A great temple to the god Amon was built at Karnak in Upper Egypt around c. 1785. It is from Amon that we get his cephalopod namesake, the ammonites and also the name origin for the compound ammonia or NH3. Ammonites were a group of hugely successful complex molluscs that looked like the still extant Nautilus, a coiled shellfish that lives off the southern coast of Asia. While the Nautilus lived on, ammonites graced our waters from around 400 million years ago until the end of the Cretaceous, 65 million years ago.
Varying in size from millimeters to meters across, ammonites are prized as both works of art and index fossils, geological time markers, helping us date rock. They have proven especially useful for proving time markers for the strata of the Cretaceous System along the west coast of North America.
The ammonites with their hard exoskeleton, chambers and soft interior, were kissing cousins in the Class Cephalopoda, meaning "head-footed," closely related to modern squid, cuttlefish and octopus. Cephalopods have a complex eye structure and were excellent swimmers. Ammonites used these evolutionary benefits to their advantage, making them one of the most successful marine predators of ancient Cretaceous seas.
