Orthoceras swam in many of the world's seas approximately 470 to 360 million years ago. Their modern counterparts are squid, octopus and cuttlefish. The word orthoceras means 'straight horn', referring to the characteristic long, straight, conical body. Although not curled like most ammonites, othoceras shared a similar internal structure of many chambers separated by walls, called septa. The soft body parts were contained in the open ended segment. These sea creatures are thought to have fed on plankton and small shelled species, grabbed by the tentacles.

Movement was dependant on the many chambered body - the animal could squirt water from its rear end to propel it forwards. By adding or removing fluid from the chambers (via the long connecting tube, the siphuncle) the animal could adjust its buoyancy and thereby swim at different depths. the siphuncle and septa lines are often clearly visible on orthaceras fossils. Sizes of these animals varied from a few centimetres in length to stunning specimens of several meters. After death, the bodies would settle on the sea floor, often currents would gradually align many in one direction as sediments started to cover them. Othoceras fossil beds, for example in Morocco, show that these areas were either once under the sea or have been raised by continental plate movements (or both!).

The name Pegoda Stone, which they are sometimes know by, arose due to the (slight) resemblance to Chinese Temples.