Fossil (fossil) The remains, relics and remains of ancient organisms preserved in rock formations. The word fossil comes from the Latin word fossillis, which means to dig. Fossils are the main research object of paleontology, which provide evidence for studying the life history of animals and plants during geological periods. There have long been records of fossils in ancient Chinese books. For example, Ji Ran in the Spring and Autumn Period and Wu Jin in the Three Kingdoms Period both mentioned the "dragon bones" produced in Shanxi Province. "Dragon bones" are the fossils of bones and teeth of ancient vertebrates; "Mountains and Seas" The Classics also contains descriptions of "stone fish" (i.e. fish fossils); Tao Hongjing of the Qi-Liang Dynasty in the Southern Dynasty has a description of ancient insects in amber; Shen Kuo of the Song Dynasty has a correct understanding of the origin of snail fossils and Du Wan of fish fossils. So far, the earliest bacterial fossils discovered are filamentous bacterial fossils from the Wallawona Group in Australia 3.5 billion years ago.
Only a small part of the organisms that formed the geological period are suitable for the geological environment and have been preserved as fossils: ① The organisms themselves must have certain hard bodies, such as invertebrate shells, carapace, and vertebrae Animal bones, teeth, plant trunks, leaves, spores, pollen, etc.; ② After the death of organisms, they must be quickly buried in sediments to avoid damage by biological, mechanical or chemical effects; ③ They must undergo various processes over a long period of time petrification. If biological remains are buried in situ, it is easier to form complete fossils. For example, there are a large number of well-preserved animal and plant fossils in the Late Tertiary Miocene Shanwang Formation in Linqu, Shandong, China. Another situation is that the remains of organisms after death may have undergone various transportation effects. These fossils buried in other places generally have varying degrees of damage, are well sorted, and sometimes have directional arrangements. The discipline that studies the remains of living things, the burial of remains, and the formation process of fossils is called taphonomy.
Preservation types Fossil preservation types can generally be divided into solid fossils, cast fossils, trace fossils and chemical fossils. ①Solid fossils refer to fossils in which the remains of ancient organisms have been preserved in whole or in part. For example, insect fossils in amber in the Tertiary coal seams in Fushun, China, are preserved under strict sealing conditions. The mammoths in the permafrost of the Quaternary Ice Age in Siberia were preserved as a whole under severe freezing conditions. But most fossils can only preserve the hard parts of organisms, and they have undergone obvious changes, that is, petrification. With chitin, chitin-protein or easily volatile components (oxygen, hydrogen, nitrogen) in protein skeletons disappear through the action of ascent, leaving only a carbonaceous film, so it is also called carbonization, such as graptolite and plant leaves. Preserved by carbonization. When some of the components of biological hardware are dissolved by groundwater and replaced by foreign minerals, the fine structure of the original hardware can be preserved, which is called metasomatism. For example, in petrified wood, the growth rings and even the shape of plant cells can still be clearly seen. ② Cast fossils refer to the impressions and replicas left by biological remains in the substrate, surrounding rocks, and filling materials. According to the relationship between fossils and their surrounding rocks, they can be divided into several types, such as impression fossils, impression fossils, cast fossils and replica fossils. ③ Trace fossils refer to the traces and relics left on the surface or inside the sediments during ancient biological activities, such as vertebrate footprint fossils, vermiform crawling fossils, and animal excrement coprolite or egg fossils. . Trace fossils in a broad sense also include labor tools and cultural relics of ancient humans in the Paleoancient Age. ④Chemical fossils refer to the fact that although the remains of ancient organisms have not been preserved, the organic components that make up the organisms are decomposed to form various organic compounds such as amino acids and fatty acids, which can still be retained in the rock formations, which is enough to prove the existence of ancient organisms. Such fossils are called chemical fossils.
Research significance From the end of the 18th century to the beginning of the 19th century, the British W. Smith established the fossil sequence law based on the vertical distribution of fossils based on the stratigraphic sequence. This not only uses fossils to determine the age of strata, but also provides evidence for biological evolution. Paleontologists have found that the higher the stratigraphic layer, the more types of fossils it contains, and the more complex the morphological structures of the fossils are, reflecting the evolutionary law of biological types from few to many, morphological structures from simple to complex, and from low-level to advanced.
Paleoecological research on biological fossils is an important basis for reconstructing paleogeography and paleoclimate in geohistorical periods. Every living thing is the result of living in a certain environment and adapting to the environment. Various organisms have characteristics that reflect environmental conditions in their behaviors and body structures. These characteristics can be used to infer the living environment of organisms. For example, marine fossil corals and foraminifera reflect the marine environment; terrestrial plant leaves, roots, insects, etc. reflect the continental environment. Based on the study of the living environment and climate conditions of various biological fossils in a geological period, it is possible to infer the distribution of sea and land, the location of coastlines, and the extent of lakes, rivers, and swamps in that period. The reconstruction of paleoenvironment and paleoclimate is very important to the understanding of geological history. In addition, the hard parts of organisms can also form rock signs that reflect the ancient environment and climate. For example, shell rocks reflect the coastal environment, biological reefs reflect the low-latitude warm sea environment, and peat or coal reflects the humid swamp environment.
The large collection of fossil data also provides the basis for the systematic classification of paleontology. Modern organisms were developed from ancient organisms over a long geological period. There are varying degrees of affinities between various organisms, thus establishing a natural classification system that reflects the affinities and evolutionary development of the biological world.
The fossil groups of ancient organisms are the same as modern organisms. They are generally divided into two categories: low-level prokaryotes and advanced eukaryotes. There are 5 kingdoms, namely, prokaryotes, protists, and Kingdom Fungi, Kingdom Planta and Kingdom Animalia are divided into phylum, class, order, family, genus, species and other units.
Because organisms developed from low-level to advanced to modern times, the biological categories in each period of geological history are different, and the fossil groups in each period are related to the biological categories at that time. Different geohistorical periods have their developed biological categories, and also have their own characteristic fossil groups. Some categories dominate during this period, while some categories decline or become extinct during this period. In short, the changes in biological categories and fossil groups over time show the systematic development history of biological evolution.