Authentic fossilized Araneograptus murrayi graptolites, 2.5 cm length, 480 million years old, Ordovician, Morocco

Description

Graptolites were colonial marine animals that lived in colonies made up of an interconnected system of tubes. They lived between the Cambrian and Carboniferous periods, from about 520 million years ago to about 350 million years ago.

The first graptolites lived on the sea floor, attached to boulders or forming vertical cones rooted in soft mud. This is still the lifestyle of the living relatives of graptolites. At the beginning of the Ordovician period, graptolites became buoyant. They were among the first animals to colonize the open sea and were able to exploit the enormous untapped reserves of food (single-celled organisms) in the upper layers of the oceans. Various species quickly evolved to exploit these reserves of food and in response to the new challenge of a floating life.

Graptolite fossils appear as thin, often shiny marks on rock surfaces that look like pencil marks, and their name comes from the Greek for "writing in rocks." They are the remains of intricate colonies, some of which housed up to 5,000 individual animals; these individuals lived in a collagen skeleton, similar to the material that human fingernails are made of.