In the Pacific and Indian Oceans, a relative of the squid still lives today whose shell is very similar to that of the ammonite: the nautilus. It also has a spirally coiled and chambered shell.

For a long time, researchers therefore assumed that Ammonites and Nautiloids were very closely related. Recently, however, there has been increasing evidence that Nautilus is less closely linked to our ammonites than any other modern squid.

Although fossil nautiloids are generally rarer than ammonites, they also occur in almost all strata in which ammonites have been found. Unlike ammonites and dinosaurs, they survived the great extinction 66 million years ago.