PAUL D STEWART / SCIENCE PHOTO LIBRARY PAUL D STEWART / SCIENCE PHOTO LIBRARY
Asteroceros stellare ammonite from the Jurassic Frodingham Ironstone, Scunthorpe, UK. Showing distinctive pattern of ammonitic fossilised chamber sutures preserved in calcite. The outer shell layers have been polished away. These sutures tended to get more complex over evolutionary time among the ammonites, which is an aid in field dating rocks. The purpose of these complex sutures is still unknown.
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