Ammonites are an instinct group of marine animals. These cephalopods range in size from less than an inch to about 9 feet in diameter. They existed during the Devonian period over 300 million years ago. These ammonites are from Madagascar.
The Devonian is a geologic period and system of the Paleozoic, spanning 60 million years from the end of the Silurian, 419.2 million years ago, to the beginning of the Carboniferous, 358.9 Mya. It is named after Devon, England, where rocks from this period were first studied.