 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.Perhaps the most extreme and bizarre-looking example of a heteromorph is "Nipponites", which appears to be a tangle of irregular whorls lacking any obvious symmetric coiling.