Orthoceras was an ancient mollusk that lived more than 400 million years ago. The name means straight horn, referring to the characteristic long, straight, conical shell. The preserved shell is all that remains of this ancestor of our modern-day squid. Orthoceras were an early relative of the Ammonite and a member of the Nautiloid family. Later varieties became coiled for buoyancy unlike the straight shell of the Orthoceras which sunk more easily.