Onius

Onius is a genus of extinct cephalopods belonging to the subclass Nautiloidea. These marine invertebrates lived during the Devonian period, approximately 419.2 to 358.9 million years ago. The genus Onius is characterized by its nautiliform shell, which is typically coiled and has a visible siphuncle. The siphuncle is a tube that runs through the camerae (chambers) of the shell and was used by the nautiloid to regulate buoyancy by adjusting the amount of gas or liquid within the chambers.

Fossils of Onius have been found in various parts of the world, indicating a widespread distribution during the Devonian. The shell morphology of Onius, like other nautiloids, suggests a nektonic lifestyle, meaning they were actively swimming organisms rather than sessile bottom-dwellers. Their diet likely consisted of small invertebrates, and they were prey for larger marine predators.

The study of Onius and other Devonian cephalopods provides valuable insights into the evolution of mollusks and the ancient marine ecosystems of that era. While not as diverse as ammonoids or modern cephalopods, nautiloids like Onius represent an important branch in the cephalopod evolutionary tree. The genus contributes to our understanding of Paleozoic marine life and the diversification of cephalopods before the rise of the ammonites.