This Specimen has been sold.
4.8 Inch Polished Madagascar Ammonite (Half)
Here is a 4.8 inch wide half of a Cleoniceras from Madagascar. It's Middle Cretaceous (110 million years) in age. Check out the inner chambers that have been replaced by pockets of crystals and the detail on the reverse side.
Ammonites were predatory mollusks that resembled a squid with a shell. These cephalopods had eyes, tentacles, and spiral shells. They are more closely related to a living octopus, though the shells resemble that of a nautilus. Ammonites appeared in the fossil record about 240 million years ago and they barely survived several major extinction events. The last lineages disappeared 65 million years ago at the end of the Cretaceous.