1. An extinct marine animal from the Paleozoic Era, known from fossilized remains that resemble writing or marks on rock.
Usage: paleontology; geology

Examples

• Graptolites are important index fossils used by geologists to date rock layers.
• The name graptolite comes from Greek words meaning 'written stone' because of their appearance.
• Scientists study graptolite fossils to understand ancient ocean environments.
• Graptolites lived in colonies and floated in Paleozoic seas.
• The discovery of graptolite remains helped establish the geological timescale.