Ammonites first appearing in the fossil record 240 million years ago, descending from straight shelled cephalopods. The last lineages disappeared 65 million years ago at the end of the cretaceous. Ammonites are an extinct group of marine mollusks that thrived in earth’s oceans for millions of years.
Learn about their evolution, shell structure, fossilization, and role as key index fossils in geology. Ammonites were marine animals belonging to the phylum mollusca and the class cephalopoda. Fossilization occurred when shells were buried in marine sediments and the original aragonite was replaced by other minerals.
In the new ammonite specimen, round structures interpreted as fossil remains of ovaries are well visible.
Ammonite shells are used today as index fossils, meaning they can help date other fossils that are found in the same layer of marine rock. These fascinating creatures left behind an extensive fossil record that provides. Due to their durable aragonite shells, ammonites fossilized prolifically. They had a coiled external shell similar to that of the modern nautilus.
Ammonites were shelled cephalopods that died out about 66 million years ago. In other living cephalopods, e.g. The name ammonite, from which the scientific term is derived, was inspired by the spiral shape of their fossilized shells, which somewhat resemble tightly coiled rams ' horns. Fossils of them are found all around the world, sometimes in very large concentrations.
