 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.Fossils of "Ancyloceras" species are found in the Cretaceous Barremian Stage (117-113 million year old) marine strata of Europe and Morocco.