Trilobites are fossil arthropods of the Paleozoic era. Class Trilobita

Several million years ago, our earth was inhabited by strange and unknown animals. According to the theory of evolution, all living organisms descended from each other. One species turned 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 depths 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 occurred in the Paleozoic era. At the end of the era, the number of these amazing creatures exceeded the number of all multicellular animals living at that time. If it was the era of dinosaurs, then the Paleozoic was the era of trilobites. This is a scientific assumption.

Description of appearance

The structural features of the body of trilobites are based on hypotheses and research by scientists. Findings of remains help restore the picture of the appearance of arthropods.

Carapace

The body of the 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. The hard covering of trilobites could have spines or horns.

There were other subspecies that could curl up and hide their body in a shell. The throat 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 essential for excellent strength.

Internal organs and reflexes of the body

The head was round. All the most important organs for life were located in it: 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 thing about extinct trilobites were their 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 sensory organs were located on strong legs. When they buried themselves in the sand, their eyes remained on the surface.

But what is especially surprising is the facet structure of the eyes. Trilobites, instead of the usual lens, had lenses made of calcite mineral origin. The arthropods' visual angle was 360 degrees.

These creatures had small antennae located on their heads. Trilobites lived primarily on the seabed. But there were specimens that lived in algae and in the water column.

Evolution of trilobites

These extinct animals first 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 continuous shell. The tail section has also changed: it has increased significantly in size. This was very useful, 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 also predatory individuals on the planet. Despite the lack of jaws, they crushed their prey with the help of tentacles. Evidence of this hypothesis was the findings 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 feed on ammonites. This was evidenced by the fossils found.

Examining the remains, scientists came to the conclusion that the extinct animals were heterosexual. This was confirmed by the discovered hatchery pouch. The female hatched 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 it gradually increased its mass and was divided into 6 segments. Trilobites, like all arthropods, molt periodically. Thanks to this, the larva quickly increased in size by attaching another segment. Having reached the peak of its growth, the body does not stop molting.

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 shell, and Both species are descendants of the same ancestor, but horseshoe crabs still belong to a different class of arthropods.

Surprisingly, the remains of trilobites are still being found. And not in the depths of the seas or oceans, but in ordinary inhabited places in Russia. Most of all they were found in the Leningrad region and in eastern Siberia (Yakutia). In Yakutia, trilobites are distinguished by their diversity and huge number. But all their hard coverings 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 preservation. 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 encouraging, but regular excavation work leads to the destruction of the surrounding area. As a result, the flora and fauna of those places suffers. And sometimes the structure of trilobites suffers from the barbaric attitude of collectors. They could easily collect arthropods from other parts of animals.

People from all over the country write that they allegedly find living trilobites. However, these are just shieldfish, which are crustaceans. Simply put, crustaceans that do not crawl, but swim. The size of these creatures reaches up to 8 mm in width. Indeed, they look very much like trilobites. But here convergence is to blame (animals in the process of evolution acquire an image similar to each other).

The remaining nine orders belong to the subclass of polysegmented trilobites.
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The first attempts to classify trilobites were made in 1822 by Brongniart and in 1952 by Barrande.

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There is still a lot of controversy and disagreement around the classification of trilobites.
In the classification of trilobites, a huge role is played by the anatomical features of the body structure of adult individuals. However, such a classification does not allow us to accurately classify all currently studied fossil trilobite specimens.

The website provides a classification of trilobites based both on the anatomy of adults and on the classification of fossil trilobite larvae. This classification is generally accepted throughout the world, but there may be many other opinions of people involved in the problem of trilobite classification.

The classification of trilobites based on the study of larvae was first proposed by Raw in 1925.

Anatomy:

Regardless of size and type, all trilobites had similar trilobed (trilobed) body structure, which gave the class its name. The three main parts of a trilobite are called the head (cephalon), the segmented body (thorax) and the tail shield or end (pygidium). However, it is not these three parts that give the trilobite its name. Trilobites (trilobed/trilobed) received this name because they had a trilobed body structure: a long convex central axial lobe (rachis), flanked by the right and left pleural lobes (lobes = sides).
The above two types of trilobite division are shown in the figure:

Carapace fossil trilobites consists of three layers of chitin impregnated with calcium salts. The total thickness of the chitinous layers of the shell usually does not exceed 1 mm. Different species of trilobites have different shells; they can be porous, smooth, or sculptured (growths or spines).
In some species of trilobites, the trilobed structure of the shell may be faintly noticeable (lost/erased) (the rachis is not observed or is weakly expressed), which, according to scientists, may be associated with the burrowing lifestyle of these trilobites (for example, in the genus Bumastus).

Cephalon trilobite, i.e. its head is usually semicircular in shape. The cephalon consists of a glabella and a fixigena, collectively called the cranidium. On the right and left sides of the cranidium there are librigens (librigena), right and left, respectively.
- The glabella is the central (axial) part of the cephalon; it can be of different sizes in different types of trilobites. In contrast to the body and pygidium, in the head part of the trilobite, division into segments is observed only in the glabella, but not always (in most cases, the glabella has grooves on the sides or has a completely smooth shape). The number of glabella grooves varies among different representatives of the trilobite class;
- Behind the glabella there is usually an occipital ring, which in shape often resembles the rings of the rachis;
- Librigens are also called the free or movable "cheeks" of a trilobite;

The facial suture is the junction of the cranidium with the librigens;
- In sighted species of trilobites, eyes are located on the cephalon under the eye covers. Read their detailed description below;
- In some species of trilobites, eye ridges extend from the glabella to the eyes, often turning into eye covers;
- According to research, the muscles of the head limbs were attached to the inside of the glabella of trilobites, and internal organs (stomach, heart and brain) were also located;

Presumably, some species of trilobites (mostly blind forms) had organs of touch in the form of bristles located on the cephalon. The reason for this assumption is the presence of pits in some trilobites, which scientists mistake for traces of attachment of bristles; these pits are larger in size than the pores of the trilobite shell.
The trilobite cephalon may also be called the head shield.
The cephalic buccal spines may be located on the fixigene and librigena.
For a detailed description of the cephalon and cheek spines, see the figure:

Types of face seams: Depending on where the back branch of the face seam intersects the edge of the head shield, there are four types of face seams (highlighted in bold lines in the image below):
1) proparium type (A, B, C);
2) opisthoparian type (D, E, Z, I, K);
3) gonatoparian type (G);
4) metaparium type (L).

Thorax, i.e. The trilobite's body consists of a number of movably articulated segments, allowing the trilobite to bend and take a curled-up appearance in case of danger (like modern woodlice). The thorax individually, as well as the trilobite as a whole, has an axial lobe, on the sides of which are the right and left pleural lobes. The segments that make up the convex axial lobe of the thorax are collectively called the rachis, and the segments of the pleural lobe are called the pleura. The pleura along the edges of the trilobite are folded into the abdominal region, forming a doublure (volvulus).
Different species of trilobites have different numbers of dorsal segments (from 2 to more than 100). Most trilobites have between 8 and 20 dorsal segments as adults. There was even a species (Schmalenseeia fusilis) that had no dorsal segments at all. Each segment of the thorax has a pair of jointed two-branched limbs on the ventral side.
Those parts of the dorsal segment that are usually not visible in trilobites (hidden under other segments) are indicated in different colors in the figure:
- in the axial lobe of the segment there is an articular semi-ring (green), which is located under the superior segment. The semiring is usually hidden under the leading segment; it can only be seen in folded trilobites or after the destruction of the trilobite’s body;
- the front flange (lilac) and the rear flange (yellow) have small processes that fit together like a puzzle, forming a single whole trilobite body (thorax) and providing its flexibility;
For a detailed image of the thorax and separate dorsal segments, see the figure:

Pygidium, i.e. The tail shield is the end (back) of the trilobite. The pygidium performs a protective function: in case of danger, the trilobite curls up, and its back part (pygidium) closes with the front part (cephalon), as a result of which the trilobite takes on a rounded shape (like modern woodlice). Like the thorax, the trilobite pygidium consists of a variable number of segments, each of which has a pair of articulated two-branched limbs in the abdominal part. Unlike the mobile segments of the thorax, the segments of the pygidium are immobile, and the pygidium itself is one inseparable whole. The convex axial lobe of the pygidium is called the rachis (as well as the axial lobe of the thorax); the left and right pleural lobes of the pygidium are located on the sides of the rachis. In all trilobites, the rachis tapers towards the end of the pygidium.
Different species of trilobites have different numbers of segments (from one to 30).
Based on relative size, there are four types of pygidium:
1. Micropygidium (micropygous) - pygidium is smaller than the cephalon;
2. Almost standard pygidium (subisopygous) - the pygidium is almost the same size as the cephalon;
3. Standard pygidium (isopygous) - the size of the pygidium is equal to the size of the cephalon;
4. Macropygidium - pygidium larger than cephalon.
Possible relationships between the pygidium and the cephalon are shown in the figure:

On the ventral side of the trilobite in the head part there is hypostome. The hypostome is a movable shield-shaped plate connected to the rostrum (rostral plate) in the ventral part of the head shield. The hypostome is thought to be part of the mouth (sometimes called the upper lip). The hypostome, like the entire exoskeleton, was chitinous. The hypostome covered the internal organs of the trilobite on the ventral side: brain, stomach, intestines; as well as the mouth of a trilobite. Most hypostome are located at the same level with the glabella (floating hypostome and adjacent hypostome), i.e. The hypostome is located directly below the glabella on the opposite side of the cephalon (head). However, it happens that the hypostome is not located at the same level as the glabella (impending hypostome).
Different species of trilobites have different hypostomes, which can help in classifying the species of trilobite. A detailed study of the hypostome can also show how and what this type of trilobite ate.
In isolated cases, trilobites retain the so-called lower lip - postoral metastoma, having a convex shape.
In addition to the hypostome and metostome, the abdominal part of the trilobite's cephalon (head) contains a rostrum (rostral plates), a pair of antennae, and four pairs of limbs.
The edge of the trilobite's shell bends down and forms a strip of varying width on the ventral side of the cephalon, thorax and pygidium; this strip is called doublure (turn-up).
A detailed description of the abdominal part of the trilobite and the hypostome variety is shown in the figure:

Eyes The trilobite is a very complex mechanism consisting of many lenses. There were blind trilobites, such as Ellipsocephalus hoffi. They, according to scientists, lived at great depths, where light did not reach, and therefore they did not need eyes. However, the vast majority of trilobites had a pair of eyes, which were usually part of a fixed cheek - fixigena - in the head part of the trilobite (cephalon). Trilobites Asaphus kowalewski and Cybele panderi had eyes on stalks, which allowed them, buried in the mud, to see what was happening on the surface.
The eyes of trilobites have been carefully studied by scientists. According to the latter, trilobites had stereoscopic vision and were sensitive to any movement. Each eye had up to 15,000 double lenses. These lenses are in many ways similar to those used in modern optical technology.
There is information in the literature that trilobites could have visual organs (eyes) on the hypostome and possibly in the middle of the glabella, but this is not a proven fact (according to the book "Fundamentals of Paleontology. Volume 8. Arthropods. Trilobites and Crustaceans" 1960, p. .25-26).
There are three types of trilobite eyes:
1. Compounded eyes of the “Holochroal” type (holochroic eyes) - contained from 100 to 15,000 small lenses. Lenticular or prismatic lenses are usually hexagonal and sometimes quadrangular in shape. All lenses were in direct close contact with each other and had a common stratum corneum. There was no sclera (white membrane) between the lenses. Most representatives of the trilobite class have holochroic eyes;
2. Aggregated eyes of the “Schizochroal” type (schizochroic eyes) - contained from 2 to 700 lenses. Biconvex lenses have a round shape. Each lens had an individual cornea and was separated from the other lenses. There were very deep sclera between the lenses;
3. Eyes of the "Abathochroal" type (abatochroic eyes) - a rare type of eye containing up to 70 lenses. Each lens had an individual cornea and was separated from the other lenses. The sclera between the lenses corresponded to the size of the lenses.
For detailed photographs of trilobite eyes, see the figure:

Trilobite limbs
Like modern arthropods, trilobites had jointed limbs, i.e. limbs consisting of joints connected to each other. These limbs were located on the ventral side and were bibranched (they branched at the base). The number of limbs varied among different trilobite species. Each segment of the thorax and pygidium had a pair of two-branched limbs in the abdominal part (as shown in the figure below). The cephalon had five pairs of two-branched limbs in the abdominal part (the first pair were antennae attached to the hypostome; and the next four pairs of postoral limbs). In different genera of trilobites, the antennae differed in the length of their constituent segments. The antennas are attached to the hypostome in small recesses. And the post-oral limbs participated in the process of capturing food and moving it into the mouth. The limbs of different segments of a trilobite are practically indistinguishable from each other. The limbs of trilobites of different genera and species have minor differences.
In trilobites of the genus Olenoides, a pair of thread-like limbs were found located at the end of the pygidium (similar limbs can be observed in modern shieldfish); perhaps the same limbs were present in other genera.
It is very rare to find preserved (fossilized) trilobite limbs, as they were very fragile compared to the trilobite shell.
The most famous trilobites with preserved limbs are pyritized trilobites, which were found in a quarry near the city of Rome, New York State, USA (coordinates: +43° 15" 12.00", -75° 24" 30.00").
All two-branched limbs consisted of three component parts:
- coxopodite - base of limbs;
- exopodite - a limb branch consisting of a thin segmented axis equipped with villi. According to scientists, the exopodite performed respiratory functions;
- endopodite - a limb branch consisting of eight different segments. Endopodites were limbs designed for the movement of trilobites, and cephalon endopodites, according to scientists, had the function of capturing and grinding food.

TRILOBITE GROWTH AND MOLTING
Since the trilobite had an external chitinous skeleton, the growth of the trilobite’s body occurred only during molting (shedding of the old exoskeleton), as in many modern arthropods.
The junction of the fixigen and librigen is called the facial suture. During molting, the old exoskeleton shell ruptured along the facial suture line, after which the fixigene shell sometimes came off completely. Since the facial sutures run close to the eyes, the trilobite's eyes were the first to be released during molting. Further, through the resulting hole, the trilobite left the shell of the old exoskeleton.
Most trilobite fossils are exoskeleton shells shed during trilobite moulting. The molting process explains the reason for the frequent discovery of incomplete trilobite specimens (body with pygidium but no head, or only a single pygidium).
Video example of molting in modern arthropods:
http://rutube.ru/tracks/5559771.html
http://rutube.ru/tracks/4226503.html
For a detailed image of the trilobite molting process, see the figure:

The discarded shell differs from a whole fossil trilobite in a number of features:
- the shed shell has no eyes;
- the discarded shell has a clearly visible gap in the line of the facial suture (between the cranidium and the librigens);
- the shed carapace usually has broken areas (torn off pygidium, torn segments of the thorax, cephalon without cranidium or without librigene).
An example of a shell shed during molting, reflecting all of the above characteristics:

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Folding of a trilobite
In a dangerous situation, the trilobite, for defense purposes, could take the shape of a ball, curling up like modern woodlice. When folded, the flexible back curved and the pygidium was connected to the cephalon. This form of self-defense helped preserve the limbs (joints) and soft abdomen. Fossil trilobites are often found rolled up. This indicates that the found sample is the trilobite itself, and not the shell (exoskeleton) shed during molting.
The trilobite's ability to roll up is a means of passive defense against enemies.
Play a huge role in the folding function Pander's organs. Pander's organs were first discovered in 1855 by Russian academician S.N. Pander, and later A. Folbort in 1857, gave the name to these organs - “Pander's organs” in honor of their discoverer.
These organs are located on the doublure of the buccal margins and on the doublure of each segment of the body. Different species of trilobites have different pander organs. According to research by E.A. Balashova (1955) the tubercles of the pander organs play the role of “locks”, i.e. when the trilobite is curled, these “locks” close and the trilobite does not need to use muscles (keep them in constant tension) to maintain the curled shape. Also according to E.A. Balashova holes in the pander organs play a respiratory function at the time of trilobite coagulation - through them water can continuously penetrate under the trilobite’s shell to the gills, which allowed the trilobite to remain in a coiled state for quite a long time.
Photos of trilobites in a folded state:

There are three types of folding of trilobites (according to PIN RAS) shown in the photo below:
1,2,3,6 - spheroidal type of folding (characteristic of most trilobites);
4 - double folding type;
5 - discoidal type of folding.

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FOOD OF TRILOBITES
According to scientists, different types of trilobites ate differently. Among the trilobites there were predators, scavengers, possibly herbivores and possibly filter feeders (water filtering i.e. planktivores).
Based on the results of the research, scientists suggested that trilobites, having a conterminant type hypostome (adjacent hypostome), were predators. Trilobites, having a natant hypostome (floating hypostome), were omnivores (predators, scavengers, and also possibly fed on algae).
Some trilobites (such as Cryptolithus) had a specific head shape with pore openings, which allowed them to easily filter water through these openings. They were believed to be filter-feeding trilobites (an example of the filtration model is shown in the description of trilobites of the order Harpetida).
The trilobite Asaphus kowalewski, which had eyes on stalks, was a predator, according to scientists. A trilobite of this species buried itself in the soil so that its eyes remained on the surface. In this state, he waited for the victim and attacked when the opportunity arose.
Blind trilobites (such as Ellipsocephalus hoffi) were not able to hunt due to the lack of eyes. Apparently they were scavengers.

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REPRODUCTION OF TRILOBITES
Scientists believe that trilobites were bisexual, like most modern aquatic arthropods, and laid eggs. However, there was only a single case of the discovery of eodiscid trilobite eggs laid in 1994. Scientists now suggest that some species of trilobites laid eggs in the preglabellar lobe of the head (cephalon), where a brood pouch was formed in which the young subsequently developed. This method of reproduction is characteristic of modern horseshoe crabs, which are also representatives of arthropods. However, such a brood pouch has never been discovered in some species of fossil trilobites. According to scientists, their eggs could have been laid under the cephalon, in its lower part, slightly above the hypostome.
The presence of a brood pouch is an example of sexual dimorphism in trilobites (difference between male and female sexes).
A detailed image of the location of the brood pouch is shown in the figure below:

Another example of sexual dimorphism of trilobites is the difference between two forms of the same trilobite species:
1) narrow body shape - male;
2) wide body shape - female.
For the first time, such an assumption of sexual differences in trilobites was proposed by Barrand in 1852. In some representatives of modern arthropods, sexual dimorphism is expressed in a similar way.
Another example of sexual differences is the presence/absence of sculptural formations (terrace lines) and the difference in the structure of the occipital ring.

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ONTOGENESIS OF TRILOBITES (development)
Three stages/periods can be distinguished in the development of a trilobite:
1) egg (the size of trilobite eggs ranges from 0.6 mm to 4 mm);
2) development of the larva;
3) adult
Embryonic development of trilobites, i.e. The development of the embryo inside the egg is unknown.
In turn, the development of the larva can also be divided into three stages/periods:
1) Protaspis: larva about 1 mm in size, no eyes, the body is a scute, which is a single whole (not divided into head and tail sections). Protaspis is divided into two periods: anaprotaspis (the larva consists of a segmented head shield) and metaprotaspis (new segments begin to be added);
2) Meraspis: the single shield (body) of the trilobite is divided into head and tail shields; pleural spines appear; one after another, segments of the trilobite's thorax (torso) appear until they reach the maximum number (characteristic of adult forms of trilobites). New segments of the thorax appear in trilobites as they grow, forming between the last segment of the body and the tail shield.
3) Holaspis: the larva is small in size, but all parts of the body (cephalon, thorax and pygidium) are almost complete; the period of trilobite growth begins; The trilobite gradually becomes an adult. Trilobite growth occurs through molting (the molting process was described above).

The study of trilobite larvae contributed to a more accurate classification of trilobites (from orders to genera). This classification method was first proposed by Raw in 1925.


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INTERNAL ANATOMY OF TRILOBITES (or anatomy of internal organs)

Like other animals, trilobites had soft internal organs, which contributed to the rarity of their discovery in fossilized states. However, such cases have been recorded.
In the head part of the trilobite, between the hypostome and metostome, there was mouth opening, it was the beginning esophagus. Under the glabella is stomach, turning into intestines, which in turn passes under the rachis through the entire body of the trilobite and ends anus in the lower part of the pygidium. It is believed that the larger the glabella of a trilobite, the larger the size of the stomach located underneath it. On the sides of the stomach there were associated with the stomach hepatic processes, which are branched thin wrinkles radiating from the glabella to the outer edge. Sometimes these hepatic processes are called gastric diverticula.
Heart was located above the digestive canal and was a long multi-chamber vessel.
Also in the head part of the trilobite is located brain, which is the center central nervous system body (CNS). The brain received information from the visual organs - the eyes (which we described earlier) and from the tactile organs - the antennae (antennae) of the trilobite. The central nervous system of trilobites itself is the abdominal nervous system because passes through the entire abdominal part of the trilobite from the cephalon to the pygidium. The CNS has never been found in fossilized trilobite specimens. According to scientists, the central nervous system consisted of one or two nerve trunks with segmental ganglia(swellings) corresponding to the segments of the trilobite's body.
Also of great interest to science are Pander's organs which are described above in the section “Folding of a trilobite”, these organs were necessary for the trilobite to remain in a folded state for a long time.

Findings:

1. Southern Australia, Emu Bay & Cape D'Estaing, Kangaroo Island, Emu Bay Shale.
2. Germany, Rhine Massif, Rhine Valley, Hunsr Slate.
3. Germany, Rhine massif, Rhine valley, Eifel, near Gerolstein, Gees.
4. Canada, southern British Columbia, Canadian Rockies, Yoho National Park, Burgess Shale.
5. China, eastern Yunnan, Maotianshan and other localities near Chengjiang.
6. Morocco, Anti-Atlas mountains.
7. Russia, Leningrad region: Volkhov River valley; Putilovsky quarry; Vilpovitsy quarry; Lava River Valley and other places.
8. USA, California, San Bernardino, Marble & Providence Mountains, Latham Shale.
9. USA, New York, Middleport, Caleb's quarry, Rochester Shale.
10. USA, New York, Herkimer County, Trenton Falls, Wolcott-Rust Quarry.
11. USA, Ohio, Sylvania.
12. USA, Oklahoma, Coal County, Near Clarita.
13. USA, Utah, House Range & Drum Mountains, Wheeler Shale.
14. Czech Republic, central Bohemia, Litavka river valley, Jince region.
(only the most famous find sites are indicated)

Habitat:

Trilobites were bottom sea inhabitants (benthic, i.e. living on the bottom). Some species of trilobites (Ellipsocephalus hoffi) were deprived of eyes because lived mainly in silt (according to another version, they lived at great depths) in the absence of light. Other trilobites (Asaphus kowalewski) had eyes on stalks and, according to scientists, hid in the mud so that only the eyes were on the surface. According to scientists, some species of trilobites may have been able to swim and their habitat was floating algae (swimming forms of trilobites are also called pelagic, that is, living in the water column).

1. Story. Trilobites were first described by Llwyd in 1698, when they were given the name Trinuclei. Some species described by Linnaeus in 1745 were called Entomolithes (they were classified as insects). The name Trilobita was proposed by Walch and generally accepted in 1771.

2. Diversity of trilobites. Scientists have discovered about 5,000 genera and about 10,000-20,000 species of trilobites (according to various sources). This exceeds the number of mineral species registered by the IMA (about 4600). And makes the trilobite class one of the most diverse biological classes. In addition, in Morocco, where trilobites are hunted on a massive scale, new species are constantly being discovered.
According to the resource trilobites.info, the class Trilobita includes 10 orders, 17 suborders, 32 superfamilies, 170 families and 3944 genera (species number unknown).

3. Trilobite replacement. For the most part, all discovered remains of trilobite exoskeletons are replaced by calcium carbonate (CaCO 3), but the fact of discovery in the USA is known. Such trilobites have another unique feature: they have well-preserved limbs, gill structure, muscles and antennae.

4. Chitin(translated from ancient Greek - clothing, shell, skin), which made up the exoskeleton of trilobites - a natural compound from the group of polysaccharides, part of the cell wall of bacteria and fungi. Chitin exoskeleton often “impregnated” with many calcium salts (calcium carbonate - CaCO 3 ; calcium phosphate - CaPO 4 ), which gives it greater strength. The exoskeleton performs supporting and protective functions. An example of a chitinous exoskeleton is the shells of crayfish, shrimp, crabs and other modern arthropods.

5. The largest trilobite. The largest trilobite found (Isotelus rex) was discovered in Canada (Mantitobs), its length is 72 cm. This trilobite is now in the Museum of Man and Nature in Winnipeg (Mantitobs). Large trilobites are found very rarely and, as a rule, they are incomplete or damaged.
Famous large trilobites:
Isotelus rex - 72 cm (Canada);
Uralichas hispanicus - 66 cm (Spain);
Terataspis grandis - 60 cm (New York);
Paradoxis (Acadoparadoxides) briareus - 45 cm (Morocco);
Isotelus brachycephalus - 33 cm (Ohio), now in the Royal Ontario Museum.
(in the book “Fundamentals of Paleontology. Volume 8. Arthropods. Trilobites and Crustaceans” (1960), on pages 19-20 it is written about trilobites up to 75 cm in size. An example is Uralichas riberoi - about 75 cm.)

6. Trilobite researchers.
Llwyd is credited with being the first to explore trilobites in 1698. After him, trilobites were studied by Linnaeus in 1745 and Walch in 1771.
The classification of trilobites was first undertaken by Brongniart in 1822 and Barrande in 1952.
Then the study of trilobites was carried out by: Brongniart, Dalman, Green, Pander, Emmrich, Burmeister.
- On the territory of the USSR, trilobites were studied by: Pander, Eichwald, Möller, Holm, F. Schmidt, V.N. Weber, E.V. Lermontova, N.E. Chernysheva, N.P. Suvorova, N.V. Pokrovskaya, O.K. Poletaeva, A.G. Sivova, L.I. Egorova, M.V. Lomovitskaya, N.K. Ivshin, M.N. Koroleva, K.A. Lisogor, E.A. Balashova, A. Perna, Z.A. Maksimova, O.G. Tumanskaya;
- In Czechoslovakia and France, trilobite research was carried out by: Barrande, Beyrich, Corda, Oehlert;
- In England, trilobite research was carried out by: McCoy, Salter, Woodward, Reed, Lake, Row;
- In Germany, trilobite research was carried out by: Kayser, Gurich, R. Richter and E. Richter (Rud Richter & Uyu Kshsreuk);
- In the Scandinavian countries, trilobites were studied by: Angelin, Brogger, Warburg, Stormer, Westergard;
- In North America, trilobite research was carried out by: Hall, Walcott, Matthew, Raymond, Resser, Rasetti;
- In Asia, trilobite research was carried out by: Walcott, Mansuy, Reed, Kobayashi, Sun Y.C. and Lu Yen hao;
- In Australia, Whitehouse studied trilobites.
(according to the book "Fundamentals of Paleontology. Volume 8. Arthropods. Trilobites and Crustaceans" 1960)

7. Trilobite shell color. Typically, fossil trilobites have a uniform, uniform color of shell. However, there have been rare cases of discovery of intravital coloration of the carapace of trilobites. Striped and spotted colors of the trilobites Anomocare, Isotelus, and Proetus are described.
Article about red Devonian trilobites with green eyes from Morocco (with photographs): Klug Christian, Schulz Hartmut, Baets Kenneth (2009) - Red Devonian trilobites with green eyes from Morocco and the silicification of the trilobite exoskeleton (http://app.pan .pl/archive/published/app54/app54-117.pdf)

8. Horseshoe crab larva. In modern horseshoe crabs, also representatives of arthropods, the larva has a shape reminiscent of a trilobite. This fact was the reason for giving it the name “trilobite larva”.

9. Scientific films about trilobites. We were unable to find a full-fledged scientific film only about trilobites, but there are several films in which trilobites received decent attention:
BBC: Walking with Sea Monsters Part 1 of 3 (BBC, 2003);
BBC: "First Life" Part 2 of 2 "Conquest" (BBC, 2010).

10. TrilobiteJam- in the state of Utah (USA) on June 14-17, 2012, the 3rd annual collection of trilobite fossils took place over an area of ​​more than 300 acres (1,214,056.93 sq.m.) in the rocks of the Wheeler Shale and Marjum formations. Information about past and future fundraisers can be found at http://www.trilobitejam.com/

11. Trilobite images. Famous images of trilobites:
- The municipality of Murero, district of Campo de Daroca, province of Zaragoza (Caparoca), autonomous community of Aragon in Spain has a coat of arms depicting a trilobite. Murero is famous throughout the world as the "Sistine Chapel of the trilobites".
- In the center of the coat of arms of the English city of Dudley there is a trilobite;
- The emblem of the Czech Geological Society (Ceská geologická spolecnost) depicts a trilobite: http://www.geologickaspolecnost.cz/

12. Trilobite jewelry. Trilobites are sometimes used to make jewelry; in particular, Elrathia kingii is often used to make pendants, inserted into a frame and hung on a chain.

13. Trilobite robot. The name trilobite is also borne by the modern electronic robot vacuum cleaner "Trilobite", produced by Electrolux, which has partial similarities with fossil trilobites.

14. Trilobite sculpture on wheels. Sculptor Jon Sarriugarte teamed up with sound effects artist Kyrsten Mate Comoglio to create a wheeled trilobite sculpture called "Sarriugarteis (Odontochile) trilobite." The structure itself is a small metal chassis covered with metal sheets, giving the sculpture the appearance of an extinct arthropod creature. The device has a control joystick in the head, headlights and underbody lighting for night trips.

15. Restaurant Trilobite. In the city of Prague (Czech Republic), at Palackeho 715/15, Praha 1, there is a restaurant called "Restaurace Trilobit". Restaurant website: http://www.restauracetrilobit.cz

16. Horror film about Trilobites. In 2003, the low-budget film “Deep Freeze” was shot. According to the plot of the film, oil deposits were discovered in Antarctica, during the extraction of which huge trilobites the size of dogs appeared, which killed all the station workers in turn. Throughout the film, oil production workers fight the creatures, but to no avail. As a result, the last surviving station worker blows up the station along with himself and the trilobites.

17. Trilobite is an anime hero and a toy. One of the heroes of the Japanese anime series "Bakugan" ("Bakugan") - Limulus (Limulus) - this Bakugan is called a trilobite, although it looks more like a horseshoe crab. Quote: "Limulus is a trilobite-like Bakugan with very dangerous spikes on its back. The fearsome tentacles can wrap around Limulus' opponents, rendering them helpless. Lumulus uses the enemy's strength to increase its own." (http://www.bakugan.com.ua/collection_bakugans_core_L.php)
Trilobites also served as the inspiration for the character in the anime "Pokemon" named Kabuto (a mixture of a trilobite and a horseshoe crab). (http://wiki.pokeliga.com/Kabuto). Kabuto was featured in three anime episodes: episode 13 "The Mystery of the Lighthouse", episode 46 "Attack of the Prehistoric Pokémon" and episode 91 "Shell Shock".

18. Trilobites on postage stamps. In many countries, trilobites were depicted on postage stamps:
- in a series of six postage stamps of the GDR “Palaeontology”, issued on 02/06/1973, where a trilobite is depicted on the 70Pf stamp (drawing by G. Voigt);
- in 1958 on a Chinese stamp from the paleontological series of stamps;
- in the “British Antarctic Territory” series, two stamps have images of trilobites;
- one Finnish stamp from the Åland Islands series depicts a trilobite of the genus Asaphus;
and many other brands: http://biostamps.narod.ru/systema/ss_00055.htm

19. Trilobite made of paper. The Australian Geological Survey Organization (AGSO) has developed and posted on the Internet a prefabricated paper model of a trilobite that can be printed and assembled at home using scissors and office glue.
You can download the file from the Houston Gem and Minetal Society website: http://www.hgms.org/Paleo/trilobite-model.html
Or via direct link: http://www.hgms.org/Paleo/TRILOBIT.PDF

20. Trilobit Records. In 2012, a record company called Trilobit Records was created in St. Petersburg.

21. Japanese. The word Trilobite in Japanese sounds like “SaYoMushi” (“sayomushi” or “sayomushi”) and consists of three hieroglyphs: “san” - three, “yo” - leaf, “mushi” - insect. Literally from Japanese this word can be translated into Russian as “three-leaf insect.”

22. Music video dedicated to trilobites. In the 80s of the 20th century, director Rocky Schenck shot a video with the participation of the group "Visiting kids" for the song "Trilobites". The clip is aimed at a children's audience and answers in a simple form the question - "who are trilobites?" The clip also shows several types of fossil trilobites. The clip can be viewed here: http://www.youtube.com/watch?v=AHZ7JBz4aEU

23. Tolkien and trilobites. One genus of fossil trilobites from the family Acastidae (superfamily Acastidea / suborder Phacopina / order Phacopida) was named Tolkienia in honor of John Ronald Reuel Tolkien. The genus was described in 1997 on pages 21-22 of the American Museum of Natural History bulletin "Evolutionary and biogeographic patterns in the Asteropyginae (Trilobita, Devonian)" by Bruce S. Lieberman and Gerald J. Kloc.

Morphology

The morphology of the body of trilobites fully corresponds to the organization of the type of arthropods, however, they have similarities with the type of annelids (in particular, their body consisted of many homonomic segments). The body structure of trilobites bears evidence of adaptation to a benthic lifestyle: a powerful shell, flattenedness, compound eyes on the upper side of the body, the location of the mouth and legs on the ventral side of the body. Among trilobites, some groups fed on mud, others on small invertebrates, and some on plankton. Many trilobites were probably predators, despite the lack of jaws. To grind food, they used modified appendages on the bases of the limbs (gnathobases). There were free-swimming, crawling, and burrowing animals.

The body length of trilobites reached 90 cm. The body consisted of a solid head and a segmented torso. The limbs of trilobites are multifunctional, that is, they performed several functions at once - motor, respiratory and chewing. Some trilobites have visible organs of touch - antennae on the head.

According to one version, the ancestor of trilobites was spriggina, a Late Proterozoic organism about 3 cm long. The popularity of this hypothesis is now less than in the past; it is likely that the similarity between these organisms is purely superficial.

The development of trilobites occurred with metamorphosis. Their fossilized eggs and larvae have been preserved. There is evidence that trilobites molted sequentially, and after each molting their body increased by several segments.

Rusophycus, fossil traces of trilobite crawling

A significant part of the fossil finds of trilobites are on dorsal shells, which the animals shed during molting and therefore lack a movable part of the cheek. Less common in fossilized form are non-calcareous parts of the skeleton: limbs (legs) and tentacles. In addition to fossils, trilobites left numerous traces of life activity, including traces of rest (Rusophycus) and crawling (Cruziana and Diplichnites).

The shell (cover of the dorsal side), the features of which are the main systematic features of trilobites, consists of three sections:

• head shield with two mostly well-developed eyes;
• torso (thorax), consisting of a different number of segments movably connected to each other;
• tail shield (pygidium), which differs from the body in that its constituent segments are motionlessly connected to each other.

In addition, by two longitudinal, almost parallel dorsal grooves, the shell is divided into three lobes: a middle one and two lateral ones. The name “trilobites” (“three-lobed”) comes from this division.

Many trilobites had the ability to roll up their bodies in such a way that the entire lower surface was under the shell.

The head shield usually approaches a semicircle in outline. The middle, more or less prominent lobe of the head shield is called the glabella, the lateral ones are called the cheeks; the posterior corners of the cheeks are often elongated into more or less long buccal points. The head shield rarely consists of one continuous part, but is usually divided using special lines or so-called. seams into several separate parts, along which the head shield often disintegrated after death and during the processes of petrification. These separate parts also include a special plate on the wrapped part of the shield, the so-called hypostome (or upper lip), which probably served as a cover for the abdomen. The body is divided into a middle, or axial, part (rachis) and lateral parts (pleura), while on the caudal shield, as a continuation of the 3 corresponding parts of the body, an axial lobe and lateral lobes are distinguished. The axial parts of the body and tail shield in the fossilized state are open from below, since they were covered during life with thin skin, but the lateral parts have preserved a solid turn, usually distinguished by special lines decorating it. The appendages of the ventral side, discovered recently, consist of: 1) four pairs of limbs above the head shield on the sides of the mouth opening, consisting of 6–7 segments and serving partly as chewing organs. The end members of the posterior pair looked like swimming blades; 2) from paired two-branched limbs, located both under the body and under the caudal segments, consisting of a certain number of segments ending in claws. Above the outer branch there were also special two-branched and spirally coiled appendages, considered as gills. According to Beecher's research, in front of the mouth opening there is another pair of long, thin segmented antennae, which are open so far only in a very few trilobites (Triarthrus).

Sense organs

Trilobites had compound eyes, which were set on stalks in those animals that buried themselves in the mud. Representatives of the order Agnostida are completely devoid of eyes, which is apparently associated with life at great depths or in turbid water. Based on the location and number of prisms, the eyes of trilobites are divided into three groups:

1. holochroic, consisting of a large number (up to 15 thousand) of prismatic lenses tightly pressed together, usually covered with a common transparent shell;
2. schizochroic, with a visual surface consisting of rounded or polygonal lenses (up to 700), each of which is covered with a membrane and separated from the others;
3. abatochroic, found in representatives of the Cambrian suborder Eodiscina, and differing from schizochroic in the smaller number (no more than 70) and size of lenses.

Spreading

The number of trilobites is quite large. Barrand also counted over 1,700 species, of which 252 belong to the Cambrian period, in the Silurian period: 866 to the Lower Silurian, 482 to the Upper Silurian era, 105 to the Devonian and only 15 to the Carboniferous period; Only 1 species transitions into the Permian period.

The job of classifying trilobites has been difficult for paleontologists. It turned out that one cannot proceed from any one sign, but must take into account many signs together. The oldest group Olenidae prevails in the Cambrian period - it is characterized by a large number of segments in the body, the predominance of the size of the head over the caudal shield (in other trilobites they are usually equal in size), small development of the eyes and facial suture, and the ability to fold is still poorly developed in them. In the Lower Silurian the group is especially noticeable Asaphidae. Their number of body segments is constant and equal to 8, well-developed compound eyes, the surface is always smooth; family Phacopidae distributed from the Lower Silurian to the Devonian. They have a constant number of segments - 13 - and their eyes have a peculiar appearance. Groups common in the Upper Silurian system Proetidae, Bronteidae, Calymenidae, which pass into the Devonian system; in the Carboniferous system only members of the Proetidae are found.

Particularly well-preserved remains of trilobites are found in Yunnan Province in China (Maotianshan Shale), in Alberta in Canada (Burgess Shale), in New York State in the USA, and in Rhineland-Palatinate in Germany (Hunsrück Shale).

see also

Literature

• Glossary of morphological terms and scheme for describing trilobites. M.: Nauka, 1982. 60 p.
• Basics of paleontology. M.: Gosgeoltekhizdat, 1960. Arthropods. Trilobites and crustaceans, p. 17-194.

Notes

Links

• Illustrations of Ordovician trilobites from the vicinity of St. Petersburg. Archived
• E. B. Naimark. The appearance of homologous series in centers of diversification (using the example of trilobites of the order Agnostida). Archived from the original on November 28, 2012.
• Trilobite Forgery. Archived from the original on November 28, 2012.
• Western Trilobite Association. *Western Trilobite Association.
• Mark Bourrie’s trilobite collection - another collection of photographs of trilobite fossils. Archived from the original on November 28, 2012.
• A Guide to the Orders of Trilobites. Archived from the original on November 28, 2012.
• . Archived from the original on November 28, 2012.

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See what "Trilobites" are in other dictionaries:

- (Trilobita), a class of extinct moras. arthropods. T. are already known from the deposits of the Early Cambrian seas, reaching their peak in the late. Cambrian Ordovician and became extinct by the end. Paleozoic Dl. from 10 mm to 80 cm. The body is segmented, flattened in the dorso-ventral... ... Biological encyclopedic dictionary

Marine crustacean fossil animals are found primarily in the Silurian formation. They became extinct towards the end of the Devonian period. Dictionary of foreign words included in the Russian language. Pavlenkov F., 1907. trilobites (gr. tri... three... +… … Dictionary of foreign words of the Russian language

TRILOBITES, extinct marine arthropods. Over 10 thousand species; lived in the Cambrian mid-Permian; guiding fossils. The fossils preserve the calcareous chitinous shell that covered the dorsal surface of trilobites (length from 1 to 80 cm,... ... Modern encyclopedia

A class of extinct marine arthropods. They lived in the Cambrian mid-Permian. Over 10,000 species were widespread in shallow waters. Body length from 1 to 80 cm (usually 3 10 cm). Leading fossils... Big Encyclopedic Dictionary

Candidate of Geological and Mineralogical Sciences A. IVANTSOV, Senior Researcher at the Paleontological Institute of the Russian Academy of Sciences

Trilobites are marine arthropods that no longer exist on Earth. They went 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 they exceeded most groups of multicellular animals living then in number and diversity of species. Therefore, if the Mesozoic era (about 70-230 million years ago) can be called the era of dinosaurs, then the Paleozoic era can be called the era of trilobites.

Arthropods in our time are the most prosperous, most numerous type of animals. The number of known species approaches three million. There are many more of them than all other multicellular animals combined. Crayfish, crabs, scorpions, ticks, spiders, centipedes, insects - all belong to arthropods. And the most simply constructed of all these flying, crawling, running creatures were trilobites, about which the story will go.

The body of arthropods is covered with a chitinous shell, hard and very resistant to chemical influences. The shell not only protects the animal from the outside, but also serves to attach internal organs, primarily developed motor muscles. Therefore, it can be considered a kind of exoskeleton of these animals. 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 sufficient. In larger ones (and trilobites, some species of which reached 80 centimeters in length, can be considered large arthropods), the shell is also impregnated with mineral salts, mainly calcium carbonate, which gives it special strength. It is thanks to this lime impregnation that the shells of trilobites, having lain in the ground for hundreds of millions of years, are well preserved.

The shell of trilobites can be conditionally divided both longitudinally and transversely into three parts (which is why they got their name). When divided longitudinally, these are the head shield, body and tail shield; in the transverse - an axial and two lateral parts. Only the dorsal side of the shell was saturated with lime, and the abdominal side, on which the limbs were located - the organs of movement, nutrition, breathing and touch, on the contrary, was very soft and tender. In case of danger, trilobites could curl up to protect their soft abdomen. It’s interesting that they didn’t 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 previously there was no need for such an ability, since cephalopods (they became the main enemies of large marine arthropods) were still very few at that time. In the Ordovician, cephalopods multiplied greatly and sometimes reached gigantic sizes. For example, in the sea, which in the Ordovician period was on the territory of the present Leningrad region, there lived cephalopods with shells five meters long.

Folded shell of the trilobite Pliomera fischeri (front view). By curling up, trilobites protected their soft abdomen. Ordovician period of the Leningrad region. Photo by A. Bronnikov.

Fossilized remains of trilobites are exported in large quantities from the Leningrad region. The picture shows collectible pieces prepared for export to Germany.

Trilobites of the genus Asaphus in the rock. Ordovician period of the Leningrad region. The flattened wide shell of the trilobite Ptychopyge indicates that it probably led an inactive (crawling) lifestyle. Photo by A. Bronnikov.

Representatives of the species Asaphus kowalewskii have eyes raised on long stalks. This allowed them to dive deep into bottom sediments in search of food and at the same time observe the appearance of enemies. Ordovician period of the Leningrad region. Photo by A. Mazin.

Trilobites of the genus Asaphus had a thick-walled, convex shell with a smooth surface. This indicates that they were constantly digging in the ground.

Trilobites settled across vast expanses of the ocean in the form of small planktonic larvae. In some Cambrian localities of Yakutia, these larvae are found in large quantities.

Most modern arthropods have well-developed eyes. They can be simple (with one or two lenses) and complex or faceted, consisting of several dozen, hundreds or even thousands of simple eyes. Paleozoic trilobites had the same eyes. The visual surfaces of trilobites' enormous compound eyes were oriented in such a way that many of these animals could see 360 ​​degrees around them at once. But only along the horizon line and one or two ten degrees above it. To observe the “dead” space at the zenith, a small single peephole was located in the occipital part of the trilobite head shield.

The eyes of some species of trilobites, which searched for food by burrowing into the upper layer of silt, were raised on long stalks, like those of modern crustaceans and gastropods. But unlike them, trilobites could not retract their eye stalks into their heads, rotate them, or fold them. The eyestalks of trilobites are hard outgrowths of the shell, and they always stood upright and therefore, of course, were in danger of being broken. But they still broke very rarely. Of the hundreds of shells I have seen of the trilobite Asaphus kowalewskii, which probably has the tallest eyes, I found only one specimen with a stem broken off during life.

All limbs (and trilobites have several dozen of them), like the rest of the abdomen, were soft and therefore are preserved in a fossil state only in exceptional cases. For the first time in Russia, a trilobite with preserved limbs was found in Yakutia three years ago.

The chitin of arthropod shells cannot stretch. Therefore, their growth is accompanied by several molts. When the shell becomes tight, it bursts (usually on the front and back) and the animal throws it off. In that short period when the old shell is shed and the new one has not yet hardened, the size of the animal quickly increases. The posture in which the “hatching” from the old shell occurs is very characteristic and varies among different species of trilobites. For a paleontologist, it is very valuable to find a shell in a “molting position,” because this indicates that the rock where it was found was not processed by burrowing animals or mixed by some other forces. This means that here you can see the details of the rock formation process, you can restore the environmental conditions at the bottom of the ancient reservoir in which trilobites lived.

The variety of forms of the trilobite shell is striking: smooth, lumpy, spiky, with huge and reduced eyes, low or raised on long stalks, with long branching outgrowths, with a body consisting of two segments or several dozen, and so on. It is known that the shape and degree of dissection of the shell in arthropods are associated with their internal anatomy, indicating the preferential development of certain muscle groups. All this allows us to judge the lifestyle and nutritional patterns of animals.

Those species that slowly crawled along the surface of the bottom had a flat, wide shell. Convex with deep grooves - for those who actively moved along the bottom and buried themselves in the ground. Convex, thick-walled with a smoothed surface - in those species that constantly burrowed in the ground. From the shells of some trilobites it can be understood that they led a planktonic lifestyle. They have small body sizes and huge eyes, and when folded, large unprotected holes remained on the sides of the shell - the exit points for long swimming limbs.

Dozens of species of trilobites with shells of various shapes could live in the same place. This means that their diet and lifestyle were very different.

Previously, it was believed that trilobites (except for planktonic species) could only feed by swallowing the top layer of soil rich in organic matter, since they had soft limbs that seemed not adapted to grasping prey. Recently, new evidence has emerged showing that some species of trilobites were undoubtedly predators. This is evidenced by a find in Sweden. Traces of some animals living in the soil and traces left by trilobites were found there. In this case, the trace of the trilobite covers the trace of an animal living in the ground, and it breaks off. Consequently, trilobites of this species searched for and ate animals that lived in the ground. Trilobites with preserved intestinal contents were found in Yakutia. Particles of the bodies of benthic animals - sponges and brachiopods - were found in it.

Like many marine arthropods, trilobites in their development passed through the stage of planktonic (that is, passively floating in the water column) larvae. It was thanks to their small larvae, which looked completely different from adult animals, that trilobites were able to settle over vast areas of the Paleozoic oceans.

Remains of trilobites are found in many places in Russia, where Paleozoic and especially ancient Paleozoic marine sediments emerge on the surface. The most famous of them are in the Leningrad region and in Eastern Siberia (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, fossilized remains of trilobites are found in smaller quantities. But among them there are many that amaze with their excellent preservation. Many shells have retained their original shape and are usually a beautiful chestnut-brown color. It is given to them by the residue of incompletely decomposed organic matter. In places where the shell thickens (where there was more organic matter), dark spots are visible, and, for example, the visual surface of the eyes remains colorless and transparent. There is a known case when the lifetime coloring was preserved on the shell, namely the coloring, that is, the pattern, and not the color.

Features of the search and extraction of trilobite remains depend on the type of location. Soft clayey limestones of the Leningrad region are destroyed more easily in the open air than the shells of trilobites. Therefore, as soon as the layer is exposed, trilobites begin to “peek out” from the rock. But here fossilized remains are found rarely and at a great distance from one another. In Yakutia, hard, coarse limestones are almost indistinguishable in color and mechanical properties from the trilobite remains they contain, and visual inspection of outcrops here usually yields nothing. But when fossils are discovered, they are usually numerous and evenly distributed throughout the rock.

The search and collection of trilobites is carried out by methodically sequentially crushing large blocks of rock layer by layer.

To separate the found shells from the rock, various pneumatic and vibrating tools are sometimes used, but most often they work with an ordinary steel needle. The work is long, painstaking, requiring patience and accuracy.

Trilobites from the Leningrad region, due to their aesthetic qualities and relative ease of extraction, have now become one of the main export objects of paleontological remains from Russia. The interest of collectors in them is very great, this, of course, is good, but it is also associated with many troubles. Intensively mined outcrops quickly become impoverished, if not completely destroyed. Collectors usually have a barbaric attitude towards unique fossils, since they are only interested in the completeness of the extracted shell. In this case, science irrevocably loses the opportunity to obtain very important information about the sequence of occurrence of species in layers and about the accompanying fauna. And sometimes the morphology of trilobites is distorted, since it happens that collectors replace missing fragments with parts of the shells of trilobites of other species, or even simply mold them from plastic.

However, in the modern fauna there is a group of arthropods that are surprisingly 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; only thick antennae consisting of large segments are visible. Isopods, like trilobites, have the ability to roll 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 relatedness (in general, quite 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 occupied the vacated niche of extinct trilobites.

Originating at the very dawn of the Paleozoic era, trilobites(Trilobita) quickly mastered the Angarida seas. Until their disappearance in the Permian, they remained purely marine animals. Their ancestors may have been some primitive worm-like creatures, but in general the sudden appearance of these highly organized creatures in the arena of life is mysterious. After all, their structure turned out to be so perfect almost immediately that it allowed trilobites to exist for almost 340 million years, giving rise to a huge number of species.

In the course of evolution, nature offered the living creatures of the Earth two versions of the skeleton - external and internal.

Trilobites implemented an external option.

Their skeleton was a durable chitinous shell, longitudinally and transversely divided into three parts, from which the name comes: trilobites - “three-lobed”.

The growth of trilobites was always accompanied by molting.

Growing individuals shed their shells in exactly the same way as modern crayfish do. Therefore, the discovery of a large number of remains of fossil shells does not mean that huge numbers of trilobites lived in this particular place. Most likely, this section of the sea was convenient for carrying out a rather complex and important procedure - changing the “clothing” that had become too tight for the body. Then, falling into the sediment, the chitinous substance of the shell was replaced by inorganic components. Most often it was carbonate in the form of limestone, less often - pyrite and silica. Hence the excellent preservation of fossils.

The trilobite's shell consisted of several hard parts, securely connected by special membranes during life. It was divided longitudinally into a central and two lateral parts, and transversely into a head shield ( cephalon), torso ( thorax) and tail shield ( pygidium).

The head shield was a rigid formation, divided by sutures into a central part ( cranidium) and two side ones - movable cheeks. The preoral plate also belonged to the cephalon ( hypostome) on the ventral side. The body itself was covered with many hard segments, connected (of course, in living individuals) by thin movable membranes.

The belly of the trilobite, like its limbs, was covered with a thin chitinous cover, which quickly collapsed after molting. This cover can be observed only on those specimens that were suddenly buried by thin silty sediment and were well preserved.

Longitudinal sections of well-preserved specimens along their axial line allowed researchers to identify the shape of the digestive tract of trilobites, and similar cross sections in the area of ​​the head shield revealed the “liver” outgrowths of the intestines.

The places where muscles are attached to the shell are clearly expressed in fossils with special spots and grooves. By their depth one can judge the activity of a particular muscle system. In well-preserved specimens it is sometimes visible that one of the branches of the upper limbs bears a weak brush of tightly fitted outgrowths. This structure apparently functioned like gills.

Many trilobite species had well-developed eyes.

This, by the way, indicates that trilobites had a fairly complex nervous system and its central organ - the brain.

Studying the Silurian trilobite suborder phacopine(Phacopina), English researcher Clarkson came to interesting conclusions.

The complex eyes of phakopins, which had a circular view, consisted of numerous facets collected in rows. Each facet capped the outer end of a tiny cylinder that transmitted light down to the light-sensitive cells. After making a comparison with the eyes of modern arthropods, Clarkson came to the conclusion that, despite all the complexity of the structure, the eyes of trilobites were still not organized enough to clearly perceive the shape of objects. The division of the visual field into visual stripes allowed trilobites only to perceive horizontal movements of objects and approximately determine their size, speed and direction of movement. That is, they perceived the approach of an object, drawing conclusions from the fact that it was registered by higher and higher facets of their protruding eye.

However, other of the same phacopoid trilobites had biconvex lenses instead of facets. There are many such lenses. It is possible that, thanks to this, their vision was no longer different from ours, and their visibility, perhaps, surpassed it.

Trilobites were bisexual organisms.

The female apparently left the eggs in a lightly sprinkled hole. The “nest” quickly filled with loose sand, but the male, following the female, of course, managed to fertilize them. The water supplied the eggs with oxygen dissolved in it, and later helped the larvae to emerge. In fossil material, although not often, all these transformations can be traced - from egg to adult organism. At the same time, it is clearly visible how the head shield was formed at an early stage of development. First, its axial part (glabella) was separated. Then it showed primary segmentation in the form of five rings and, finally, at the final stage of the first stage of development - a tail shield. Well, at the second larval stage, the body segments were formed.

With the appearance of the last segment, the trilobite entered the adult stage of its existence. Subsequently, only the growth of the animal occurred, without the appearance of any new structures in the skeleton.

Having reached a clear discrepancy between the size of the soft parts of the body and the size of the shell, the trilobite began molting. He actively sought to free himself from the tight “clothes” that had become tight. The seams of the head shield - front, edge, transverse and all others, along which the connections of adjacent parts of the shell passed, were weakened. Now the trilobite could throw off these parts of the shell with a sharp shake of its head. He simply crawled out of the rest of the “clothes”.

Not a very aesthetic way, of course, but... convenient!

Trilobites of the warm seas of the Angarides were very diverse.

Among the species described by paleontologists there were dwarfs - a few millimeters in length, and giants - up to half a meter in length. Some tail shields had a short axial part and a fan-shaped arrangement of lateral ribs, while others had the ratio of these elements ordered by segments.

There is no doubt that the chitinous cover of trilobites was painted in different colors. At least, researchers have more than once noted a completely distinguishable striped and dotted pattern of some forms.

Fossilized trilobites are always very attractive, but it is unlikely that a person would feel comfortable among these strange creatures. Too different worlds, too vast times separate us.

Trilobites lived in shallow waters.

This was their element - the seabed and shallow bottom layer of water. They were probably unimportant swimmers, but most importantly, they already knew how to move through the thickness of sea waters, patiently looking for places with better lighting, richer in food, and calmer ones. It is possible that very small forms led a planktonic lifestyle, surrendering to the will of currents, while the blind ones lived in deep or highly turbid seas, where almost no sunlight reached.

At first, all trilobite species were most likely vegetarians. Their food was algae growing in the form of a layer of mucus on bottom stones and on a hard coastal substrate. This is clearly evidenced by the strongly convex and expanded anterior part of the digestive tube, the so-called glabella, capable of accepting a significant volume of organic-enriched sediment. Lovers of animal food appeared among trilobites much later. But they appeared. This is evidenced by deep glabellar grooves of many species - all the same places of attachment of muscles that move the jaw apparatus.

Of course, it is unlikely that trilobites, given their not too great mobility, were real predators. Most likely, they ate the corpses of, say, dead jellyfish. Many mass burials of jellyfish are known in Precambrian deposits, but later such burials are practically never found. It is possible that trilobites are to blame for this, having learned to feast on the remains of their neighbors in the ancient seas.

During the Cambrian period, trilobites populated the entire world shelf and reached the maximum number of species. This was undoubtedly facilitated by both the favorable habitat and the complete absence of predators. Only with the advent of cephalopods, and then fish, which had a lot of good teeth and a lot of bad intentions, did trilobites have to look for effective means of defense.

One of these remedies turned out to be coagulation.

By curling up into a kind of chitinous ball, the trilobite protected its most vulnerable part - the soft abdominal membrane. At the same time, “decorations” in the form of thorns served a protective function. All those cheek protrusions and spiny protrusions along the front and back edges of the shell really made it difficult for predators to grab their prey.

Whether the development path of trilobites was progressive is a controversial issue, especially since by the end of the Paleozoic they all died out, but the huge diversity of forms, that is, high variability, allowed trilobites to remain the most prominent group of organisms in the early seas of the Earth for hundreds of millions of years.