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ORTHOCERAS FOSSILS FOR SALE
These fossils, commonly known by the genus name Orthoceras, are extinct "straight-shelled" cephalopods that lived during the Upper Devonian period, around 370 million years ago. They lived inside of their shells, used tentacles to grab food, and used jet propulsion, squirting water to move. The rock containing them is quarried from the Atlas Mountains of Morocco and frequently polished to make decorative items with the fossils visible on the polished surface.
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Orthoceras: Ancient Cephalopods Of The Paleozoic Oceans
Orthoceras is a genus of extinct cephalopods closely related to modern squids, octopuses, and nautiluses. These fascinating creatures are easily recognized by their long, straight, conical shells, tentacles, and ability to propel themselves through water using jet propulsion. While their true genus is often debated, the fossils attributed to Orthoceras reveal much about life in ancient oceans.
Artists rendering of an Orthoceras. Image by Nobu Tamura Creative Commons License
Though the name "Orthoceras" is commonly used to describe many straight-shelled cephalopod fossils, most of these specimens do not belong to the Orthoceras genus itself. For example, the fossil-rich Devonian deposits of Morocco, which produce many polished Orthoceras specimens, also contain similar genera like Michelinoceras and Arionoceras. These genera look nearly identical to Orthoceras, making it challenging to differentiate them without expert knowledge.
Orthoceras had long, conical shells adorned with fine lines called lirae. The shells consisted of a series of rings, each separated by internal chambers known as septa. These chambers were filled with gas or liquid to regulate buoyancy, allowing the animal to maintain its position in the water column. The largest chamber housed the living organism, much like modern nautiluses. Equipped with tentacles, a squid-like beak, and large eyes, Orthoceras was a formidable predator. Its two modes of locomotion included crawling along the seafloor using its tentacles, akin to modern octopuses, and jet propulsion for quick movement. By expelling water through siphons, Orthoceras could propel itself efficiently through the ocean.
Orthoceras first appeared in the early Ordovician Period, approximately 488 million years ago. Their diversity peaked during the Late Ordovician through the Devonian Period, and the genus persisted until it vanished from the fossil record in the early Triassic, around 200 million years ago. During their reign, Orthoceras were among the most common marine animals, potentially accounting for a significant portion of the ocean's biomass. Their hard shells fossilized readily, leaving behind a rich legacy in the geological record.
Orthoceras occupied deep ocean ecosystems, dwelling in areas below the reach of sunlight. They likely preyed on anything they could overpower, including fish, invertebrates, and even smaller Orthoceras species. On the seafloor, they held their shells horizontally, using buoyancy adjustments to move or maintain position. The size of Orthocerida, the order to which Orthoceras belonged, varied greatly. Some species were as small as an inch (2.5 cm) in length, while others grew to an astonishing 14 feet (4.2 meters). This size range reflects their adaptability and dominance in the Paleozoic oceans.
Orthoceras fossils are often mistaken for Baculites, another straight-shelled cephalopod. However, Baculites lived during the Late Cretaceous, long after Orthoceras had gone extinct. The two can be distinguished by their shell patterns: Orthoceras exhibits simpler internal and external suture patterns, whereas Baculites' sutures are much more elaborate.
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