Ammonites are extinct ancestors of modern day squid and cuttlefish. They have shells that look like tightly-wound ram horns and probably live just off the sea bottom. They are believed to be herbivorous. They first appeared about 400 million years ago, about the same time that terrestrial plants first appeared. They became extinct about 65 million years ago, just when dinosaurs began to roam the earth.

The specimen I photographed is prettier than most: a petrified ammonite shell with leaf-like patterns inscribed all over. This beautiful pattern is likely for camouflage, helping it disappear within an aquatic habitat that probably looks like a leafy aquatic forest.

But wait, look closer. You will see two different leaf-shapes: rounded and jagged-edged, each one moving in an opposite direction, creating an endless illusion of two types of leaves trying to out-grow each other! What a grand work of art, this optical illusion! Which leaf shape did you initially see? Enjoy.