Several million years ago, our land was inhabited by strange and unexplored animals. According to the theory of evolution, all living organisms originated from each other. One species evolved into another, and so on. Today, all animals on the planet are the result of improvement. For example, ichthyosaurs, stegocephalians and trilobites. The latter are the ancestors of modern isopods. And the ancestors of trilobites are spriggins, organisms living in the Proterozoic era. The size of the creatures reached up to 3 cm.
Who are trilobites?
Trilobites are the first class of arthropods that lived on the planet in the deep bowels of the ocean. Their population disappeared 200 million years ago. But scientists and archaeologists are still finding trilobite fossils.
The heyday of the "kingdom" of trilobites falls on the Paleozoic era. At the end of the era, the number of these amazing creatures exceeded the number of all multicellular animals that lived at that time. If it was the era of dinosaurs, then the Paleozoic - trilobites. This is a scientific assumption.
Appearance description
The structural features of the body of trilobites are based on the hypotheses put forward and the research of scientists. Findings of the remains help to restore the picture of the appearance of arthropods.
shell
The body of a prehistoric creature had a flattened shape. In addition, it was completely covered with a hard shell, consisting of several parts. The size of these creatures ranged from 5 mm to 81 cm. Trilobites could have spikes or horns on the hard surface.
There were other subspecies that could curl up and hide their body in a shell. The pharynx of this animal was located on the peritoneum. The thick "armor" for these arthropods also serves to attach internal organs. In small trilobites, the coating was impregnated with chitin, in large individuals, with calcium carbonate. This is necessary for excellent strength.
Internal organs and reflexes of the body
The head was round. It contained all the most important organs for life: the brain, heart and stomach. In this regard, the head was also covered with a hard shell. In addition, the limbs of trilobites are functions of the motor, chewing and respiratory systems. Undoubtedly, they are no less significant reflexes in the body of prehistoric creatures.
But the most remarkable of the extinct trilobites were the sense organs. True, in some individuals they were absent. lived in muddy water or at the very bottom of the ocean. In other subspecies, the sense organs were located on strong legs. When they burrowed into the sand, their eyes remained on the surface.
But what is especially surprising is the faceted structure of the eyes. Trilobites, instead of the usual lens, had lenses made of mineral calcite. Arthropods had a 360 degree visual angle.
These creatures had small antennae located on their heads. Trilobites lived mostly on the seabed. But there were such specimens that lived in algae and in the water column.
Trilobite evolution
For the first time, these extinct animals appeared in the Cambrian period. But already in the Carboniferous era, their population began to slowly decline. When the end of the Paleozoic period came, the extinction of trilobites became inevitable.
In the process of their development, they acquired a tail and a head section. It was not divided into separate sections, but had a solid shell. The tail section has also changed: it has increased significantly in size. This was very helpful, because when cephalopods appeared, they began to eat arthropods.
Nutrition and reproduction of trilobites
There was more than one species of these amazing organisms. Some ate algae and silt, others - plankton. But there were predatory individuals on the planet. Despite the lack of jaws, they crushed their prey with the help of tentacles. The evidence for this hypothesis was the finds of food in the stomachs of trilobites. These were the remains of brachiopods, sponges and worm-like creatures. It was assumed that carnivorous trilobites attacked their victims, who lived in the ground. Also, extinct organisms could eat ammonites. This was evidenced by the found fossils.
Examining the remains, scientists came to the conclusion that the extinct animals were of different sexes. Confirmation of this was the discovered hatching bag. The female laid eggs. After some time, a larva (1 mm) hatched from there and slowly moved along the bottom.
At first she had a solid body. Then gradually increased the mass and was divided into 6 segments. Trilobites, like all arthropods, periodically molted. Due to this, the larva rapidly increased in size by attaching another segment. Having reached the peak of its growth, the body does not stop shedding.
Trilobites in the modern world and their extraction
The only animals that are remotely similar to trilobites are horseshoe crabs. They also appeared in the Ordovician era. Five species of these creatures live in the oceans to this day. Horseshoe crabs are similar to trilobites in several ways: mode of movement, dorsal carapace, and Both species are antics of the same ancestor, but horseshoe crabs still belong to a different class of arthropods.
Surprisingly, the remains of trilobites are still found. And not in the depths of the seas or oceans, but in ordinary habitable places in Russia. Most of all they met in the Leningrad region and in eastern Siberia (Yakutia). In Yakutia, trilobites are diverse and abundant. But all their hard coatings are either crushed or divided into segments. In the Leningrad region, the opposite is true: the number of extinct creatures is much smaller, but the fossilized remains are striking in their safety. In these places, trilobites are found with a solid shell and a dark brown color. This is due to incompletely decomposed organic matter.
Due to their aesthetic appearance, prehistoric animals in the Leningrad region are considered the main exhibits for sale abroad. Foreign collectors have a very great interest in these amazing creatures. This is good, but regular excavation work leads to the destruction of the surrounding area. As a result, the flora and fauna of those places suffer. And sometimes the structure of trilobites suffers from the barbaric attitude of the collectors. They could easily collect arthropods from other animal parts.
From all over the country they write that they allegedly find living trilobites. However, these are just shields that belong to crustaceans. Simply put, crustaceans that do not crawl, but swim. The size of these creatures reaches up to 8 mm in width. Indeed, they are very similar to trilobites. But here convergence is to blame (animals in the process of evolution acquire a similar image to each other).
Trilobites are typical Paleozoic invertebrates. They appeared over 580 million years ago, quickly flourished, and at the end of the era they died out and completely died out. These bottom marine animals remotely resembled wood lice or bugs. Trilobites can be called relatives of both the first and second, since they are considered the ancestral group for many arthropods.
Despite the significant species diversity - and there are about 4000 species of these arthropods - all trilobites have approximately the same structure of their chitinous shell, similar in strength to the shell of crayfish. By the way, it was the structure and appearance of aquatic animals that determined the decision of scientists when choosing a name for them.
Stone "beetles" in the past were actively mined by enterprising people, from whom they were bought up by no less enterprising merchants in order to resell them at a very high price. The prints of the "beetles" were recognized as magical, protecting against illness and adversity. The trilobite trade flourished.
Translated into Russian, the word "trilobite" means three-lobed, since the body of the bizarre "bug" was divided into three longitudinal rows of plates-blades. The central row, or rachis, served as the axis of the body. On both sides, lateral lobes, the pleura, were attached to the rachis. This is what the torso looked like. The head section was formed from a large lobe-akron, which formed a real shield.
The caudal region often consisted of a single anal lobe - the telson. Sometimes adjacent pleurae were attached to the telson, forming with it a pleated "skirt" - the pygidium. The oral cavity, which included the rigid postoral segments of the carapace, was located on the ventral side, that is, under the acron shield. The eyes were located, on the contrary, from above. Trilobites crawled on the silt or swam low above the bottom, turning over with their tiny legs.
Arthropods are small. The largest individuals that lived on the planet 580-550 million years ago reached a length of 75 cm. The rest of the "bugs" did not exceed the length of the palm, representatives of many species grew only up to 1-2 cm.
Different types of trilobites sometimes differed greatly from each other in size, body shape, and so on. The differences even extended to the shape of the eyes. Some of the trilobites were blind, while others had eyes in a continuous belt along the edge of the acron. The division of the body into three rows of plates was the same for all species.
Such dwarfs, for example, were one of the last trilobites on the planet, who lived in the period from 300 to 290 million years ago in the waters of warm seas that invaded the territory of the Moscow Region and left limestone strata in the place of Myachkovo, the Gzhel River and in other places. These creatures were named Phillips in honor of the English geologist J. Phillips, who singled out the Cenozoic era in the history of the Earth. Naturally, trilobites could not be formidable predators; they were content with small invertebrates and organic remains, which were found in bottom sediments.
Then, when the number of segments is sufficient, the larva stops dividing, but only grows and molts. Paleontologists know a lot about the biology of trilobites. These arthropods serve as Paleozoic guide fossils, which means that rocks can be dated with high accuracy without complex physical analyses. And yet, scientists do not know how trilobites appeared, why they acquired shells and for what reason they died out.
Evolution rarely makes leaps, but trilobites - this vast group of animals - appeared as if suddenly, suddenly and ready-made. In the Vendian, we do not find direct ancestors of these arthropods, only distant relatives. Of course, such incidents can always be explained by the incompleteness of the paleontological record: far from all living beings left at least something behind. However, this explanation does not apply in this case.
Individual development in trilobites proceeded through the larval stage. Scientists managed to find the prints of the larva and establish that it increased body segments by dividing.
It is not clear why trilobites, unlike their Vendian ancestors, acquired a hard shell. Along with trilobites, all other invertebrates also acquired calcified protection. The Paleozoic became the time of skeletal life. The traditional explanation of the causes of the "skeletal revolution" is unsatisfactory. This is just a hypothesis, which largely does not agree with the facts. According to her, the Vendian creatures simply did not have enough energy to build hard houses and armor from calcite.
The atmosphere at that time contained little oxygen, so breathing weakly supported the body's metabolism. But 580 million years ago, the amount of oxygen in the atmosphere as a result of photosynthesis carried out by algae increased to 10%. This is the so-called Berkner-Marshall point. It means that now the volume of oxygen will only increase, and the biosphere will never be able to use up the life-giving gas.
The main enemy of trilobites and other inhabitants of the first Paleozoic seas was the shell scorpion. This creature, despite its name, is much closer to scorpions than to crayfish. All crustacean scorpions were predators, grabbing small and large prey with their claws (in different species of different shapes).
Oxidative reactions in nature began to flow violently, prompting animals to benefit from an accelerated metabolism. Invertebrates began to actively bind calcium and build shells, shields, spines, shells, and so on. After 50 million years, one of the bottom worm-like creatures will guess to deposit calcium inside their body, and this is how real vertebrates will appear. Certainly other environmental factors also acted on the trilobites, but we know almost nothing about them.
Little is known to paleontologists about the reasons for the extinction of this group. It is likely that the amazing arthropods have simply exhausted their genetic potential. When nature went through all the possible forms of trilobites, their evolution was completed. A popular version is about the impact of climate change on trilobites. At the end of the Paleozoic, the climate was very severe.
Along with trilobites, arthropods similar to them lived in the seas of the Paleozoic, for example, leanchoils and sanctacaris. The first were armored bottom dwellers. They filtered the sludge, extracting organic particles. Sanctakaris had an elongated body and large legs adapted for capturing prey. These predators attacked small trilobites and leanchoils.
In the polar regions there were small glaciers, and in the tropical zone there were vast deserts. Many seas became shallow, and the water in them became bitter-salty. Some seas were completely cut off from the retreating ocean, turning into large salt lakes. Trilobites are extremely demanding on water quality. It should be moderately warm and have normal salinity. In addition, invertebrates settled only in shallow seas, well lit by the sun.
Severe climatic conditions forced trilobites to retreat to deep-sea areas, where the death of animals was massive. Few have survived since then. Basically, these are invertebrates that have managed to adapt to great depths - lingulas, horseshoe crabs and other creatures. At first glance, the hypothesis seems convincing, but it does not answer the question of why many other organisms died out along with trilobites at the end of the Paleozoic.
When trilobite prints were first found in the Middle Ages, people thought they were beetles. The popularity of these fossils was great, they even got on the coat of arms of the English city of Dudley.
About 248 million years ago, at the end of the Paleozoic era, more than 50% of all plant and animal families died out. Many species of stegocephals, corals, brachiopods, ferns, lepidodendrons and other creatures have disappeared from the face of the Earth forever. This biospheric catastrophe is three times larger than the Great Dying at the end of the Mesozoic, when dinosaurs and other gigantic reptiles that dominated the planet died. Therefore, it is necessary to look for, in addition to those already known to scientists, other, more powerful factors for the death of trilobites that acted on a global scale.
TRILOBITES - FOSSIL ARthropods
Leontyeva T.V., Kudelina I.V., Fatyunina M.V.
OSU, Orenburg
Phylum Arthropoda - Arthropods, Class Trilobita - Trilobites are animals that lived in the Paleozoic seas. They became completely extinct over 200 million years ago. The time of their appearance, flourishing and death was the entire Paleozoic era. Therefore, the Paleozoic era is called the era of trilobites.
Nowadays, Arthropods are the most common type of animal. The number of known species is close to three million. There are far more of them than all other multicellular animals combined. Crayfish, crabs, scorpions, ticks, spiders, centipedes, insects - all belong to arthropods.
Trilobites have survived on Earth only in the form of fossilized remains. To understand what their way of life was, which helped trilobites to exist on Earth for almost 300 million years, scientists are helped by observations of the current arthropods, which are now common almost everywhere. Arthropods can eat such indigestible substances as cellulose, wax, they can consume oil hydrocarbons and methane. They are surprisingly well adapted to life. That is why they have inhabited the Earth for 500 million years. Trilobites were the most ancient of the Arthropods.
Class Trilobita, genus Asaphus expansus (Asaphus expansus) - opdovic
The body of the Trilobites was covered with a carbonate shell, tough and very resistant to chemical attack. The shell not only protected the animal from the outside, but also served to attach the internal organs, primarily the developed motor muscles. The shell was the outer skeleton. The shells of trilobites are quite well preserved in the fossil state, it can be divided, longitudinally and transversely, into three parts (because of this they got their name). When divided in the longitudinal direction, this is the head shield - the cephalon, the body - the thorax and the tail shield - the pygidium; in the transverse - axial and two lateral parts (pleura). The ventral side of the animal, on which the limbs were located - the organs of movement, nutrition, respiration and touch, was unprotected. Therefore, in case of danger, trilobites could fold due to the presence of pander organs. These are diagonal ridges or tubercles with slit-like holes. Trilobites are dioecious animals. Trilobites did not immediately acquire the ability to fold. In the Cambrian period, when they had just appeared and multiplied, only a few species had the ability to fold, and already in the Ordovician, there were almost no species that would not fold.
The eyes of trilobites could see immediately 360 degrees around, in some species they were raised on long stalks. The stalks were hard outgrowths of the shell and could be in danger of being broken.
The shell of trilobites changed several times during their life, it burst (usually in front and on the back) and the animal threw it off. In a short period of molting, when the new shell had not yet hardened, the size of the animal increased rapidly.
A diagram explaining the process of molting in trilobites. Movable cheeks come off along the facial seam, and the animal crawls out of the old shell
In the same place, dozens of trilobite species with shells of various shapes could live. This means that their diet and lifestyle varied greatly.
For a long time it was believed that trilobites (except for planktonic species) could feed only by swallowing the top layer of soil rich in organic matter, since they had soft, seemingly unadapted limbs to capture the prey. New evidence has recently emerged showing that certain species of trilobites were undeniably predators. This is evidenced by a find in Sweden. There were found traces of some animals living in the ground and traces left by trilobites. At the same time, the trace of a trilobite covers the trace of an animal that lived in the ground, and it breaks off. Consequently, trilobites of this species sought out and ate animals that lived in the soil. In Yakutia, trilobites with preserved intestinal contents have been found. It contained particles of the bodies of benthic animals - sponges and brachiopods.
The remains of trilobites are found in many places in Russia, where Paleozoic and especially ancient Paleozoic marine deposits come to the day surface. The most famous of them are in the Leningrad region and in Eastern Siberia (in Yakutia). Yakut trilobites are very numerous and diverse. But their shells are almost always crushed and divided into scutes and segments. In the Leningrad region, the fossilized remains of trilobites are found in smaller quantities. But among them there are many that amaze with excellent preservation. Many shells have retained their original shape and are usually a beautiful chestnut brown. It is given to them by the remains of incompletely decomposed organic matter.
Features of the search and extraction of trilobite remains depend on the type of location. Soft clayey limestones of the Leningrad region are more easily destroyed in the open air than the shells of trilobites. Therefore, as soon as the layer is exposed, the trilobites begin to "peep" out of the rock, as it were. But here fossil remains are rare and at a great distance from one another. In Yakutia, hard, sharp limestones are almost indistinguishable in color and mechanical properties from the trilobite remains contained in them, and visual inspection of outcrops usually does not reveal anything here. But when fossils are discovered, there are usually many of them, and they are evenly distributed in the rock.
Trilobites of the Leningrad region, due to their aesthetic qualities and relative ease of extraction, have now become one of the main objects of export of paleontological remains from Russia. The interest of collectors in them is very great, this is, of course, good, but it is also associated with many troubles. Intensively exploited outcrops quickly become impoverished, and even die completely. Collectors usually have a barbaric attitude towards unique fossils, since they are only interested in the completeness of the shell being mined. At the same time, science irretrievably loses the opportunity to obtain very important information about the sequence of occurrence of species in layers and about the associated fauna.
The class Trilobites is divided into two subclasses, Subclass Miomera and Subclass Polymera.
Miomera (small-segmented) - small (up to 20 mm) trilobites with 2 or 3 body segments. Cephalon and pygidium are similar in size and shape. Distribution - Cambrian - Ordovician. Myomeres have about 100 genera. A characteristic representative is the detachment Agnostida (agnostids). These are myomeres with 2 trunk segments; eyes and facial sutures are absent. A typical representative is the genus Agnostus (Late Cambrian) , which includes small trilobites with head and tail shields of equal size and with two body segments; the tail shield has two small spines behind.
Polymera (polymers or multi-membered). The sizes are different. Carapace with 5 or more body segments. Their representatives had a long geological history and existed from the Early Cambrian to the Permian inclusive. Their heyday occurred at the end of the Cambrian - Ordovician, after which a noticeable extinction was observed. The Devonian was a period of almost complete disappearance of the polymer, with the exception of some genera that existed during the Carboniferous and Permian. The polymers cover about 1500 genera. The subclass is divided into 7 units. Characteristic representatives: the genus Paradoxides (Middle Cambrian), Asaphus (Middle Ordovician), Phillipsia (Carboniferous-Permian).
Diagram of the geochronological distribution of Trilobita
Trilobites are an extinct group of arthropods, so we cannot present the features of their life with sufficient reliability. Trilobite remains are found only in marine sediments. Most trilobites were inhabitants of the shallow sea, crawling along the bottom or swimming slowly near the bottom - they were benthic animals (they have a flattened body shape, an unprotected ventral side). Trilobite larvae were part of the plankton and widely settled in the ancient seas. The remains of trilobites are found in the form of parts of the shell, usually these are head and tail shields. Trilobite shells are usually found in fine-grained terrigenous rocks - sandstones, siltstones, mudstones, clay shales, as well as in various limestones. Together with trilobites, there are brachiopods, bivalves, bryozoans, corals and other invertebrates.
The abundance, diversity and rapid variability of trilobites make it possible to use them for age determination. With an abundance of shell remains, trilobites can be rock-forming. Starting from the Silurian, the number of trilobites decreases and by the end of the Paleozoic they finally die out.
In modern fauna there is a group of arthropods that are similar in appearance to later trilobites. These are isopods, or isopods. When looking at the shell from above, some of them are difficult to distinguish from trilobites, they give out only thick, consisting of large antenna segments. Isopods, like trilobites, have the ability to curl up and have large compound eyes. For example, common woodlice (terrestrial isopods), when disturbed, curl up into a dense, pea-like ball that can roll, bounce when hitting hard objects, etc. The similarity of isopods and trilobites is due not so much to kinship (in general, rather distant - they belong to different classes such as arthropods), but to a similar principle of body construction, and therefore, the same way of life. It may very well be that in the ecology of the sea, isopods have occupied the vacated niche of extinct trilobites.
Trilobites are the oldest arthropods, so their study is important for understanding the evolution of the type. Trilobite remains are most often internal cores or impressions, with or without a shell. The carapace is rarely preserved intact; it disintegrates along the lines of the movable articulation. The remains of shields are found on the surface of the bedding of rocks. During preparation, it is necessary to preserve the outer surface of the shell, which is then examined under a microscope. Rolled trilobites are successively ground down. The first descriptions and images of trilobites have been known since the end of the 18th century. The first scientific research belongs to K. Linnaeus (1745). A great contribution to the study of trilobites was made by domestic scientists E. Eichwald, F. Schmidt, N.E. Chernyshova, Z.A. Maksimova, N.V. Pokrovskaya and others.
Bibliography
Trilobites - the inhabitants of the Paleozoic [Electronic resource]: Science and life. magazine - Electron. magazine - M: 2002. - Access mode: http://www.nkj.ru/ -№2. 2002.
Leontieva, T.V. Fossil arthropods: guidelines for laboratory studies / T.V. Leontiev; G.S. Malkin. - Orenburg: GOU OSU, 2006.-18s.
Trilobites
Trilobites are marine arthropods that are no longer on Earth. They became completely extinct over 200 million years ago. The time of their appearance, flourishing and death was the entire Paleozoic era.
And it began 550 million years ago and lasted about 300 million years.
At times (especially in the early Paleozoic) there were so many trilobites that in terms of abundance and diversity of species they surpassed most groups of multicellular animals that lived then.
Therefore, if the Mesozoic era (approximately 70-230 
million years ago) can be called the era of dinosaurs, then the Paleozoic - the era of trilobites.
Arthropods are the most prosperous, most numerous type of animal in our time. The number of known species is close to three million. There are far more of them than all other multicellular animals combined.
Crayfish, crabs, scorpions, ticks, spiders, centipedes, insects - all belong to arthropods. And the most simply arranged of all these flying, crawling, running creatures were trilobites, about which the story will go.
Trilobites have survived on Earth only in the form of fossilized remains. To understand what their way of life was, which helped trilobites to exist on Earth for almost 300 million years, paleontologists and biologists are helped by observations of the current arthropods, which are now common almost everywhere.
They live on earth and underground, in fresh and salt water, in puddles and at the bottom of the oceans, on snow and in hot springs, they are found in the Arctic and Antarctic, mountains and deserts. Arthropods have mastered, probably, all the ways of feeding that are possible for multicellular animals.
Arthropods can feed on indigestible substances such as cellulose, wax and horn, they can consume oil hydrocarbons and even, possibly, methane.
In a word, they are surprisingly well adapted to life. That is why they have inhabited the Earth for 500 million years. And trilobites were, apparently, one of the most ancient among them.
The body of arthropods is covered with a chitinous shell, tough and very resistant to chemical attack.
The shell not only protects the animal from the outside, but also serves to attach the internal organs, primarily the developed motor muscles.
For small and medium-sized arthropods (from fractions of a millimeter to several centimeters in length), the strength of a purely chitinous shell is quite enough.
In larger ones (and trilobites, some species of which reached 80 centimeters in length, can be considered large arthropods), the shell is also saturated with mineral salts, mainly calcium carbonate, which gives it special strength.
It is thanks to this lime impregnation that the trilobite shells, having lain in the ground for hundreds of millions of years, are well preserved.
The shell of trilobites can conditionally be divided, both in the longitudinal and transverse directions, into three parts (because of this they got their name).
When divided in the longitudinal direction, these are the head shield, trunk and tail shield; in the transverse - axial and two lateral parts.
Only the dorsal side of the shell was impregnated with lime, while the abdominal side, on which the limbs were located - the organs of movement, nutrition, respiration and touch, on the contrary, was very soft and tender. In case of danger, to protect the soft abdomen, trilobites could curl up.
Interestingly, they did not learn this right away. In the Cambrian period (the first period of the Paleozoic era), when they had just appeared and multiplied, only a few species had the ability to fold, and already in the next geological period - in the Ordovician - there were almost no non-folding species.
It is possible that before there was no need for such an ability, since there were still very few cephalopods (they became the main enemies of large marine arthropods) ....
Candidate of Geological and Mineralogical Sciences A. IVANTSOV, Senior Researcher, Paleontological Institute of the Republic of Armenia
Trilobites- it's extinct Class the first arthropods that appeared on the planet. They lived in the ancient oceans more than 250,000,000 years ago. Paleontologists find their fossils everywhere.
Some even retained their lifetime coloring. In almost any museum you can find these amazing exhibits, some collect them at home. That's why trilobites can be seen on numerous photo.
They got their name because of the structure of the body. Their shell was divided into three parts. Moreover, it could be both longitudinally and transversely. These prehistoric ones were widespread, and very diverse.
To date, there are about 10,000 species. Therefore, it is deservedly considered that the Paleozoic era is the era of trilobites. They died out 230 ml years ago, according to one hypothesis: they were completely eaten by other ancient animals.
Features and habitat of trilobites
Description appearance trilobite based on many findings and research conducted by scientists. The body of the prehistoric animal was flattened. And covered with a hard shell, consisting of many segments.
The sizes of these creatures ranged from 5 mm (conocorypha) to 81 cm (isotelus). Horns or long spikes could be located on the shield. Some of the species could fold their soft body, closing with a shell. The mouth opening was located on the peritoneum.
The shell also served to attach the internal organs. In the small size of trilobites, it was simply made of chitin. And for large ones, it was also saturated with carbonate calcium, for greater strength.
The head had a semicircular shape, and covered with a special shield, served as armor for the stomach, heart and brain. These vital organs, according to scientists, were located in it.
limbs trilobites performed several functions: motor, respiratory and chewing. The choice of one of them depended on the location of the tentacles. All of them were very soft and therefore rarely preserved in fossils.
But the most amazing of these were the senses, or rather the eyes. Some species did not have them at all: they lived in muddy water or deep at the bottom. In others, they were on strong legs: when the trilobites buried themselves in the sand, their eyes remained on the surface.
But the main thing is that they had a complex facet structure. Instead of the usual lens, they had lenses made of mineral calcite. The visual surface of the eyes was positioned so that the arthropods had a 360-degree field of view.
In the photo, the eye of a trilobite
The organs of touch in trilobites were long antennae - antennas on the head and near the mouth. The habitat of these arthropods was mainly the seabed, but some species lived and swam in algae. There are suggestions that there were also specimens living in the water column.
Evolution and in what period did trilobites live
First trilobites appeared in the Cambrian period, then the heyday of this class began. But already in the Carboniferous period, they began to gradually die out. And at the end of the Paleozoic era, they completely disappeared from the face of the Earth.
Most likely, these arthropods originally descended from the Vendian primitives. In progress trilobite evolution acquired a tail and head section, not divided into segments, but covered with a single shell.
At the same time, the tail increased, and the ability to curl up appeared. It became necessary when cephalopods appeared and began to eat these arthropods.
In the modern world, the vacant niche of trilobites was occupied by isopods (isopods). Outwardly, they are very similar to the extinct species, differing only in thick antennae consisting of large segments. Appearance trilobites had a great meaning for the development of the animal world and gave impetus to the emergence of more complex organisms.
The entire development of trilobites took place according to the theory of evolution. By the method of natural selection from simpler species of arthropods, more complex ones appeared - “perfect”. The refutation of this hypothesis is only the incredibly complex structure of the trilobite eye.
These extinct animals had the most complex visual system, the human eye is no match for it. Until now, scientists have not been able to unravel this mystery. And even suggest that the visual system in the process of evolution undergoes a degenerative process.
Nutrition and reproduction of trilobites
There were many species of trilobites, and the diet was also varied. Some ate silt, others - plankton. But some were predators, despite the lack of familiar jaws. Food, they crushed with tentacles.
In the photo, the trilobite isotelus
In the latter, the remains of worm-like creatures, sponges and brachiopods were found in the stomach. It is assumed that they hunted and ate creatures living in the ground. could trilobites eat and ammonites. Moreover, in the fossils found, they are often nearby.
Examining the remains, scientists came to the conclusion that trilobites were of different sexes. This is confirmed by the detected hatching bag. A larva, about a millimeter in size, first hatched from a laying egg and began to move passively in the water column.
She had a whole body. After a while, it is divided immediately into 6 segments. And over a certain period of life, multiple molts occurred, after which the size of the body of the trilobite increased by adding a new section. Having reached the full-segment state, the arthropod continued to molt, but already simply increased in size.
