Graptolites

Graptolites are extinct, colonial marine creatures that lived during the Cambrian to the Devonian periods (about 500 to 350 million years ago). They are known primarily from their fossilized skeletons, which often resemble branching or finger-like structures called "colonial sifters." These organisms floated or clung to ancient sea surfaces, filtering plankton from the water for food. Their abundance and widespread presence make them important index fossils, helping geologists determine the ages of rock layers. Despite their extinction, graptolites provide valuable insights into early marine ecosystems and the evolution of early multicellular life.