Heteromorph Ammonites: Ancyloceratina Anatomy: Ammonites were a diverse group of Not much about Ancyloceratina sea-dwelling spiral shelled molluscs anatomy can be determined from the first arising in the Devonian thought fossil specimen. However, we do to be most closely related to modern know that Ancyloceratina is most cephalopods [1] [4]. Ammonites commonly five-lobed [2]. We also survived three mass extinctions, know that they had strange shell finally dying at the K/Pg Extinction. forms, commonly uncoiled [1]. Their Ammonites ancestrally have a strange uncoiled spiral shape would planospiral (simple spiral) shell be far less advantageous to structure (we call these swimming than the tightly coiled monomorphs), but throughout their planospiral shape [1]. Because of history they have also developed Monomorph [4] Ancycloceratina [4] this, we believe that heteromorph more strange and complex shell ammonites would have been very forms [1] [4]. These ammonites are poor swimmers [1]. Ancyloceratina called Ancyloceratina or heteromorph Caspianites wassiliewskyi: also had a lot of variety in shell ammonites, and they first arose in ● Heteromorphic origin of the monomorph shape [2]. the late Jurassic, becoming more Deshayesitoidea [2]. common and geographically diverse ● Crescent-like cross section replaced in the during the Cretaceous [1]. While first whorl [2]. Ancyloceratina are ancestrally ● Reduced first umbilical lobe and the return heteromorphs, there are some of a four-lobed structure, transitioning to a species that are convergent planospiral shell [2]. monomorphs. ● Appearance of umbilical perforations [2] The crescent-like cross-section of the first whorl in the suborder Ancyloceratina is reduced to a rounded cross-section. A Retrieved from Ebel-k five-lobed primary suture is typical for most ancyloceratids, though it may be unstable [3]. Prey and Predators: Most Ancyloceratina were planktonic, rather than benthic or nektonic [2]. Retrieved from Fossil Mall They preyed on plankton while they Paleontologists knew very little about themselves were preyed on by marine Anocycloceratina until new recent reptiles such as mosasaurs [1]. advances in tools and techniques for extracting fossil specimen allowed Lauren Brann, Scott Spause, Yuewen Chen them to safely extract these more Caspianites [3] Deshayesitoidea Geol 204 The Fossil Record r/ complex fossil ammonites. Retrieved from Ammohildo Spring 2019 Section 0103.