Definitions for "Graptolite"
One of numerous species of slender and delicate fossils, of the genus Graptolites and allied genera, found in the Silurian rocks. They belong to an extinct group (Graptolithina) supposed to be hydroids.
"writing on rock". An extinct group of marine organisms. They appeared in the Cambrian period (c.520 Ma) and became extinct between the Permian and Triassic periods, 248 million years ago. They are found all over the world and evolved very quickly – this means they are important for dating rock sequences.
Graptolites were a group of extinct marine colonial animals, most of which lived attached to the sea bed. Graptolites lived from the Cambrian period (roughly 540 to 505 million years ago) to the early to mid-Carboniferous (360 to 320 million years ago). These small sea animals had a soft body, tentacles, and a hard outer chitonous covering (similar to our fingernails); they were bilaterally symmetrical. These widespread fossils are often used as index fossils. Classification: Hemichordata (chordates lacking a backbone)