Extinct mollusks with a coiled, flat, chambered shell
This group of extinct invertebrates (animals without backbones) are related to the present-day squid, octopus and nautilus. They inhabited the oceans for over 350 million years, becoming extinct 65 million years ago. They are used as index fossils (fossils so common that they help to identify others found with them). Some ammonites grew to four feet or more in diameter, and many had chambered and coiled shells.
a marine animal with a spiral coiled shell. Found as fossils in marine sediments from the Lower Devonian to Late Cretaceous periods of geological time.
An ammonoid of the order Ammonitida, in which the suture pattern is complex (both the lobes and the saddles are intricately folded). They range in age from the Ordovician to the Cretaceous. ( Ammonoids)
One of the most popular fossils among collectors because they can be very beautiful, ammonites are extinct sea-dwelling molluscs of the group called cephalods; their living relatives include octopus and squid. Their hard external shells preserve well as fossils, and they are very useful in dating rocks because they evolved rapidly and individual species were only around for a short time before dying out and being replaced by another ammonite species. The shape of ammonites meant that in folklore they were thought to be the remains of coiled snakes.
A group of fossil, spiral, chambered shells, allied to the existing pearly nautilus, but having the partitions between the chambers waved in complicated patterns at their junction with the outer wall of the shell.
extinct ocean-dwelling invertebrates with coiled shells, classified in the same group as squid and octopus in the phylum Mollusca.
