Aberrant Ammonite Fossil Ancyloceras matheranianum Lower Cretaceous Russia
Abberant Ammonite Fossil, Ancyloceras matheranianum, Lower Cretaceous, Russia Ammonites are an extinct group of marine animals of the subclass Ammonoidea in the class Cephalopoda, phylum Mollusca. They are excellent index fossils, and it is often possible to link the rock layer in which they are found to specific geological time periods. Ammonites' closest living relative is probably not the modern Nautilus (which they outwardly resemble), but rather the subclass Coleoidea (octopus, squid, and cuttlefish). The majority of ammonite species feature a shell that is a planispiral flat coil, but other species feature a shell that is nearly straight (as in baculites). Still other species' shells are coiled helically, superficially like that of a large gastropod (as in Turrilites and Bostrychoceras). Some species' shells are even initially uncoiled, then partially coiled, and finally straight at maturity (as in Australiceras). These partially uncoiled and totally uncoiled forms began to diversify mainly during the early part of the Cretaceous and are known as heteromorphs.
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Photo credit: © Phil Degginger/Geo Enterprises / Alamy / Afripics
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Keywords: abberant, aberrant, ammonite, ammonitida, ammonitidae, ammonoidea, ancyloceras, cephalopod, chambers, cretaceous, extinct, extinction, fossil, fossils, jurassic, lines, matheranianum, mollusk, paleontological, paleontology, periods, russia, shells, spiral, suture
