Small shelly fossils (SSF), or small shelly fauna, are tiny fossils, many only a few millimetres long. They have a record from the latest stages of the Ediacaran to the early Cambrian period. Almost all are from earlier rocks than more familiar fossils such as trilobites. Most SSFs were preserved by being covered quickly with phosphate. This method of preservation is mainly limited to the later Ediacaran and early Cambrian periods, so the animals that made them may have arisen earlier and continued after this time.