Cephalopod nautiloids date back to the Early Ordovician Period almost 500 mya and survived to the Late Triassic about 230 mya. Some believe they even survived through the Cretaceous Period about 150 mya. Wow! Their fossilized shells have been discovered all around the world in large assemblages and commonly occur in marine rock, especially lime stone .
The straight shelled nautiloids were closely related to the ammonites which evolved spiraled shells. But due to their long linear shells and a weak muscle, they probably weren’t as agile. They moved about the same way, though, with the use of a siphuncle tube that runs the entire length of the shell through each of its inner chambers. Once filled with water, the cephalopod nautiloid could force the water out, propelling itself backward with a kind of jet propulsion. By releasing the water and leaving air space, the tube could serve as a buoyancy device allowing the animal to rise and lower itself to different depths.
Their fossils have been quarried by Europeans for many years and adorn floors, stairs, jewelry, gravestones and more with their durable and desirable beauty.
The Orthoceras nautidoids display extreme diversity in size from a few inches to 14 feet in length. One of the largest cephalopod nautiloid giants from the earliest years, Cameroceras, reached 30 feet in length.
Phylum: Mollusk (large diverse group of invertebrates with soft bodies encased in a shell i.e. clams, snails, oysters )
Class: Cephalopoda (means prominent head and tentacles i. e. squid, octopus, nautilus, cuttlefish)
Subclass: Nautiloidea (series of chambers of increasing size connected by a central tube)
Order: Orthocerida (extinct group of cephalopods possessing long straight shells)
Genus: Orthoceras (means straight horn)