The first ammonites appeared 240 million years ago and were descendants of cephalopods that lived 415 million years ago. Many ammonite fossils are found due to the species' heavy breeding.
Ammonites were squid-like creatures that were named for Ammon, an Egyptian god. They were carnivores that grew to be around 3 feet in diameter. Female ammonites were around 400 percent larger than males. According to National Geographic, the difference in size may have been due to the females' need for room to lay eggs.Learn more about Zoology