteromorph ammonites of the superfamily Turrilitoidea that do not neatly fit ...
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 ...
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.
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Heteroceras is a genus of Lower Cretaceous heteromorph ammonites belonging to the ancyloceratoidean family, Heteroceratidae. [1] Description