Only a small part of the organisms that formed the conditional geological historical period adapted to the geological environment and were preserved as fossils: ① The organisms themselves must have certain hardware, such as shells and carapace of invertebrates, bones and teeth of vertebrates, trunks, leaves, spores and pollen of plants; (2) After the death of organisms, they must be quickly buried by sediments to avoid being destroyed by biological, mechanical or chemical actions; (3) It must undergo various petrochemical actions for a long time. If the biological remains are buried in situ, it is easier to form complete fossils, such as a large number of complete animal and plant fossils preserved in Miocene Shanwang Formation in Linqu, Shandong, China. On the other hand, the dead bodies of living things may be subjected to various treatments. These fossils buried in different places are generally damaged to varying degrees, with good sorting degree and sometimes directional arrangement. The discipline that studies the burial of biological remains and remains and the formation process of fossils is called burials.
Preservation types Fossil preservation types can generally be divided into solid fossils, die-casting fossils, trace fossils and chemical fossils. (1) Entity fossils refer to fossils that have preserved all or part of the remains of paleontology, such as insect fossils in tertiary coal amber in Fushun, China, which are preserved under closed conditions. Mammoths in Siberia's frozen soil during the Quaternary Glacial Period were completely preserved under severe cold and freezing conditions. However, most fossils can only preserve the hard parts of organisms, and have undergone obvious changes, that is, fossilization. Volatile components (oxygen, hydrogen and nitrogen) in chitin, chitosan-protein or protein's bones disappear by rising and falling, leaving only a layer of carbonaceous film, also called carbonization. For example, graptolites and plant leaves are preserved by carbonization. The components of biological hardware are partially dissolved by groundwater and replaced by foreign minerals, which can retain the fine structure of the original hardware, called metasomatism, such as silicified wood, whose annual rings and even the shape of plant cells can still be clearly seen. ② Die-casting fossils refer to the impressions and recasts left by biological remains in the substrate, surrounding rocks and fillers. According to the relationship between fossils and their surrounding rocks, they can be divided into imprint fossils, impression fossils, mold fossils and multiple fossils. (3) Trace fossils refer to the traces and remains left by ancient organisms on the surface or in sediments during their life activities, such as footprint fossils of vertebrates, reptile fossils and animal excrement or egg fossils. In a broad sense, trace fossils also include the labor tools and cultural relics of the ancients in the era of old artifacts. (4) Chemical fossils mean that although the remains of ancient creatures have not been preserved, the organic components that make up the creatures are decomposed into various organic substances such as amino acids and fatty acids, which can still remain in rocks, which is enough to prove the existence of ancient creatures. This kind of fossil is called chemical fossil.
Research Significance From the end of 18 to the beginning of 19, W Smith of Britain established the law of fossil sequence according to the vertical distribution of fossils. This not only determines the stratigraphic age by using fossils, but also provides evidence for biological evolution. Paleontologists have found that the higher the stratigraphic level, the more fossil categories it contains, and the more complex the morphological structure of fossils, reflecting the evolution law of biological categories from less to more, morphological structure from simple to complex, and from low to high.
The paleoecological study of biological fossils is an important basis for reconstructing geological history, paleogeography and paleoclimate. Every living thing is the result of living in a certain environment and adapting to it. The habits, behaviors and body shapes of all kinds of creatures have the characteristics of reflecting environmental conditions. Using these characteristics, we can infer the living environment of organisms, such as marine fossils, corals, foraminifera and so on. The leaves, roots and insects of terrestrial plants reflect the continental environment. According to the study of the living environment and climatic conditions of various biological fossils in a geological period, we can infer the land and sea distribution, coastline position and the scope of lakes, rivers and swamps in that period. The reconstruction of paleoenvironment and paleoclimate is very important for understanding geological history. In addition, the hard parts of organisms can also form rock marks reflecting the paleoenvironment and paleoclimate, such as shell rocks reflecting the coastal environment, reefs reflecting the warm sea environment at low latitudes, peat or coal reflecting the wet swamp environment, and so on.
The collection of a large number of fossil data also provides a basis for the systematic classification of paleontology. Modern organisms developed from ancient organisms through a long geological period, and there are different degrees of kinship among various organisms, thus establishing a natural classification system that reflects the kinship and evolution of the biological world.
Like modern organisms, fossils are generally divided into two categories: lower prokaryotes and higher eukaryotes. * * There are five realms, namely, kingdom, protozoa, fungi, plants and animals, and below them are phylum, class, order, family, genus and species.
Because organisms have developed from low-level to advanced and then to modern times, the biological categories in different periods in geological history are different, and the fossil groups in each period are related to the biological categories at that time. Different geological periods have their developed biota, and biota also have their own characteristic fossil groups. Some groups dominated during this period, while others declined or became extinct during this period. In a word, according to the process of time, the changes of biological species and fossil groups show the systematic development history of biological evolution.