Orthoceras (“straight horn”) is an extinct squid-like mollusk from the Ordovician period, about 450 million years ago. The creature lived in the last open segment on the wide end of the shell, and ranged from 1 cm to 6 ft long. As the body outgrew the segment, a dividing wall, called the septa, grew to separate the old home segment from the new. A small tube, the siphuncle, runs down the center of the shell and was used for propulsion and buoyancy. These fossils are found in the Atlas Mountains of the Sahara Desert in Morocco.
60 – 500 million years old, ammonites are an extinct form of mollusk related to the octopus and chambered nautilus. Like the nautilus, it had a hard shell with a distinctive spiral pattern. Ammonites range in size from 1 mm to over 2 feet, and vary in the type of mineral replacement during fossilization. The name comes from its resemblance to a ram’s horn: in Egyptian mythology, the God Ammon looked like a man with horns like a ram. Ammonites are found in Canada, Europe, Madagascar, Peru, and Morocco.