Soft Part Anatomy of Ammonoids: Reconstructing the Animal Based on Exceptionally Preserved Specimens and Actualistic Comparisons

Abstract

Soft-tissue preservation is very rare in ammonoids. The reconstruction of the internal anatomy relies on few specimens with exceptional preservation, comparisons with recent cephalopods, and inferences based on the extant phylogenetic bracket. Herein, we describe the current knowledge of the soft part-anatomy of ammonoids. Of the digestive tract, the buccal mass, oesophagus, crop, stomach and caecum are rarely preserved. Stomach contents have become known from eleven species. Remains of the cephalic cartilage are scarce and suggest the presence of a simple lens eye. Only little has become known of ammonite gill anatomy. Unequivocal imprints of arm crowns have not been discovered yet, but we reinterpreted a baculitid that possibly preserves an arm crown with (?) ten short and thin retractable arms. An ink sac was absent, while a hyponome was present. There is no evidence for a hood in ammonoids.