Fossil range: Ordovician – Triassic, Silurian.

Age: Silurian - 400 Million years old.

Size: Orthoceras ranged in size from a few centimetres to over 8 metres long.


Orthoceras were one of the earliest and most successful sea living predators. Their bodies were constituted of a sharp beak and tentacles similar in design to modern cuttlefish and squid. They lived in the front chamber of their shells. Their only distant surviving relative today is the Nautilus which occurs in the Indian Ocean.

They are a type of extinct nautiloid. Their fossil remains are common and can be found throughout the world. Particularly in limestone rich area’s where on occasion their fossil remains literally constitute the rock. One explanation scientists have suggested to explain why Orthoceras can be found fossilised in such vast numbers so closely together is that this was an early manifestation of the post mating mass deaths which are still commonly replicated by some modern Cephalopods. Dating from so long ago, perhaps the greatest abstract wonder that Orthoceras represent is that life really is older than many of the rocks and crystals which surround us today upon the earth.