Cephalopod Convergent Evolution

Organisms can share features as a result of convergent evolution. While natural selection, the process by which individuals reproduce more successfully at a higher rate than others individual organisms generally drives evolution, convergence occurs when distantly related species of organisms develop similar structures in response to similar environmental challenges.
 
Here are some examples to illustrate the concept. Nautiloid cephalopods are known to have a straight or "orthocone" shape. Bactritids are a family of Goniatites that evolved from Nautiloids and lived in the early Devonian period (about 400 million years ago). Bactritids are the ancestors of the first ammonoids to form into the "criocone" (coiled) shape that ammonites are typically recognized for developed into. Xenodiscus, a Ceratid ammonoid, is the only criocone ammonoid to survive beyond the Permian mass extinction. Xenodiscus is considered the parent of all Mesozoic ammonoids.
 
250 million years later, just prior to the Cretaceous period, criocone ammonites evolved to form an uncoiled shape. Their decendents became the orthocone Bochianites family, members of the strangely shaped heteromorphic anclyoceratids.
 
40 million years later, the C shaped Hamites of the anclyoceratids straightened out into the orthocone Baculites.
 
Another morphological example that supports convergent evolution is of the comparable sutures of a goniatite, an ammonoid that died 250 million years ago, and the Aturia, a species of nautiloid from 40 mya.
 

Below are illustrations of fossils that embody convergent evolution.

Othocone Nautiloid Bactrites sp. Xenodiscus sp. Bochianites neocomiensis

Hamite sp Baculites scotti Muensteroceras oweni Aturia sp.