The earliest ammonoids on Earth, small organisms called Bacrites, had straight shells. Later ammonites had coiled shells made up of a spiraling series of chambers. They got their name from early Romans who mistook their fossils for ram?s horns (Ammon= a god with ram's horns). Ammonites became common in the seas of the Jurassic (200 million years ago). They were top predators, feeding on fishes, mollusks, arthropods, or other ocean creatures. Ammonites used good eyesight and tentacles to capture prey and feed it into a strong, crushing beak. Their closest living relatives are probably the modern nautiloids, but ancient ammonoids could be wider than a minivan. During the Cretaceous (about 150 million years ago), as ammonoids reached their heyday, some evolved to have shells that were coiled less or not at all. All ammonoids went extinct in the huge extinction event at the end of the Cretaceous (65 million years ago).