Family Nautilidae ---

Vast fossil record!!

Nautiloids are first seen in the fossil record in the Cambrian period. They left an abundant amount of fossils, suggesting the few species that remain alive today signify a great reduction in their diversity. Due to the inability of their soft bodies to fossilize, the shells are what's used to understand the evolution, classification and early nautiloid morphology.
Nautiloids are the only cephalopod with a true external shell alive today (most have an internal shell or no shell at all).The first cephalopods likely had high, curved, conical, septate shells (like Goniatites) which were lost in most lineages. The extant species of Nautilus are thought to be very similar in shell to their ancestors.
Here are some of the more interesting fossils and their representations of mostly ancestral ammonids (cephalopods) indicative of their past diversity. More information on these drawings and more of them can be found here.