Paleontology, a subdiscipline of geology, is the intersection of life sciences and earth sciences. It is not only a unique branch of the life science with a historical and scientific nature, an important foundation and component of historical biology such as the origin of life, the history of development, the macroevolutionary evolution model of organisms, rhythm and mechanism of action, etc.; it is also a branch of earth science, which studies the biological remains, relics and fossils preserved in the strata, in order to determine the order and era of the strata, understand the history of crustal development, and infer the distribution of land and water, climate change and the formation and distribution of sedimentary minerals in geological history.
In the last issue, I promised everyone that this time I would like to talk about paleontology, in fact, I only studied for one semester, but between "interlaced like mountains", there are still some things that can be taken out to show off, and I want to share with you the paleontology that laymen do not know.
I remember a few days ago, in the "China Geological Salon" group, everyone discussed the authenticity of a trilobite fossil, which completely pulled me back to the paleontology class 11 years ago.
"What's that on the chalkboard?" I don't know anyone. "Stupid you, that's Russian..." Teacher Chen wrote a bunch of Russians on the blackboard for a short while, including ammonites, trilobites, etc., different doors, programs, and eyes, with different names. Then each of us saw some cards about the various ammonites and trilobites, and the moment I saw the ammonites, it felt like they were really beautiful.
Ammonite, the name comes from the pictographic meaning of the horn of the ancient Greek god Amun, which is also called the horn stone in many places. Ammonites have been closely related to various legends for thousands of years, from the horn of the god Amun in ancient Egypt to the god Vishnu in ancient India, to the medieval St. John's snake stone and the German bedside ammonite, from snow-capped Siberia to the lush Amazon rainforest The legend of ammonite has been a story that all ethnic groups have been talking about.
Ammonite is a subclass of the mollusk phylloscopiaceae. Ammonites are not living animals but extinct marine invertebrates that lived from the Devonian to the Cretaceous. It first appeared in the early Devonian Period of the Paleozoic Era (about 400 million years ago) and flourished in the Mesozoic Era (about 225 million years ago). Therefore, strictly speaking, when mentioning ammonite, there is no need to add the word fossil, because this category is fossil, and the statement "ammonite fossil" is semantic repetition, just like saying "paleontological fossil", which is incorrect.
Phylum: Mollusc phylum Mollusca
Order: Cephalopoda cephalopoda
Suborder: Ammonoidea
There are four suborders under the cephalopods, of which octopus, squid, and cuttlefish all belong to the suborder Slugs, nautilus belongs to the subclass Nautilus (it is a living fossil, more on that later), the suborder Phylloscopus (extinct, to be talked about later), and the ammonite subclass we want to talk about today.
It is said that the evolutionary history of ammonite has experienced four mass extinctions in geological history, each time evolving from a simple and smooth shell to complex and shell decoration and morphology, and the soft part of the ammonite shell and the life history of ammonite have long been a mystery that scientists dream of solving due to the lack of fossil evidence. According to the latest research, ammonites may be benthic animals, feeding on small crustaceans, and perhaps the fundamental factor that led to the extinction of ammonites at the end of the Cretaceous period is hidden in the latest evidence, which makes me, a student who has studied paleontology, feel very much looking forward to it.
In paleontology, the most controversial is the trilobite. Many fossils can now be artificially crafted, but they can't escape the fire-eyed crystals of experts. Some edges and edges can be recognized at a glance. However, when I heard Professor S of Peking University say that the Department of Paleontology of Peking University had recruited a student for several years, I was very sorry.
Trilobite ( scientific name : trilobite ) is an animal in the extinct trilobite family of arthropod phylum. They first appeared in the Cambrian Period, peaked in the early Paleozoic Era, and gradually reduced to extinction. The latest trilobites disappeared from the extinction of biological swarms at the end of the Permian 250 million years ago. Trilobites are very well-known fossil animals, and their popularity may be second only to that of dinosaurs. Of all the fossil animals, trilobites are the most abundant, with nine (or ten) orders and more than fifteen thousand species that have been identified so far. Most trilobites are relatively simple, small marine animals that crawl on the ocean floor and absorb nutrients by filtering sediment. Their bodies are segmented with grooves that divide the body into three vertical leaves.
The world of trilobites
christen
As early as 300 years ago, during the Chongzhen period of the Ming Dynasty, a man named Zhang Huadong found a "monster" buried in stone in Dawenkou, Tai'an, Shandong, whose appearance resembled bat spreading its wings, so he named it "Bat Stone". In the 1920s, China's paleontologists conducted scientific research on the "bat stone" and finally figured out that it was the tail of a trilobite. This trilobite lived 500 million years ago in the late Cambrian period and is an arthropod in the ocean. In order to commemorate the first name given to the trilobite in the world, Chinese scientists have translated this trilobite from the Latin name to Chinese the name is still called batworm. The earliest records of foreign research on trilobites can be traced back to 1698. At the time, Ruud named a fossil trilobite with three round tumors on its head the "triomatous worm." By 1771, Walchi gave an appropriate name to the animal according to its morphological characteristics, that is, the body could be divided into three parts from both vertical and horizontal aspects: the head, thorax and tail in the longitudinal direction, and the lateral part of the central axis and its flanks laterally, thus giving an appropriate name - "trilobite".
reproduction
Trilobites were first introduced with the small shell fauna of the early Cambrian period, the small shell fauna mainly refers to the soft tongue snail, gastropods, veneers, beaked shells and a large number of individuals with unknown classification position (generally only 1 to 2 mm), low mollusks, the marine conditions at that time have been suitable for their survival, these animals have brought a rich food source to the trilobites, in the ocean at that time, trilobites have not yet encountered strong competitors, so they run amok and develop rapidly, The whole Cambrian became the world of trilobites.
body
Trilobites have a peculiar appearance, and their bodies are divided into three parts: head, chest and abdomen. The shell has three leaf bodies, and the two lobes are located on each side of the longitudinal axis leaves, hence the name : " trilobites " . Trilobites are slightly ovate or oval in shape from the back, and the adults are 3 to 10 cm long and 1 to 3 cm wide. The shell is hard, protruding in the middle, the two ribs are low and flat, and it also forms three parts of the longitudinal column, which is how the name trilobite comes from. Because the back shell of the trilobite is hard, it is easy to be preserved as a fossil. We know today about this extinct animal, and we know them all through fossils. The head of the trilobite can be called the head because of the hard armor, the central bulge on the head carapace is called the head saddle, the shape and size of the head saddle vary greatly in different species, and the front part of the head saddle is the head cap, on which the eye ridge, eye lobes and eyes are developed. The edges on both sides of the head cap are concave and extend to form a movable cheek, which often further forms a very sharp buccal spine that extends to the back of the body, and the entire cephalosa is an important basis for trilobite classification and species identification.
Tail of the breastplate
The pectoral carapace consists of a number of similarly shaped thoracic segments that are connected to each other and are similar to the solitary segments of most arthropods, which can be moved and have a curved function. Trilobites are able to curl up or stretch out all over these active thoracic segments, but juvenile trilobites do not have thoracic segments. The caudal carapace refers to the part of the body of the trilobite that is formed by the fusion of several body segments, which form the unique tail of the trilobite. The tail of the trilobite is generally semi-circular, and because the edges of the tail often form tail spines of different sizes, the tail of many trilobites stretches and radiates, becoming very beautiful. The entire back of the trilobite is hard and smooth, but scientists have found that some species have small tumors or small nodules on the dorsal carapace, which, together with the cheek spines, rib spines, and tail spines on the dorsal carapace, form a complex protective "armor."
Development
After years of research by paleontologists from various countries, it is believed that trilobites have complex stages of development. Trilobites are hermaphrodites, oviparous, and in their lifetime development, they have to go through multiple molts to grow, and many current arthropods have inherited the growth mode of trilobites. Trilobites generally go through three growth stages from larval to adult, namely juvenile, segmented and adult. Understanding this, it is necessary for us to collect trilobite fossils in the wild, if people have a little knowledge about the development stage of trilobites, they can make a general identification of the collected trilobites fossils, so as not to treat the same trilobite at different stages of development as different forms of genera.
In addition to the small body, the juvenile trilobites often have prominent bulges, the head and tail are not distinguished, there is no thoracic segment, and the insect body is spherical. Later, as the trilobites continue to grow, the thoracic node gradually increases, and when the thoracic nodes all grow up and no longer increase, they enter adulthood, which means that the trilobites have reached the stage of sexual maturity and can have children. Every time a trilobite molts its shell, its body enlarges, as does the number of segments of the spines, tumors, and even tail nails on the shell.
Trilobites can grow up to live carefree in the ocean, and so far, no trilobite fossils have been found in the continental strata, which shows that this animal really only lives in the ocean. Because trilobites fossils often appear with corals, brachiopods, and cephalopods, it suggests that they all prefer to live in warmer shallow seas, where trilobites feed on a variety of tiny creatures, or are also interested in seagrass and animal carcasses. To be sure, they do not have the ability to actively attack, because trilobites do not have good swimming organs, nor do they have a streamlined body shape, and travel slowly in the water. It is conceivable from their strong dorsal armor that once a ferocious animal (such as a nautilus) poses an attack on them, the trilobite will quickly curl up its body, protect itself like a pangolin, and quietly sink to the bottom of the sea.
Why are there so many trilobites?
Why did so many trilobites appear during the Cambrian period? Scientists believe through paleoecological research that trilobites have a good way of living adapted to the environment. Trilobites do not follow a single mode of life, some species of trilobites like to swim, some species like to float on the surface of the water, some like to crawl on the bottom of the sea, and some are accustomed to living in the sediment, they occupy different ecological spaces, cambrian oceans have become the world of trilobite fossil leaf insects. In the geological epoch after the Cambrian Period, this unusual creature coexisted with other invertebrates for a long time before gradually decreasing and declining. China's trilobite fossils are very rich, only in the early Cambrian period found more than 200 genera, Shandong Tai'an rich "swallow stone", after research found that is a large number of active trilobites at that time after the death of the accumulation of formation, those exposed on the surface of the rock are flying "swallow", in fact, is a long long tail thorn trilobite tail beetle.
After the emergence of trilobites, it was used as a representative of many organisms throughout the Early Paleozoic Era (including the Cambrian, Ordovician and Silurian), and together with many other creatures, they opened the prelude to the earth's biological diversification, and since then, a thriving biological world has truly emerged. The population of trilobites in the Late Paleozoic period decreased with the emergence of a large number of marine invertebrates with a large number of phyla, and finally disappeared when the Mesozoic era arrived.
Animal classification
In animal taxonomy , trilobites belong to the phylum arthropods , trilobites. They lived in ancient oceans, occurring mainly in the Cambrian period and reaching their apex by the late Cambrian period. Since then, trilobites have gone from the peak of their peak to decline, and continued to extinction at the end of the Permian, without entering the Mesozoic Era. Trilobites have grown endlessly throughout the long geological process of more than 300 million years in the Paleozoic Era, and have bred a large number of taxa and a huge number, totaling more than 1500 genera and more than 10,000 species, of which about 500 genera are found in China.
Trilobites are mostly ovoid or oval in shape, and individual sizes vary widely. Found in the Ordovician strata of Portugal, Ula rift is one of the largest trilobites, up to 70 cm long. Tiny trilobites such as paleocarp and bulbous spheroids are less than 6 mm. Common trilobites are generally 3 to 10 cm long and 1 to 3 cm wide. More than 20 centimeters is considered large. In the early Cambrian strata of Kunming, China, a 30 cm length of Lederliji worm was found.
Although the age of the trilobite is far away, scientists have a good understanding of its morphology, structure and other characteristics, the main reasons are as follows: First, the trilobite body surface is covered with a solid carapace, in the process of ontology to undergo many shelling growth, so they leave more fossils in the formation than other organisms; Second, few larger and more ferocious animals in the Cambrian oceans live with it than trilobites, so they are able to multiply rapidly and spread widely; In addition, trilobite fossils are mostly preserved in fine-grained limestone or shale, so not only can the characteristics of the shell be clearly observed, but sometimes its internal structure can also be seen very clearly.
The main feature of the trilobite is the structure of its dorsal shell, which has a protruding "head saddle" in the center of its head, which may be the place where the brain is placed. The surface of the saddle is either smooth and unadorned, some dotted with nodules, and some with a large number of transverse grooves. These transverse grooves are called "head saddle grooves". On both sides of the saddle of the head, there are generally pairs of eyes. There is a groove along the front and back of the eye, called the "surface line", which is where the trilobite grows and burrows out of the body. The anterior end of the ventral surface of the head has a pair of segmented tentacles, which are both acting organs and sensory organs. Behind the tentacles is the feeding mouth, usually covered with a "lip flap". On both sides of the mouth there are many small and segmented organs of action - appendages, and the appendages have fine cilia on them, which can probably play a role in breathing.
The thoracic segments of trilobites are as many as a dozen and the few are divided into only two segments. Sections are interrelated in the form of tiles (i.e., one piece is overlaid on top of another like a roof tile) to facilitate curling. Trilobites have numerous segmented appendages on both sides of the ventral surface, with cilia on the appendages, so these appendages are also used for movement and breathing. The tail of the trilobite is the same as the thorax, and is longitudinally divided into the central axis and the ribs on both sides, and its morphology is diverse; The edges of the tail are either prickly or unscathed.
Since the emergence of trilobites in the early Cambrian period, the main structural characteristics of each part of the entire phylogenetic evolution have gradually changed accordingly, and these changes mainly have the following aspects:
1. Changes in the morphology of the head saddle: the head saddle morphology of the primitive trilobite in the early Cambrian period is mostly oblong-conical, and the bulge is not significant. Later, after the middle Cambrian period, the head saddle gradually shortened, and the sides tended to be parallel, becoming cylindrical, and some even became spherical. By the late Cambrian period and beyond, even the boundary between the head saddle and the cheek parts on both sides was unclear.
2. Change in the position of the posterior branch of the surface line: the end point of the posterior branch of the surface line (that is, the section of the surface line after the eye) of the early trilobite often intersects with the posterior edge of the head or the cheek angle; Later, after the Ordovician, they often intersected on the lateral margins of the head.
3. Eye changes: the eyes of some trilobites. In the early days it was crescent-shaped, then gradually became smaller and finally disappeared. Another type of trilobite with more developed compound eyes, the eyes change from small to large, and finally the stalk will appear, and the eye will grow on the top of the towering stalk. Many trilobites of the Silurian fall into this category.
4. Changes in long spines around the body: Cambrian and Ordovician trilobites rarely have long spines, while the Type Long Spines of the Silurian Period and later are more common, and the spines are more complex than before.
5. The trend of thoracic joints from more to less, tail from small to large, transverse grooves on the head saddle from more to less, etc. are also shown in many types of trilobites.
Some people say that I work to make money; some people say that I work to make a living. If this job costs me my life or even not enough, why should I do it? Because of this, many people have chosen to change careers. Those who can persevere also think that they have put a lot of hard work into it.
I am glad that I was able to see such beautiful fossils in the university classroom and receive such a good education. Perhaps for some, college is just a stepping stone to the door of work. But in my opinion, it has allowed me to gain not only scarce geological knowledge, but also a lot of teachers and classmates with perseverance, courage, perseverance and dreams. It is because they are scattered in all corners of the motherland and doing similar and repetitive work that the geological industry will be passed down from generation to generation like culture and art.
Which profession, which industry, has its own bitterness and tiredness, and also has an exit that is difficult to break through, but the phrase "three stinky cobblers raced Zhuge Liang" will never be empty. Everyone's life is in the process of continuous learning and continuous efforts, rather than just relying on a paper diploma to determine a lifetime.
No one has the right to measure the lives of others by their own standards, and I only hope that through my own modest efforts, more people will fall in love with geology and professional disciplines will not be marginalized.