Crioceras duvali
Early Cretaceous (Hauterivian)
Drôme, Rodano-Alpes, France

65mm heteromorph ammonite on 195mm matrix

Crioceras is a well known heteromorph ammonite, a type of ammonite with an unorthodox, non-spiral shell shape. Unlike the typical planispiral coiling of most ammonites, heteromorph ammonites exhibit a variety of shell forms, including straight, hooked, or loosely coiled configurations. These unique shapes are thought to have evolved multiple times independently within different lineages of ammonites during the Cretaceous period. The varied shell forms of heteromorph ammonites are often used in studies of evolutionary biology and paleontology to understand the diversity and adaptability of ancient marine organisms.