Ammonite
digital model, mounted 3D print
Whenever we finish designing an ammonite, the same old doubts resurface. For as common and ordinary as they are in Jurassic and Cretaceous marine sediments, there are still major mysteries surrounding their appearance. The consensus now is that they likely had ten arms, possibly more highly derived eyes, and the ability to retract their soft body into the chamber of their shell with also incorporated buoyancy organ. But whether the eyes are shown too small, whether the arms are too thick, long, and bulbous, or whether the orientation is correct, these questions may never be answered.
Depicted here is an Aulacostephanus from the Late Jurassic. Although it did not have spines, it still ranks among the forms with pronounced shell sculpture.