Orthoceras was an Ordovician cephalopod with a calcium carbonate shell which provided excellent physical protection against their natural predators. As the animal grew, it would seal off chambers of its shell by building internal walls called septa. The septa only had one opening, through which ran a thin tube of tissue called a siphuncle.

This necklace is an Orthoceras shell which has been fossilized into a pale gray material over a jet black base. The fossil has been hand polished to reveal the chambered septa that the animal once had, still visible 350,000,000 years later.

Each necklace is set into a fine sterling silver backing and comes with an 18" chain. Our showcase pendants have all been photographed individually and are listed by size. You can see all of them in the collection below!

The necklace comes in a decorative box and includes a small information card about the fossil. The card serves as the certificate of authenticity.

ESTIMATED AGE : c. 350,000,000 years old

Early in Earth’s history, animal life was a simple and passive thing, with most species subsisting on the flow of the ocean to carry them from one meal to the next. At the dawn of the Cambrian, all this changed when predators entered the evolutionary arms race. Swift, shrimp-like creatures and protofish found their favorite meals in early cephalopods. In response, these cephalopods would develop a brand new defense of their own: the shell. 

Shelled cephalopods developed into many subclasses including the Nautiloids, Ammonoids, and Orthoceratoids. Their calcium carbonate shells provided excellent physical protection against bites and they were able to pull themselves inside to keep their soft bodies safe. These animals made their own shells, which would grow over their lifetimes along with them. Only the front part of the shell held living tissue—older sections of their shells were sectioned off into empty sealed chambers. These chambers were a vital part of the second feature of the shell: their mobility.

Moving a heavy shell could be difficult for a soft bodied cephalopod, but an incredible solution evolved alongside the shell itself. As the animal grew, it would seal off chambers of its shell by building internal walls called septa. The septa only had one opening, through which ran a thin tube of tissue. This tube, called a siphuncle, pulled water from the empty chambers through osmosis and left them full of light gasses.

With the new density difference between the chambers and the surrounding ocean, the once heavy shell now acted like a flotation device for cephalopods and helped them stay off the seafloor. Another tube, called the hyponome, sucked in ocean water and expelled it at a high speed which caused the animals to jet around the ocean on their own, without relying on currents for motion. With these new adaptations, cephalopods were well-equipped against their former predators and some even became apex predators of their own.

These amazing shells are how we know about these animals, as they survived as detailed fossils over millions of years. Members of the Orthocerida order left behind unique fossils due to their interesting shape. Their name, which means “straight horn” in Latin, comes from the elongated, slender shapes their shells took.

What is most incredible is the level of detail still present in these polished orthoceras fossils. The septa walls are clearly visible and divide the shell’s shape and in some cases you can even see the siphuncle running through each chamber! These fossils offer a look into the deep evolutionary past and show what makes the orthoceras special.

The orthocerida were one of the first groups of cephalopods to develop shells and further generations would improve upon the design with coiling, pressure-resistant construction, and spiked surfaces. Species of orthocerida, however, did not manage to survive past the Permian. Nevertheless, their shells were a potent tool for survival and their distant cousins, nautiluses, still live in the oceans to this day.