Straight shelled nautiloids date back from the Early Ordovician Period roughly 500 million years ago and survived into the Late Triassic Period around 230 mya. That’s approximately 270 million years of living on earth . . . overwhelming and astounding!  Their fossilized shells have been discovered all around the world in large assemblages and commonly occur in marine limestone rock.

During the 18th and 19th centuries, all the straight shelled nautiloids were named orthoceras, creating a wastebasket taxon and confusion. It is now known that many groups of nautiloids developed a straight or slightly curved shell and are more recently referred to as orthocones.

The orthocone/orthoceras were an abundant group of straight shelled, cephalopod nautiloids during the Paleozoic timeslot and were less abundant by the end of the Triassic period. They were related to the cephalopod ammonites possessing spiraled shells, which evolved after them. The straight shelled nautiloids, likely, were not as agile as their cousin ammonites. Both species possessed a siphuncle tube that ran through each of the animal’s inner chambers the entire length of their exoskeleten shells. Each inner chamber was separated by a wall called, a septa wall. As the animal grew, it added another septa wall and a new septa chamber of a larger size.

To move throught the ocean water, the orthocone nautiloids and ammonites filled their inner chambers with water by using the siphuncle tube. Then, the cephalopod nautiloid orthocones and ammonites forced the water out, propelling themselves backward with a kind of jet propulsion. By releasing the water and leaving air space, the tube served as a buoyancy device allowing the animal to raise and lower itself through various ocean depths.

The orthocone nautiloids possessed 8 to 10 powerful tentacles which protruded from the wide opened end of its shell. The tentacles detected and captured prey. The animal had well developed eyes, a beak and a well developed head with a hood.

Nautiloid orthocone/orthoceras fossils have been quarried by Europeans for many years and adorn floors, stairs, jewelry, gravestones and more with their durable and desirable beauty.

The orthocone nautidoids displayed extreme diversity in size from a few inches to 14 feet in length. One of the largest orthocone giants from the earliest years, Cameroceras, reached 30 feet in length.

 CLASSIFICATION

Kingdom:  Animalia

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)

Family:     Orthoceridae

Genus:    Orthoceras (means straight horn)