Graptolites are extinct marine animals that lived from the Cambrian to the Devonian periods, approximately 500 to 300 million years ago. They are primarily known from their fossilized remains, which often appear as thin, flat, and ribbon-like structures. These organisms are classified as colonial animals, meaning they lived in groups, and they are closely related to modern hemichordates. Fossils of graptolites are important for geological studies because they help scientists date rock layers and understand ancient marine environments. Their presence in sedimentary rocks can indicate specific conditions in the ocean, making them valuable for paleontology and stratigraphy.