5 Inch, Scarce Desmoceras Ammonite

Desmoceras is a genus of ammonite from Madagascar much less frequently seen than the common Cleoniceras. It's much thicker and wider with this specimen being almost an inch and a half thick at it's widest and 5 inches in diameter. It's Early Cretaceous (Albian Stage) in age or approximately 110 million years old.

Ammonites were predatory mollusks that resembled squids with shells. These cephalopods had eyes, tentacles, and spiral shells. Though their shells resemble that of a nautilus, they are actually more closely related to living octopuses. Ammonites appeared in the fossil record about 240 million years ago, barely surviving several major extinction events. The last lineages disappeared 65 million years ago at the end of the Cretaceous.

Artist's reconstruction of an ammonite, by Nobu Tamura

More about ammonites