Description
The Geisonoceras Ammonoids are extinct members of the cephalopod group of mollusks. Only a limited number of species have survived to the present day which includes the squid and the chambered nautilus. Like their younger relative Ammonites, they had a multi-chambered shell, and added more chambers as it grew, always living in the outer chamber. They thrived in the Devonian period some 400 to 350 million years ago.