8.4" Polished Jurassic Ammonite (Perisphinctes) - Madagascar
This is a 8.4" wide ammonite (Perisphinctes sp.) fossil that was collected near Sakaraha in the Tulear Province of Madagascar. It is Jurassic (Oxfordian Stage) in age or approximately 160 million years old. It has a well defined ribbing and it's quite heavy for its size. The exterior has been lightly polished and it comes with an acrylic display stand.
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. True ammonites appeared in the fossil record about 240 million years ago. The last lineages disappeared 65 million years ago at the end of the Cretaceous.