This is a beautiful ammonite fossil of the genus Taramelliceras sp., collected from the Gräfenberg Quarry of Bavaria, Germany. It's upper Jurassic in age, or approximately 155 million years old. The majority of the rock surrounding the ammonite has been cleaned away.
The Gräfenberg Quarry is famous for the green ammonites (mostly Ardescia) that are found within the sedimentary rock. The green coloration of the ammonites is caused by the mineral glauconite. When exposed to weathering or erosion, glauconite will change color to orange, brown and/or yellow.
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.