THE ORTHOCERAS FOSSIL
⚡ Quick Answer
Orthoceras is an extinct, straight-shelled cephalopod that lived more than 400 million years ago during the Paleozoic era, making it a distant relative of today's squid and nautilus. Its long, cone-shaped shell fossilized in ancient seafloor sediment, and it is commonly polished today in black Moroccan limestone. Prized by collectors for its great age and clean geometric form, it is a purely natural fossil. Scroll down for what it is, how it formed, and why collectors love it.
What Is an Orthoceras Fossil?
The Orthoceras was an ancient mollusk that lived more than 400 million years ago. The name means straight horn, referring to its characteristic long, straight, conical shell. The Orthoceras shell is made up of two main segments: the siphuncle & the septa. The siphuncle is the line running down the center from head to tail. The septa are the short-curved lines that run across or side to side. The differences in composition of these shell parts allowed for differences in fossilization so the parts to be seen. These straight shelled nautiloids ranged in size from less than a centimeter to more than 14 feet! The preserved shell is all that remains of this ancestor of our modern-day squid.
How Orthoceras Fossils Formed
Orthoceras lived during the Paleozoic era, and many of the specimens sold today date to the Devonian period, roughly 400 million years ago. When these cephalopods died, their shells settled into fine seafloor sediment that slowly hardened into limestone. Over millions of years, minerals replaced the original shell material, preserving the chambered internal structure in stone. Much of the Orthoceras on the market today is quarried from black limestone in Morocco, where the pale fossils stand out in sharp contrast against the dark rock.
Why Collectors Prize Orthoceras Fossils
Because the fossilized shells are so often cut and polished, Orthoceras is popular as both a scientific specimen and a piece of natural decor. Polished plates, dishes, bookends, and towers reveal the elegant chambered form in cross-section, and no two pieces are ever exactly alike. Collectors are drawn to the combination of great age, clean geometric shape, and the striking contrast of a light fossil set into black stone.
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If these ancient cephalopods fascinate you, you may also enjoy our guides to Ammonite, Pyritized Ammonite, Crinoids, and Fish Fossils.
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