APPLYING MORPHOLOGICAL EVIDENCE FROM EXCEPTIONALLY-PRESERVED HETEROMORPH AMMONOIDS TO RECONSTRUCT LIFE APPEARANCE AND BIODIVERSITY

Soft tissue preservation in ammonoid cephalopods is rare. The soft-part morphologies and paleobiology of heteromorph ammonoids (suborder ancylocertina) are especially difficult to understand due to their extreme shell shapes. Because more abundant forms, such as Baculites described by Landman get al. (2007) have a greater likelihood of being preserved with in-situ mouthparts due to their large numbers in the fossil record, it is often assumed that all heteromorphs may have fed on zooplankton. However, interpretations based on sedimentological associations, and shell form (e.g., suture geometry, mouth parts, muscle scars, and living chamber capacity) can direct the visual imaging of how heteromorphs looked and behaved. The aptychus (beak) of an in-situ Didymoceras nebrascense appears to be adapted for cutting and crushing larger prey (Kruta et al 2010.) However, Didymoceras’ limited nektonic agility may relegate its macrophagous species to ambush hunting and scavenging (Larson, 1997) and likely epibenthic floating (Peterman get al., 2020). By contrast to Baculites, Didymoceras may have fed on decapod crustaceans on the Western Interior Sea floor. Three separate mechanisms were examined in the extrapolation of heteromorph life appearance: stratigraphy, septal configuration (including suture geometry and living chamber dimensions,) and mouth-part adaptations.