They swam in ancient oceans from the Devonian Period, about 400 million years ago, to their extinction along with the dinosaurs in the Cretaceous Period, 65 million years ago.Īmmonites were free-floating invertebrates that were attacked by plesiosaurs and mosasaurs, two groups of gigantic marine reptiles.
They were a wildly successful animal, plentiful and diverse. Some lived longer becoming very large.Īmmonites belong to the Mollusca phylum in a class known as cephalopods – “head-footed” creatures such as octopus and squid. Ammonites first show up in the fossil record during the Devonian Period. They also grew quickly with the females growing up to 400% larger than the males because they needed the larger shell for egg production. They fed on plankton and quickly assumed a strong protective outer shell. If an ammonite is found in clay the clay will preserve the Ammonites mother-of-pearl luster.Īmmonites began life very tiny, less than 1mm in diameter, and were vulnerable to attack from predators. Because of their rapid evolution and widespread distribution, they are an excellent tool for indexing and dating rocks. And come in every naturally occurring color. Then they began to thrive from the Jurassic period until the end of the Cretaceous period when all species of ammonites became extinct.Īmmonite fossils are found on every continent. They went on to flourish throughout the Triassic period, but at the end of this period (206 million years ago), all but one species died. The first during the Permian period (250million years ago), only 10% survived. Ammonites lived during the periods of Earth history known as the Jurassic and Cretaceous. During their evolution, three catastrophic events occurred. Ammonites can be 65 to 200 million years old. They are cephalopods and first appeared in the seas 415 million years ago, in the form of a straight-shelled creature known as Baculites. Ammonite is a name that comes from the Greek ram-horned God called Ammon are the most widely known fossil.
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