Paleontological fossils "written" on rocks

Ancient organisms are creatures that lived in ancient times and are now extinct. Paleontology is a specialized science that studies paleontology, and some geological universities have related majors (for example, Northwest University, China University of Geosciences, Institute of Paleontology of Chinese Academy of Sciences, Peking University, etc.); This discipline is different from archaeological research in that it is mostly concerned with organisms and life phenomena before the emergence of human society. Paleontologists have another joke that neatly differentiates the two: We don't dig graves!

Paleontologists usually focus on two areas: the origin and evolution of life, which is the study of how life on Earth came from nothing and developed to the present day (for example, who was the first human ancestor; How living things evolved to the present day; What happens in the process of evolution, etc.); Second, biological fossils are preserved in strata successively, according to the law that species do not reappear after extinction (in other words: organisms from lower to higher, from simple to complex, there is a spiral evolution, but never an animal is determined to be extinct, and it appears again after a few years), thus giving rise to biostratigraphy. Paleontologists see the same type or species of organisms found in different strata of the world as isochronous in geological history (of course, the time required for animal dispersal, tens of thousands of years or more, is negligible for geological time measured in millions of years). The selected paleontologists that can be compared are often widely distributed, rapidly evolving and rapidly spreading organisms in a certain region and a certain geological history period. Graptolites have the characteristics of wide distribution and rapid diffusion (most graptolites belong to the floating type, which spreads quickly and is widely distributed; How many social, rapid extinction, species change frequently). Biostratigraphy provides an important basis and means for a local or even the whole world stratigraphic correlation, and paleontology is an important object of study. Graptolites are important paleontological "tools" for studying Ordovician to Silurian strata. The premise is to carry on the in-depth classification study of graptolites.

Graptolites are, as the name suggests, "like the marks of a pen on a rock "(Figure 1-2). This "trace or film" was initially thought to belong to chitin. In the 1960s, scientists showed that the graptolid bone does not contain chitin, but there are a variety of amino acids such as glycine and alanine, which may come from hard protein, and the skeletal ultrastructure shown under the projection electron microscope has protein collagen. Therefore, the composition of the graptolite appears to be a non-chitin organic compound. However, this does not prevent people from studying the taxonomy of graptolites. Graptolites have been found in strata from the Cambrian to the Carboniferous period (about 500-300 million years ago). With the study and discovery of graptolites, especially in some carbonate rocks, three-dimensional morphology specimens of graptolites have been obtained through experimental treatment (most of them take acid bubbles) (Figure 3), which greatly deepens people's understanding of graptolites. With the discovery of more stereoscopic and semi-stereoscopic specimens, paleontologists gradually clarified the concept of graptolites, and some species were reconstructed (Figure 4). The graptolites we see on the rocks are actually the places where "graptolites" once "lived" (we can use the concept of modern polyps and corals, but graptolites and polyps are not the same, and there are no animals to refer to).

Graptolites (also called graptolites) are a group of extinct invertebrates belonging to a class of hemicornithae (Graptolites). Most graptolites are social Marine creatures that live in floating camps and easily spread to all corners of the world's oceans.

After death, graptolites were rapidly buried by sediments, and were preserved in rock strata after a long period of anoxia, then underwent dehydration, compaction, and diagenesis. It appeared in Cambrian period and became extinct in late Carboniferous period. During the Ordovician and Silurian periods, graptolites evolved rapidly and were preserved in high stratigraphic richness and diversity, which provided a reliable and powerful means for finely delineating the strata in this geological history period.

The graptolite body is composed of fetal and cellular ducts (Figure 5). The cytosol is an important "unit" of the graptolite body, and it is the place where the graptolite body "resides". We usually see the graptolite body composed of the cytosol. Of course, graptolites can't be seen. Figuratively speaking, paleontologists are studying the arrangement and connections between their "little houses" and "little houses." The morphology of cell ducts is an important basis for identifying graptolites. Fetal duct is the "starting place of development" of the graptolite cell duct, which means "embryo". It is composed of primary fetal duct, subfetal duct and fetal tube spines, and is one of the main bases for the identification and classification of graptolites.

Graptolites are such "fossils written on the rock ", and there are more kinds of graptolites, which have been found and named more than 3000 kinds, and more than 2200 species have been found in China, belonging to 4 orders,31 families,202 genera.

Not only can graptolites be used for fine stratigraphic correlation as important paleontologists in the Ordovician and Silurian systems (the establishment of several global standard stratigraphical profiles - commonly known as "golden nails" - depends on graptolites), but recent studies have shown that graptolite shales (mainly black rock series preserved in large quantities by graptolites) are obvious indicators for the exploration of some shale gas. Therefore, the study of graptolites will be further studied with the development of science and technology.