This feathered dinosaur is not considered an index fossil because it existed too long ago, and Index fossil are organic remains of animals and plants found in the strata of sedimentary rocks, and serve to date their ages. This is done through the so-called index fossils, so called because they only existed in a certain era or geological period.
These are macrophytes that grow entire in the freshwater and become fossilized by the calcification oozes, going back to the Paleozoic era about 250 million years ago.
And they are unicellular to multi-cellular organisms also found in moist terrestrial habitats.
