Fossils are biological remnants or relics of previous geologic times preserved in rock strata. Biological remains are usually the hard parts or prints of organisms. However, under cold and sealed environmental conditions, complete biological remains may be well preserved. In addition to the biological body, fossils also include traces of living organisms, moulds formed during the fossilisation process and the residual organic parts. Fossils can indicate the existence of ancient organisms and are the main focus of palaeontology. Based on their size, fossils are divided into large fossils, microfossils, and supermicrofossils. Based on the biological classification, fossils can also be divided into animal fossils, plant fossils, vertebrate fossils and fish fossils. Fossils are the important basis for studying biological evolution, determining stratigraphic ages, and evaluating palaeogeographic and palaeoclimatic environments.