Trilobites reached their peak 500-430 million years ago and were completely extinct in Permian 240 million years ago. It has lived on the earth for more than 320 million years, which shows that it is an extremely vital creature. In a long time, they have evolved into many species, some as long as 70 cm and some as short as 2 mm.
Chinese Name: Trilobite: Fauna: Arthropoda: Trilobite Distribution: British Columbia, new york, China and Germany. Habits: Classification, morphological structure, overview, eyes, body, tail of breastplate, living habits, development process, evolutionary history, origin, evolution, extinction, representatives of various periods, fossil preservation, formation environment, China species, research. They lived in the ancient ocean, mainly in CAMBRIAN, and reached their peak in the late CAMBRIAN. Since then, trilobites have declined from the peak to the end of Permian, and did not enter Mesozoic. Trilobites thrived in the long geological history of more than 300 million years in Paleozoic, producing countless groups and huge numbers. Trilobites can be divided into 65,438+00 orders: Coccidoidea, Grubby, Lepidoptera, Sidepoda, Scolopendra, Ctenomedusae, Fusarium, Cephalopoda and Petrognathidae. There are more than 65,438+0,500 genera and 65,438+0,000 species, of which about 500 genera are distributed in China. Overview of morphological structure Trilobites are mostly ovoid or ovoid, but their individual sizes vary greatly. Schizophyllum uranosum, found in Ordovician strata in Portugal, is one of the largest trilobites, with a length of 70 cm. However, tiny trilobites, such as archaeophaga and ladybug, are less than 6 mm, and common trilobites are generally 3 to 10 cm long and 1 3 cm wide. Anything over 20 cm is considered large. Lydri scoliosis with a length of 30cm was found in the Early Cambrian strata in Kunming, China. Trilobite Trilobite lived a long time ago, but scientists have fully understood its shape, structure and other characteristics. The main reasons are as follows: first, trilobites are covered with a solid carapace, and they have experienced many times of shell growth during their individual development, so they leave more fossils in the stratum than other organisms; Secondly, there are few animals bigger and fiercer than trilobites in the Cambrian ocean, so they can multiply rapidly and distribute widely. In addition, trilobite fossils are mostly preserved in fine limestone or shale, so we can clearly observe not only the characteristics of the shell, but also its internal structure sometimes. The main feature of trilobites is the dorsal shell structure, and there is a prominent "head saddle" in the center of the head, which may be the place where the brain is placed. Some of the surface of the head saddle is smooth and unadorned, some are dotted with tumor spots, and some have varying numbers of transverse grooves. These transverse sulcus are called "head saddle sulcus". There are usually a pair of eyes on both sides of the saddle. There is a groove in front of and behind the eyes, which is called "surface line". This is where trilobites use their shells to drill out of their bodies during their growth. There are a pair of segmented tentacles at the front end of the head and abdomen, which are both acting organs and sensory organs. Behind the tentacles is a mouth for eating, usually covered with a "lip". There are many small and segmented moving organs on both sides of the mouth-appendages with fine cilia, which can probably play a role in breathing. The trilobite's chest is divided into several segments, many of which reach more than ten segments, and a few of which are only divided into two segments. The parts are connected in the shape of shingles (that is, one piece covers the other, just like the tiles on the roof), which is easy to curl. There are many segmented appendages on both sides of the ventral surface of trilobites, and the appendages have cilia, so these appendages are also used for negative movements and breathing. The trilobite's tail, like the chest, is longitudinally divided into the central axis and its ribs on both sides, with various shapes; Some have thorns on the edge of the tail, and some have no thorns. Seen from the back, the trilobite eggs are round or oval, and the adults are 3 ~ 10 cm long and 1 ~ 3 cm wide. The small size less than 6 mm can be divided into three parts: the head armor, the breastplate and the tail armor. The trilobite's body is covered with a shell, the hard shell is the back shell, and its belly edge extends to the ventral surface. The abdominal limb is chitin, and other parts are covered by soft membrane. Generally collected trilobite fossils are dorsal shells. The middle part of the trilobite's dorsal shell is called axis or central axis, and the left and right sides are called ribs or ribs. The surface of trilobites' shells is smooth. Or there are pits, tumors, spots, radial lines, concentric lines, short thorns, etc. Most of the head is vertically divided into three leaves by two dorsal sulcus, the middle part is the head saddle and neck ring, the cheeks are on both sides, and the eyes are located on the cheeks. The cheek is crossed by the upper thread, the inner part between the two lines is collectively called the head cover, and the two sides are called the movable cheek or the free cheek. The chest is composed of many different thoracic segments, with 2 ~ 40 adult segments. The middle part is the central axis, and both sides are called ribs. There is a rib groove on each rib node and an intercostal groove between two rib nodes. The tail is composed of several segments, ranging from 1 to more than 30 segments. The shape is generally semi-circular, but it varies greatly and can be divided into a central axis and two ribs. Rib, rib groove and intercostal groove. Ribs can be ribbed, and there are often thorns on the ribs. The abdominal arthropods of trilobites are rarely preserved as fossils. So far, only 19 species of arthropods have been found in the world. From Ordovician to the end of Devonian, some trilobites (such as trilobites) evolved very ingenious spinelike structures. This fossil was found in Morocco. In addition, fossils with spinal structure have also been found in western Russia, Oklahoma, USA and Ontario, Canada. This spinal structure may be a resistance to the appearance of fish. Eyes Most trilobites have eyes, and they may also be used as antennae for taste and smell organs, which can reach 20 to 30 cm. The eyes of trilobites are made of calcite (calcium carbonate, CaCO 3). Crystallized pure calcite (Iceland spar) is transparent. Some trilobites use single crystals and transparent calcite to form the lens of each eye. This is different from most other arthropods, with poor sphericity, excellent visual effect and depth of field. Ophiocoma wendtii, a hydrangea starfish, uses similar lenses in animals living today. Typical trilobite eyes are compound eyes, and each lens is a slender prism arranged in a hexagonal shape. The number of lenses in each compound eye varies, some are only one, and some can reach thousands. Some trilobites are blind. Maybe they live in the deep sea, where there is no light, so they don't need eyes. Some (such as Phacops rana) have big eyes. Body trilobites look strange. The body is divided into three parts: head, chest and abdomen. Shells, on the other hand, have three leaves, two on each side of the longitudinal axis, so they are called "trilobites". Seen from the back, the trilobite eggs are round or ovoid, and the adults are 3 ~10cm long and1~ 3cm wide. The shell is hard, the middle is convex, and the ribs are low and flat, which also forms a row of three parts. That's how the trilobite got its name. Trilobites are easily preserved as fossils because of their hard back shells. We know today that this extinct animal is known through fossils. The head of a trilobite is called a headgear because it is covered with hard armor, and the central bulge on the headgear is called a head saddle. The shape and size of the head saddle vary greatly among different species. The front of the head saddle is the skull, on which there are eye ridges, eye lobes and eyes. The edges of both sides of the skull are depressed and extend to form movable cheeks, which often further form very sharp buccal spines and extend to the back of the body. The whole headdress is an important basis for trilobite classification and species identification. The breastplate at the tail of the breastplate consists of many similar chest segments, which are connected with each other and are similar to the body segments of most arthropods. The thoracic segment can move and has the function of bending. The trilobite's body can curl or stretch completely by these movable thoracic segments, but the young trilobite has no thoracic segments. The coccygeal refers to the terminal part of the trilobite body, which is formed by the fusion of several body segments to form the unique tail of the trilobite. The tail of trilobites is generally semicircular, and the tail spines of different sizes are often formed at the edge of the tail, which makes many trilobites stretch and radiate and become beautiful. The whole trilobite's back is hard and smooth, but scientists have found that some species have small tumors or nodules on the carapace, which together with the cheek thorns, rib thorns and tail thorns on the carapace constitute a complex protective "armor". Life habits trilobites coexist with corals, sea lilies, brachiopods, cephalopods and other animals. Most of them adapt to crawling or semi-swimming in shallow sea bottom, and some of them swim or float in the ocean. Different living habits determine their different body structures. Seabed trilobites have a flat body, and some trilobites can live in mud. Their head structure is hard, and their front edge looks like a flat shovel, which is easy to dig. Some head nails are healed, ribs are developed, tails are small, and there are spikes, which are used to move forward in the sediment. In addition, the species that are suitable for crawling on the soft or muddy seabed have developed ribs and tail spines, and the body is not easy to sink into mud. This plankton is usually covered with slender spines. They feed on the corpses of small organisms such as protozoa, sponges, coelenterates, brachiopods or algae. Trilobites have a variety of living habits, the most common kind of fossils are preserved in limestone or shale, which shows that most of them lived in shallow sea bottom or swam on mud at that time. Some of them can swim, while others go with the flow. In the Middle Silurian, almost all the teeth were surrounded by dense long spines, which were powerful propellers for them to swim in the water, so it can be inferred that they were experts in swimming. At the same time, these long thorns are also effective weapons against natural enemies. This type of trilobite mainly occurs from Ordovician to Devonian. At that time, nautilus, horseshoe crabs and fish coexisting with them were all enemies of trilobites. If trilobites don't enhance their swimming ability and defensive weapons, how can they continue to survive and reproduce in such a competitive environment? Some Ordovician trilobites, such as twins, strabismus, cryptocephalus, etc. , but also developed the ability to curl, their heads and tails can be completely close together, only showing the hard shell on their backs; They can also drill into the mud to protect their soft abdominal organs, on the one hand, it is convenient to defend the enemy; On the other hand, it can also push the body forward in a way similar to an inchworm. Trilobites are hermaphroditic and oviparous. In the process of individual development, they undergo multiple periodic molting, and their morphology changes greatly. It is generally divided into three stages: larval stage, segmented stage and adult stage. For the individual development process of trilobites, scientists usually study it by collecting samples of the same individual at different growth stages at the same level. The individual development of trilobites can be roughly divided into three periods-infancy, middle age and adulthood. Larvae head and tail are not clear, and there are no thoracic segments, with a diameter of about 0.24 ~1.3 mm. The head and tail of middle-aged worms have been separated and the thoracic segments have developed, but the number of segments is less than that of adults. In the adult stage, the number of nodes in the chest and tail of the worm increases to the limit, the worm body increases, and thorns, tumors and other appendages appear on the shell. After years of research by paleontologists from all over the world, it is considered that trilobites have complex development stages. Trilobites are dioecious and oviparous. During their lifetime development, they have to shed their shells many times to grow up. At present, many arthropods have inherited the growth pattern of trilobites. Trilobites generally go through three growth stages from larvae to adults, namely, larval stage, segmented stage and adult stage. Knowing this is necessary for us to collect trilobite fossils in the wild. If people know a little about the development stages of trilobites, they can make a general identification of the collected trilobites, so as to avoid treating the same trilobite at different development stages as a genus with different forms. The larvae hatched from the eggs of trilobite fossils are called protaspid period, during which all the rings are fused to form a single armor. In the late growth stage, a new chest ring will be added in front of the tail every time you molt. Since then, the number of annual rings has stopped increasing during molting, and people have a rich understanding of the trilobite larval stage, which provides very important help for studying the genetic relationship between trilobites. Besides being small, young trilobites often have obvious bulges, no obvious distinction between head and tail, no chest segment and a spherical body. Later, with the continuous growth of trilobites, the thoracic segments gradually increased. When the thoracic segments all grew up and stopped growing, they entered adulthood, which means that trilobites have reached the stage of sexual maturity and can give birth. Every time a trilobite molts its shell, its body will increase, and the number of its thorns, tumors and even the joints of its tail nail will also increase. Trilobites can live carefree in the ocean when they grow up. So far, no trilobite fossils have been found in the terrestrial strata, which shows that this animal really only lives in the ocean. Because trilobite fossils often appear with corals, brachiopods and cephalopods, it shows that they all like to live in warm shallow waters. Trilobites feed on various tiny organisms or are also interested in seaweed and animal carcasses. To be sure, they don't have the ability to attack actively, because trilobites don't have good swimming organs and streamlined bodies, and they travel slowly in the water. From their solid carapace, it can be imagined that once fierce animals (such as nautilus) attack them, trilobites will quickly curl up, protect themselves like pangolins and quietly sink to the bottom of the sea. The ancestors of trilobites may be arthropods, such as Preeg worms or other cryptobiotic trilobites. Early trilobites have many similarities with Burgess shale and other CAMBRIAN arthropod fossils, so trilobites and other arthropods may have a common ancestor before the boundary between Ediacaran and CAMBRIAN. Trilobites first appeared in the small shell fauna in the early CAMBRIAN. Small-shell fauna mainly refers to soft-tongued snails, gastropods, veneer crustaceans and a large number of small (generally only 1 ~ 2mm) and low-grade mollusks, and their taxonomic status is unknown. At that time, the marine conditions were suitable for their survival, and these animals brought rich food sources to trilobites. At that time, trilobites had not encountered strong food in the ocean. Why are there so many trilobites in CAMBRIAN? Through the study of paleoecology, scientists believe that trilobites have a well-adapted lifestyle. Trilobites don't follow a single lifestyle. Some species like swimming, some like floating on the water, some like crawling on the seabed, and some are used to living in mud. They occupied different ecological spaces, and the Cambrian ocean became a trilobite world. In the geological era after CAMBRIAN, this unusual creature coexisted with other invertebrates for a long time before it gradually decreased and declined. China is rich in trilobite fossils. Only in the early CAMBRIAN, more than 200 genera were discovered. Yanzishi Fossil fossils, which are abundant in Taian, Shandong Province, were found to be accumulated by a large number of active trilobites after death. Those "swallows" that appear on the rock surface and want to fly around are actually the tail nails of trilobites with long tail thorns. Evolutionary trilobites developed rapidly and reached the peak of reproduction in the late CAMBRIAN. In order to adapt to different living environments, morphological evolution is varied. Some head, chest and tail are the same size, and their shells are flat and flat, and the head and tail lack obvious decoration. For example, BUMASTUS: some heads are wide and big, and the front edge is surrounded by a flat and wide edge, with neatly arranged tumor particles on them, such as Cryptococcus; In order to avoid injury, some people decorate their chests and tails with long needles, such as litchi. Some shells can also be rolled into a ball, such as CALYMENE. Specifically, since the emergence of trilobites in the early Cambrian, the main structural characteristics of each part have gradually changed in the whole system evolution. These changes mainly include the following aspects: 1, the change of head saddle shape: the head saddle shape of primitive trilobites in the early CAMBRIAN was mostly long cone, and the bulge was not obvious. Later, after the Middle Cambrian, the head saddle gradually became shorter, and the two sides tended to be parallel, becoming cylindrical, and some even became spherical. By the late CAMBRIAN and later trilobites, even the boundary between the head saddle and its cheeks on both sides was unclear. 2. The change of the position of the posterior branch of the epigraph: the end point of the posterior branch of the epigraph of the early trilobite (that is, the posterior epigraph of the eye) often intersects with the posterior margin of the head or the buccal angle; Later, after Ordovician, it often intersects with both sides of the head. 3, eye changes: the eyes of some trilobites. It was crescent-shaped in the early stage, then gradually became smaller and finally disappeared. Another trilobite with more developed compound eyes, the eyes change from small to large, and finally there will be an eye stalk, and the eyes grow on the eye stalk. Many Silurian trilobites belong to this category. 4. Changes of long spines around the body: Trilobites in Cambrian and Ordovician rarely have long spines, while Silurian and later species have more long spines, and the spines are more complicated than before. 5. The trend that the thoracic segment changes from small to small, the tail changes from small to large, and the transverse groove on the head saddle changes from small to small is also manifested in many types of trilobites. The specific reason for the extinction of trilobites is unknown, but the appearance of early fish such as sharks connected by joints in Silurian and Devonian seems to be related to the decrease of trilobites in the same period. Trilobites may provide abundant food for these new animals. In addition, by the late Permian, the number and species of trilobites were quite small, which undoubtedly provided conditions for their extinction in the Permian-Triassic extinction event. Although the previous Ordovician-Silurian extinction event was not as serious as the later Permian-Triassic extinction event, it also greatly reduced the diversity of trilobites. For the individual development process of trilobites, scientists usually study it by collecting samples of the same individual at different growth stages at the same level. The individual development of trilobites can be roughly divided into three periods-infancy, middle age and adulthood. Larvae head and tail are not clear, and there are no thoracic segments, and the diameter is about 0.24-1.3 mm. The head and tail of middle-aged worms have been separated and the thoracic segments have developed, but the number of segments is less than that of adults. In the adult stage, the number of nodes in the chest and tail of the worm increases to the limit, the worm body increases, and thorns, tumors and other appendages appear on the shell. The representative trilobites in each period (540-490 million years ago) represent the Cambrian. Most trilobites have a flat body. The butterfly is considered to be the ancestor of trilobites. In the research, there is a view that Agnostus belongs to crustaceans. The representative trilobites of Ordovician (490-440 million years ago) have various forms, some with snail-like eyes, some with several horns, and some with swimming trilobites, which have a wide field of vision. Because there were few natural enemies in the ocean at this time, the Ordovician became the "trilobite flourishing age". Silurian trilobites (440-420 million years ago) escaped the extinct species of Ordovician, and they multiplied near coral reefs. The representative trilobites of Devonian (420-360 million years ago) have undergone great changes in the marine environment with the appearance of jawed fish. Many trilobites have evolved various decorative parts on their bodies, and researchers believe that these decorations can enhance the defense function and sensory function of trilobites. The representative trilobites of Carboniferous/Permian (360-250 million years ago) flourished after Cambrian. But the extinction in the late Devonian made all trilobites extinct except protozoa. An order of aphids that escaped disaster, having a streamlined body but no thorns or ornaments. Fossil remains in the ancient ocean. The living environment of trilobites is wide from shallow sea to deep sea. Occasionally, the footprints left by trilobites crawling on the seabed have also been fossilized. Today, trilobite fossils have been found on almost all continents, and they seem to exist in all ancient oceans. Trilobite fossils Today, there are tens of thousands of trilobite fossils found all over the world. Trilobites are very suitable as standard fossils because of their rapid development. Very rare trilobite fossils with soft body parts such as feet, gills and tentacles have been found in British Columbia, new york, China and German. Trilobite fossils in China are one of the important fossils in Early Paleozoic, which is an important basis for the division and correlation of Cambrian strata. The main species of trilobite fossils are: Drepanura, Szechuanella, Parasxechuanella, Ctenopharyngodon (Xiangxi), Coronocephalus and Ductina. As early as 300 years ago, there lived a man named Zhang Huadong in Dawenkou, Tai 'an, Shandong. In the 1920s, Chinese paleontologists conducted scientific research on "Batstone" and finally found out that it was a trilobite tail. This trilobite lived in the late CAMBRIAN 500 million years ago and is an arthropod in the ocean. To commemorate the first name given to trilobites in the world, scientists in China translated the Chinese name of this trilobite from Latin to Batworm. The earliest trilobite record abroad can be traced back to 1698. At that time, Luther named a trilobite fossil with three round tumors on its head as "three tumor worms". By the year of 177 1 year, according to the morphological characteristics of this animal, walch's body can be divided into three parts in both vertical and horizontal directions: the head, chest and tail in vertical direction, the central axis in horizontal direction and its lateral leaves, thus giving a proper name-"trilobite". The earliest trilobite fossil described in domestic research was in Britain, which was mistaken for flounder fossil at that time. 19th century, the research on trilobites abroad has been very in-depth. The trilobites in China were originally named and reported by many foreign experts and explorers. During the Republic of China, Professor Lu initiated an important precedent in the field of trilobite research in China. After the founding of the People's Republic of China, the state began to systematically study trilobites in China. China's trilobites and other books have been published. Professor Zan, curator of Jilin University Museum, made a systematic study on CAMBRIAN trilobite fauna in Liaodong (Liaodong Peninsula and Taizihe Valley). Trilobite fossils in Cambrian strata in this area are described as 4 1 family or subfamily,1genus or subgenus, 189 species, including 5 new genera and 57 new species. Published a series of research results such as the monograph Cambrian Strata and Trilobite Fauna in Liaodong. Trilobite fossils found in the world today can be divided into tens of thousands of species. Because of the rapid development of trilobites, they are very suitable as standard fossils, and geologists can use them to date rocks containing trilobites. Trilobite is the earliest and widely attractive fossil, and new species have been discovered every year. However, due to the late start of trilobite classification in China, the research on trilobite classification in China is still very confusing. Biological significance after the emergence of trilobites, they can be regarded as the representatives of many organisms in the whole Early Paleozoic (including Cambrian, Ordovician and Silurian). Together with many other creatures, they opened the curtain for the earth to enter biodiversity, and since then, a thriving biological world has really appeared. In the late Paleozoic, with the appearance of a large number of marine invertebrates, the number of trilobites decreased and finally became extinct when Mesozoic came. Song Lishan Trilobite1958 April 15 China issued a set of stamps on "Paleontology of China". The first set of stamps were "Song Lishan Trilobite, Lufenglong, and swollen bone deer" from left to right. Recently, AlanDrummond, a scientist at the University of Chicago in the United States, used this method to reproduce an extinct ancient prehistoric species: trilobites, other trilobites or China. News Strange Paleontological Fossils Found in Youyang, Chongqing (1/8) [4] On September 18, the author found some strange insect fossils in Maoba Village, Maoba Township, Youyang Tujia and Miao Autonomous County, Chongqing, and several local villagers saw these fossils at the scene. Chen/Dongfang IC is about 7 cm long and 3 cm wide, and the outline of unknown paleontology is clearly visible. The biggest feature of these fossils is that the feathered tentacles are lifelike. According to some old people, this is called trilobite fossil, which is estimated to be hundreds of millions of years ago. Fossils were found on such rocks. The lines left by insects are clearly visible. Strange fossils found by local villagers. Paleontological fossils are non-renewable geological natural heritage left over from the general geological history of earth evolution, which has important reference value for the study of geology, geology and climate. Youyang, located in the hinterland of Wuling Mountain, is rich in paleontological fossil resources. At present, the author informed the local * * * of this situation, and the other party said that it would send someone to conduct a field trip. Trilobites are the most representative ancient animals, which appeared in CAMBRIAN 560 million years ago. It reached its peak 500-430 million years ago and was completely extinct in Permian 240 million years ago. It has lived on the earth for more than 320 million years and is an extremely vital creature. In the long course of time, they have evolved into many species, some as long as 70 cm, some as short as 2 mm, and their carapace is divided into two dorsal grooves, one axial leaf and two ribbed leaves, hence the name trilobite. (data map)