When the Devonian period dawned about 416 million years ago the planet was changing its appearance. The great supercontinent of Gondwana was headed steadily northward, away from the South Pole, and a second supercontinent began to form that straddled the Equator. Known as Euramerica, or Laurussia, it was created by the coming together of parts of North America, northern Europe, Russia, and Greenland.
Red-colored sediments, generated when North America collided with Europe, give the Devonian its name, as these distinguishing rocks were first studied in Devon, England.
The Devonian, part of the Paleozoic era, is otherwise known as the Age of Fishes, as it spawned a remarkable variety of fish.
The fossils commonly known as orthoceras are extinct 'straight-shelled' cephalopods that lived during the Upper Devonian period around 370 million years ago. They lived inside their shell, had tentacles they could use to grab food and used jet propulsion, squirting water to move. The rock containing them is quarried from the Atlas Mountains of Morocco and polished to make decorative items with the fossils visible on the polished surface.
While they lived orthoceras was an extremely common animal and they probably made up the majority of the biomass in the oceans. Orthoceras were one of the dominant orders of their time and as a result ranged widely in size. The smallest were less than an inch (2.5cm) long and one species grew to 14 feet
Unlike a hermit crab who must find and move into a bigger shell, an orthoceras didn't have to go anywhere. It simply grew its shell bigger. It did this by creating a new dividing wall inside the shell called a septa. Today, you can see the septa separated by lines in the fossil. Scientists can tell the age of the orthoceras by looking at how many lines there are.
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