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The heyday of trilobites occurred in. Trilobites. Stone-eyed creatures. Internal organs and reflexes of the body

Morphology

The body morphology of trilobites fully corresponds to the organization of the type of arthropods, however, they have features of similarity to the type of annelids (in particular, their body consisted of many homogeneous segments). The body structure of trilobites bears evidence of adaptation to the bottom lifestyle: a powerful shell, flattening, compound eyes on the upper side of the body, the location of the mouth and legs on the ventral side of the body. Among the trilobites, some groups fed on silt, others on small invertebrates, and some on plankton. Many trilobites were likely carnivores despite the lack of jaws. To grind food, they were served by modified appendages on the bases of the limbs (gnatobases). There were free-swimming, crawling and burrowing animals.

The body length of trilobites reached 90 cm. The body consisted of an integral head and a segmented body. The limbs of trilobites are multifunctional, that is, they performed several functions at once - motor, respiratory and chewing. In some trilobites, the organs of touch are distinguishable - antennae on the head.

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

Trilobites developed with metamorphosis. Their fossil eggs and larvae have survived. Evidence has been preserved that trilobites moulted successively, and after each molt their trunk increased by several segments.

Trilobite shell structure:
I- head section (shield)
II- trunk region (thorax)
III- tail section (pygidium)
1 - face seam
2 - movable cheek
3 - buccal acumen
4 - glabel
5 - occipital ring
6 - fixed cheek
7 - eye
8 - rachis (axial part of the shell)
9 - pleura (lateral parts of the shell)
10 - dorsal groove
11 - tail segments
12 - thorn (telson) © Muriel Gottrop

Rusophycus, fossil traces of crawling trilobites

A significant part of the fossil finds of trilobites fall on the dorsal shells, which animals shed during molting and on which there is no movable part of the cheek. Less often, unknown parts of the skeleton are found in fossilized form: limbs (legs) and tentacles. In addition to fossils, trilobites have left numerous traces of life, including resting (Rusophycus) and crawling (Cruziana and Diplichnites).

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

  • head shield with two well-developed eyes for the most part;
  • trunk (thorax), consisting of a different number of movably connected segments;
  • tail shield (pygidium), which differs from the body in that its constituent segments are motionlessly interconnected.

In addition, by two longitudinal, almost parallel dorsal grooves, the shell is subdivided into three lobes: the middle and 2 lateral ones. From this subdivision comes the name "trilobites" ("three-bladed").

Many trilobites had the ability to fold 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 glabella, the lateral lobes are called cheeks; the posterior corners of the cheeks are often extended into more or less long cheek points. The head shield rarely consists of one inseparable part, but usually it is divided using special lines or so-called. seams into several separate parts, along which, after death and during petrification processes, the head shield often disintegrated. These separate parts also include a special plate on the twisted part of the shield, the so-called hypostome (or upper lip), which probably served as a cover for the abdomen. The body splits into a middle, or axial, part (rachis) and lateral parts (pleura), while on the caudal shield, as in the continuation of 3 corresponding parts of the body, an axial lobe and lateral lobes are distinguished. The axial parts of the body and caudal shield in the fossilized state are open from below, since they were covered during life with a thin skin, but the lateral parts have preserved a hard curvature, which is usually distinguished by special lines decorating it. The appendages of the abdominal side, recently discovered, consist of: 1) of four pairs of limbs above the head shield on the sides of the oral opening, consisting of 6 - 7 segments and serving as part of the chewing organs. The end members of the posterior pair were in the form of swimming blades; 2) from paired bifurcated limbs, located both under the trunk and under the tail segments, consisting of a number of segments ending in claws. Above the outer branch, there were also special bifurcated and spirally folded appendages, considered as gills. According to Beecher's research, in front of the mouth is a pair of long, thin, segmented antennae, which are still open in very few trilobites (Triarthrus).

Sense organs

Trilobites possessed faceted eyes, which were planted on stalks in those animals that buried themselves in the mud. Representatives of the order Agnostida are completely devoid of eyes, which, apparently, is associated with life at great depths or in muddy water. According to 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 against each other, 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 shell 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 the size of the lenses.

Spreading

The number of trilobites is quite large. Even Barrand counted them over 1700 species, of which 252 belong to the Cambrian period, in the Silurian period: 866 to the Lower Silurian, 482 to the Upper Silurian epochs, 105 to the Devonian and only 15 to the Carboniferous period; only 1 species passes into the Permian.

The job of classifying trilobites was difficult for paleontologists. It turned out that one cannot proceed from any one feature, but many features must be taken into account 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, moreover, the ability to coagulate is still poorly developed in them. In the Lower Silurian, the group Asaphidae... They have a constant number of body segments 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 of 13 and the eyes have a peculiar appearance. In the Upper Silurian system, groups Proetidae, Bronteidae, Calymenidae that pass into the Devonian system; in the Carboniferous system, only representatives of the Proetidae are found.

Particularly well-preserved remains of trilobites are found in the Yunnan province in China (Maotianshan shale), in the province of Alberta in Canada (Burgess shale), in the state of New York in the USA, and in the Rhineland-Palatinate in the Federal Republic of Germany (Hunsrück shale).


see also

Literature

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

Notes (edit)

Links

  • Illustrations of Ordovician trilobites in the environs of St. Petersburg. Archived
  • E.B. Naimark. The emergence of homologous series in the centers of diversification (on 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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  • Arachnids

See what "Trilobites" are in other dictionaries:

    TRILOBITES- (Trilobita), a class of extinct pestilence. arthropods. T. are already known from the deposits of the Early Cambrian seas, reached their heyday at the end. Cambrian Ordovician and became extinct by the end. Paleozoic. L. from 10 mm to 80 cm. The body is segmented, flattened in the dorsal abdominal ... ... Biological encyclopedic dictionary

    TRILOBITES- marine crustaceans fossil animals, found mainly in the Silurian formation. Extinct by the end of the Devonian period. Dictionary of foreign words included in the Russian language. Pavlenkov F., 1907. trilobites (group tri ... three ... + ... ... Dictionary of foreign words of the Russian language

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

    TRILOBITES- a class of extinct marine arthropods. Lived in the Cambrian mid-Permian. St. 10,000 species were widespread in shallow waters. Body length from 1 to 80 cm (usually 3-10 cm). Leading Fossils ... Big Encyclopedic Dictionary

The remaining nine orders belong to the subclass of multi-segmented 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, the anatomical features of the structure of the bodies of adults play a huge role. However, such a classification does not allow us to accurately classify all samples of fossil trilobites studied at the moment.

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

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

Sample photos

Anatomy:

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

Carapace fossil trilobites are composed of three layers of chitin saturated with calcium salts. The total thickness of the chitinous layers of the shell usually does not exceed 1 mm. Different types of trilobites have different shells, they can have a porous structure, be smooth or have a sculpture (growths or thorns).
In some species of trilobites, the three-lobed structure of the shell may be poorly visible (lost / erased) (rachis is not observed or is poorly expressed), which, according to scientists, may be associated with the burrowing way of life of these trilobites (for example, in the genus Bumastus).

Cephalon trilobite, i.e. its head is usually semicircular. The cephalon consists of glabella and fixigena, collectively called cranidium. On the right and left sides of the cranidium, there are librigena (librigena), right and left, respectively.
- 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, segmentation is observed only in the glabella, but not always (in most cases, the glabella has furrows on the sides or has a completely smooth shape). The number of glabella furrows is different for different representatives of the trilobite class;
- The occipital ring is usually located behind the glabella, which in shape often resembles the rings of rachis;
- Librigenes are also called free or mobile "cheeks" of trilobite;

The face suture is the junction of the cranidium with the librigens;
- In sighted species of trilobites, the eyes are located on the cephalon under the eye lids. Read their detailed description below;
- In some species of trilobites, the eye ridges extend from the glabella to the eyes, often passing into the eye lids;
- According to research data, the muscles of the head extremities were attached to the inner side of the glabella in trilobites, as well as the internal organs (stomach, heart and brain) were located;

Presumably, some types 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 in some trilobites of pits taken by scientists for traces of attachment of bristles, these pits are larger than the pores of the trilobite shell.
The trilobite cephalon can also be called the head shield.
Head cheek spines can be located on fixigen and librigens.
For a detailed description of the cephalon and buccal spines, see the figure:

Types of facial sutures: depending on where the back branch of the facial suture crosses the edge of the head shield, there are four types of facial sutures (highlighted in bold lines in the image below):
1) proparium type (A, B, C);
2) opistoparium type (D, E, Z, I, K);
3) gonatoparium type (F);
4) metaparium type (L).

Thorax, i.e. the trunk of a trilobite consists of a number of movable-articulated segments that allow the trilobite to bend and take a folded form in case of danger (like modern woodlice). The thorax separately, 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 rachis, and the segments of the pleural lobe are called pleura. The pleura along the edges of the trilobite are bent into the abdominal region, forming a double (volvulus).
Different types of trilobites have a different number of dorsal segments (from 2 to more than 100). Most trilobites have 8 to 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 articulated bifurcated 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 the figure in different colors:
- in the axial lobe of the segment there is an articular half-ring (green), which is located under the superior segment. The semicircle is usually hidden under the segment in front; it can be seen only in coiled trilobites or after the destruction of the trilobite 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 provide its flexibility;
For a detailed image of the thorax and separate dorsal segments, see the figure:

Pygidium (pygidium), i.e. the tail shield is the end (rear) of the trilobite. Pygidium performs a protective function: in case of danger, the trilobite folds, and its posterior part (pygidium) merges with the anterior part (cephalon), as a result of which the trilobite takes on a rounded shape (like modern wood lice). Like the thorax, the pygidium of the trilobite consists of a different number of segments, each of which has a pair of articulated two-branched limbs in the ventral part. In contrast to the movable 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 (just like 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 types of trilobites have different number of segments (from one to 30).
By their relative size, four types of pygidium are distinguished:
1. Micropygidium - the pygidium is smaller than the cephalon;
2. Almost standard pygidium (subisopygous) - a pygidium of practically the same size as a cephalon;
3. Standard pygidium (isopygous) - the size of the pygidium is equal to the size of the cephalon;
4. Macropygidium (macropygous) - the pygidium is larger than the cephalon.
Possible ratios of pygidium with 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-like plate that connects to the rostrum (rostral plate) in the ventral portion of the cephalic 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 from the ventral side: the brain, stomach, intestines; as well as the mouth of a trilobite. Most hypostomes are located at the same level with the glabella (floating hypostome and adjacent hypostome), i.e. The hypostome is located directly under the glabella on the opposite side of the cephalon (head). However, it happens that the hypostome is not located on the same level with the glabella (impending hypostome).
In different trilobite species, the hypostomes look different, this can help in classifying the trilobite species. A detailed study of the hypostome can also show how and what a given species of trilobite ate.
In isolated cases, trilobites retain the so-called lower lip - postpartum metastoma having a convex shape.
In addition to the hypostome and metostomy, the rostrum (rostral plates), a pair of antennae, and four pairs of limbs are located in the ventral part of the cephalon (head) of the trilobite.
The edge of the trilobite shell bends down and forms a strip of various widths in the ventral side of the cephalon, thorax and pygidium, this strip is called a doubler (volvulus).
A detailed description of the abdominal part of the trilobite and the variety of the hypostome are shown in the figure:

Eyes Trilobite is a very complex mechanism made up of many lenses. There were blind trilobites such as Ellipsocephalus hoffi. They, according to scientists, lived at great depths, where light did not enter, 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 (fixigena) in the head of a trilobite (cephalon). The trilobites Asaphus kowalewski and Cybele panderi had eyes on the stalks, which allowed them, buried in the silt, 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 very 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, pp. .25-26).
There are three types of trilobite eyes:
1. Faceted eyes of the "Holochroal" type (holochroic eyes) - contained from 100 to 15,000 small lenses. Biconvex or prismatic lenses are usually hexagonal and sometimes quadrangular. All lenses were in direct close contact with each other and had a common stratum corneum. The sclera (albuminous membrane) was absent between the lenses. Most members 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 rounded 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 were matched to the size of the lenses.
For detailed photos of trilobite eyes, see the picture:

Trilobite limbs
Like modern arthropods, trilobites had articulated limbs, i.e. limbs consisting of members connected to each other. These limbs were located on the ventral side and were bifurcated (branched at the base). The number of limbs varied among different trilobite species. Each segment of the thorax and pygidium had a pair of bifurcated limbs in the ventral part (as shown in the figure below). The cephalon had five pairs of bifurcated limbs in the abdominal part (the first pair were antennae attached to the hypostome; and the next four pairs of postpartum limbs). In different genera of trilobites, the antennae differed in the length of their constituent members. The antennas are attached to the hypostome in small recesses. And the postpartum limbs participated in the process of capturing food and moving it into the mouth opening. The limbs of different trilobite segments practically do not differ from each other. The limbs of trilobites of different genera and species have minor differences.
In trilobites of the genus Olenoides, a pair of filamentous limbs were found located at the end of the pygidium (similar limbs can be observed in modern shtitti), possibly the same limbs were present in other genera.
It is very rare to find preserved (fossilized) limbs of trilobites, as they were very fragile compared to the shell of trilobites.
The most famous trilobites with extant limbs are pyritized trilobites, which are found in a quarry near the city of Rome (Rome), New York, USA (coordinates: + 43 ° 15 "12.00", -75 ° 24 "30.00").
All bifurcated limbs consisted of three component parts:
- coxopodite - the base of the limbs;
- exopodite - a branch of a limb, consisting of a thin segmented axis, equipped with villi. According to scientists, exopodite performed respiratory functions;
- endopod - a branch of a limb, consisting of eight different members. Endopodites were the limbs designed for the movement of trilobites, and the endopodites of the cephalon, according to scientists, had the function of capturing and grinding food.



GROWTH OF TRILOBITE AND MOLD
Since the trilobite had an external chitinous skeleton, the growth of the trilobite's body occurred only during molting (the discarding of the old exoskeleton), like in many modern arthropods.
The junction of the fixigen and the librigen is called the facial suture. During molting, the old shell of the exoskeleton ruptured along the line of the facial suture, after which the fixigen shell was sometimes completely torn off. Since the facial sutures run near the eyes, the trilobite's eyes were the first to be released during molting. Further, through the formed hole, the trilobite left the shell of the old exoskeleton.
Most of the fossil trilobites are exoskeleton shells shed during the molt of trilobites. The molting process explains the reason for the frequent finding of incomplete trilobite specimens (body with pygidium, but no head, or only a single pygidium).
Video example of molting of modern arthropods:
http://rutube.ru/tracks/5559771.html
http://rutube.ru/tracks/4226503.html
For a detailed picture of the trilobite molting process, see the figure:

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


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ROLLING TRILOBIT
In a dangerous situation, the trilobite, for defense purposes, could take the shape of a ball, folding like modern wood lice. When folding, the flexible back flexed, and the pygidium was connected to the cephalon. This form of self-defense helped to preserve the limbs (members) and the soft abdomen. Often, fossil trilobites are found rolled up. This indicates that the sample found is the trilobite itself, and not the shell (exoskeleton) shed during molting.
The ability of the trilobite to fold is a passive defense against enemies.
A huge role in the folding function is played by pandera organs... Pandera organs were first discovered in 1855 by the Russian academician S.N. Pander, later A. Folbort in 1857 gave the name to these organs - "Pandera organs" in honor of their discoverer.
These organs are located on the duplicate of the buccal edges and on the duplicate of each segment of the trunk. Pandera organs differ in different types of trilobites. According to research by E.A. Balashova (1955), the tubercles of the Pandera organs play the role of "locks", i.e. when the trilobite is folded, these "locks" close and the trilobite does not need to use muscles (keep them in constant tension) to maintain the folded shape. Also, according to E.A. Balashovoy holes in Pandera's organs play a respiratory function at the time of trilobite coagulation - through them, water can continuously penetrate under the trilobite's carapace to the gills, which allowed the trilobite to be in a coagulated state for a fairly long time.
Photos of the folded trilobites:


There are three types of folding of trilobites (according to the PIN RAS) are 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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NUTRITION OF TRILOBITES
According to scientists, different types of trilobites ate differently. Among the trilobites were predators, scavengers, possibly herbivorous and possibly filtering (filtering water, i.e. planktivorous).
According to the results of the research, scientists suggested that trilobites with a conterminant-type hypostome (adjacent hypostome) were predators. Trilobites with a natant-type hypostome (floating hypostome) were omnivores (carnivores, scavengers, and possibly algae).
Some trilobites (for example Cryptolithus) had a specific head shape with pore holes, which allowed them to easily filter water through these holes. They, according to scientists, were filtering trilobites (an example of a filtering model is shown in the description of trilobites of the order Harpetida).
The trilobites Asaphus kowalewski, which had eyes on the stalks, were, according to scientists, a predator. The trilobite of this species buried itself in the soil so that the eyes remained on the surface. In this state, he waited for the victim and, when the opportunity arose, attacked.
Blind trilobites (eg Ellipsocephalus hoffi) were unable to hunt due to their 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 eodiscid trilobite egg laying in 1994. Now scientists suggest that some species of trilobites laid eggs in the preglabel lobe of the head part (cephalon), where the brood bursa formed in which the young developed later. This type of reproduction is inherent in modern horseshoe crabs, which are also representatives of arthropods. However, in some species of fossil trilobites, no such brood bursa has ever been found. According to scientists, their eggs could be laid under the cephalon, in its lower part, slightly above the hypostome.
The presence of a brood bursa is an example of sexual dimorphism in trilobites (the difference between males and females).
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 sex 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 sex difference 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 trilobite:
1) an egg (the size of trilobite eggs ranges from 0.6 mm to 4 mm);
2) development of the larva;
3) an 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: the larva is about 1 mm in size, the eyes are absent, the body is a scutellum, which is a single whole (undivided into the 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: there is a division of a single shield (body) of the trilobite into the head and tail shields; pleural spines appear; one after another, segments of the thorax (trunk) of the trilobite appear until they reach the maximum number (characteristic of the adult forms of trilobites). New segments of the thorax appear in trilobites as they grow, forming between the last segment of the trunk and the caudal shield.
3) Holaspis: the larva is small, 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 fossilization. However, such cases have been recorded.
In the head part of the trilobite, between the hypostome and the 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 trilobite glabella, the larger the stomach underneath it. On the sides of the stomach were associated with the stomach hepatic processes, which are branched fine wrinkles, radially diverging from the glabella to the outer edge. Sometimes these hepatic processes are called diverticula of the stomach.
Heart was located above the alimentary canal and was a long multi-chamber vessel.
Also in the head of the trilobite is brain which is the center central nervous system organism (central nervous system). 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 CNS itself of trilobites is the abdominal nervous system. passes through the entire abdominal part of the trilobite from cephalon to pygidium. CNS has never been found in trilobite fossil specimens. According to scientists, the central nervous system consisted of one or two nerve trunks with segmental ganglia(swellings) corresponding to the trilobite body segments.
Of great interest to science are also pandera organs which are described above in the section "Collapsing of the trilobite", these organs were necessary for the trilobite to stay in the collapsed state for a long time.

Find Locations:

1. Australia South, 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 province, Maotianshan and other settlements near Chengjiang.
6. Morocco, Antiatlas mountains.
7. Russia, Leningrad region: the valley of the Volkhov river; Putilovsky quarry; the Vilpovitsa quarry; the valley of the Lava river and other places.
8. USA, California, San Bernardino, Marble & Providence Mountains, Latham Shale.
9. USA, New York, Middleport, Khalevov quarry, Rochester Shale.
10. USA, New York, Herkimer County, Trenton Falls, Walcott-Rust quarry.
11. USA, Ohio, Sylvania.
12. United States, 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 places of finds are indicated)

Habitat:

Trilobites were benthic marine inhabitants (benthic, i.e., living on the bottom). Some trilobite species (Ellipsocephalus hoffi) were devoid 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 silt so that only eyes were on the surface. According to scientists, some species of trilobites may have been able to swim and their habitat was floating algae (floating forms of trilobites are also called pelagic, that is, living in the water column).

1. History. Trilobites were first described by Llwyd in 1698, when they were named Trinuclei. Some of the 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. A variety 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 the massive extraction of trilobites is carried out, new species are constantly being discovered.
According to the resource trilobites.info, the Trilobita class includes 10 orders, 17 suborders, 32 superfamilies, 170 families, and 3944 genera (species abundance is unknown).

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

4. Chitin(translated from ancient Greek - clothes, shell, skin), which made up the exoskeleton of trilobites - a natural compound from the group of polysaccharides, is part of the cell wall of bacteria and fungi. Chitinous exoskeleton often "impregnated" with a variety of 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 found in Canada (Mantiba), its length is 72 cm. Now this trilobite is in the Museum of Man and Nature in Winnipeg (Mantitoba). Large trilobites are very rare and usually 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 believed to be the first to explore trilobites in 1698. After him, the trilobites were explored by Linnaeus in 1745 and Walch in 1771.
Trilobites were first classified 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, the study of trilobites was carried out by: Pander, Eichwald, Möller, Holm, F. Schmidt, V.N. Weber, E.V. Lermontov, N.E. Chernysheva, N.P. Suvorov, 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. Maximova, O. G. Tumanskaya;
- In Czechoslovakia and France, trilobites were studied by: Barrande, Beyrich, Corda, Oehlert;
- In England, trilobites were studied by: McCoy, Salter, Woodward, Reed, Lake, Row;
- In Germany, the study of trilobites 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, trilobites were studied by: Hall, Walcott, Matthew, Raymond, Resser, Rasetti;
- In Asia, trilobites were studied by: Walcott, Mansuy, Reed, Kobayashi, Sun Y.C. Lu Yen hao;
- In Australia, Whitehouse was involved in the study of trilobites.
(according to the book "Fundamentals of Paleontology. Volume 8. Arthropods. Trilobites and Crustaceans" 1960)

7. Trilobite shell color. Usually, in fossil trilobites, the color of the shell is even, uniform. However, there have been rare cases of detection of lifetime color of the shell of trilobites. The striped and spotted colors of the trilobites Anomocare, Isotelus, Proetus are described.
An article on 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, which are also representatives of arthropods, the larva has a shape resembling a trilobite. This fact was the reason for assigning the name "trilobite larva" to it.

9. Scientific films about trilobites. We could not find a full-fledged scientific film only about trilobites, but there are several films in which trilobites are given worthy 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 on 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 collections can be found at http://www.trilobitejam.com/

11. Trilobite images. Notable images of trilobites:
- The municipality of Murero, Campo de Daroca region, Caparoca province, Aragon Autonomous Community in Spain has a coat of arms depicting a trilobite. Murero is renowned throughout the world as the "Sistine Chapel of the Trilobites".
- In the center of the coat of arms of the English (England) city of Dudley (Dudley) depicts 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 also bears the modern electronic robotic vacuum cleaner "Trilobite", manufactured by Electrolux, which has a partial resemblance to fossil trilobites.

14. Sculpture-trilobite on wheels... Sculptor Jon Sarriugarte teamed with sound effects master 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 joystick control in the head, headlights and underbody lighting for night trips.

15. Trilobite Restaurant. 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. A 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 dog-sized trilobites appeared, which killed in turn all the workers of the station. Throughout the film, oil production workstations 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 toy. One of the heroes of the Japanese anime series "Bakugan" ("Bakugan") - Limulus (Limulus) - this Bakugan is named a trilobite, although it looks more like a horseshoe crab. Quote: "Limulus is a trilobite-like Bakugan, with very dangerous spikes on its back. Intimidating tentacles can wrap around Limulus opponents, rendering them helpless. Lumulus uses the enemy's power to augment his own." (http://www.bakugan.com.ua/collection_bakugans_core_L.php)
Trilobites also served as the prototype for the creation of the hero of the anime "Pokemon" ("Pokemon") under the name Kabuto (a mixture of trilobite and horseshoe crabs). (http://wiki.pokeliga.com/Kabuto). Kabuto was featured in three episodes of the anime: Episode 13 "The Riddle of the Lighthouse", Episode 46 "Attack of Prehistoric Pokemon" 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 German Democratic Republic "Paleontology", issued on 06.02.1973, where a trilobite is depicted on the stamp with stomy 70Pf (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 the image of trilobites;
- one Finnish stamp of 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 uploaded a prefabricated paper model of a trilobite that can be printed and assembled at home using scissors and stationery glue.
You can download the file from the Houston Gem and Minetal Society website: http://www.hgms.org/Paleo/trilobite-model.html
Or by 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 language... The word Trilobite in Japanese sounds - "SaYoMushi" ("sayomushi" or "sayomushi") and consists of three characters: "san" - three, "yo" - a leaf, "mushi" - an insect. Literally from Japanese, this word can be translated into Russian as "three-leafed insect".

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

23. Tolkien and the trilobites... One of the genera of fossil trilobites from the Acastidae family (superfamily Acastidea / suborder Phacopina / order Phacopida) was named Tolkienia in honor of John Ronald Reuel Tolkien. The genus was described in 1997 in 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.

Introduction

Our story will go in particular about trilobites, and an inquisitive reader will learn a lot about their habits and history.

Trilobites are a class of marine arthropods that are widespread in the Paleozoic seas and became extinct at the end of the Permian. Of the living animals, the closest relatives of trilobites can be considered horseshoe crabs, but they are also distantly related to these ancient creatures.

Trilobites have attracted the attention of many people - paleontologists, evolutionary biologists, collectors, and filmmakers. This is an incredibly successful group in terms of evolution. Keeping the general plan of the structure, trilobites were able to master many ecological niches and survive for more than 300 million years.

For today, we will leave aside the usual study of fossils and computer reconstructions. In order to get acquainted with the heroes of our story, we will go back in time to the Silurian period.

Silurian

So, 430 million years BC, Southern Hemisphere, the coast of the supercontinent, Gondwana. An endless ocean stretches to the very horizon, and somewhere in the north, its waves break on the shores of Laurentia, the Baltic and Angarid - other continents of this young world.

Inland, rocky hills go, giving way to mountains, behind which huge wastelands stretch. There is no greenery we are accustomed to, but lichen spots play with paints on the stones, and the damp places are covered with a soft carpet of moss, over which fragile bushes of some plants rise. The day is warm in summer, even hot, but you and I will have to walk in special spacesuits and breathe through an oxygen mask - the ozone layer has not yet formed, and there is too little oxygen in the atmosphere (about 10%) and three times more carbon dioxide than today.

Low tide begins, and not all sea inhabitants keep up with the outgoing waters. Here, on the bare bottom, among the brown-green lumps of algae, brachiopod shells, sea stars and puddles of water, strange creatures slowly crawl. Covered with a segmented shell, they look like giant wood lice. Faceted eyes stand out on the powerful head shield of the carapace, long antennae feel the surface in front of them. As we approach, trilobites try to hide in puddles, and some curl up into a ball. This behavior can save you from a predator, but we can easily catch several specimens, and now is the time to take a closer look.

Armor and legs

Trilobites are arthropods, representatives of the same type as spiders, centipedes, crabs, beetles and butterflies.

The general plan of the structure of trilobites is the same, despite the difference in size and lifestyle. The body is divided into three parts both lengthwise and across. In the transverse plan, these are: head (cephalon), body (thorax) and tail (pygidium). In the longitudinal direction - the central axial lobe (rachis), and two pleural lobes / lobes to the right and left of it. The head shield hides the most important organs - the brain and stomach. The rest of the body segments have the same structure. Through each segment there is a nerve cord with ganglia, an intestine and a long multi-chamber vessel - the heart.

Like all arthropods, the body of the trilobite is covered with a chitinous shell that acts as an exoskeleton. Connective tissue, muscles and internal organs are attached to the shell from the inside. The carapace is not a solid monolithic structure, it consists of many segments, which provides good mobility to the animal. Its thickness is from 1 mm or more in large species. High strength is achieved in two ways: due to the mineralization of chitin with calcium salts and design features. Various ridges, spikes and other growths create additional stiffening ribs that strengthen the trilobite's armor.

The trilobites we caught have a dark, uniform gray-green color, but there are individuals with a reddish-brown shell and spots that look like camouflage.
One of the interesting features of the trilobite is the ability to curl up into a ball in times of danger. Our specimens now look like curled overgrown wood lice. They can stay in this state for a long time, but if you leave them alone, they slowly unfold.

If the trilobite is turned over, we will see many wiggling articulated legs. Since limbs are rarely fossilized, we now have a unique opportunity to study them live. At first glance, it seems that they are the same, but they are not. The very first pair of limbs changed and became antennae - with their help, the trilobite probes and sniffs objects. Under the head shield are four pairs of strong legs that grab and grind food. The limbs on the abdomen and tail are divided into two branches. The main one is the walking leg itself. And a special bristly plate departs from its base. These are the gills, part of the trilobite's respiratory system. In the posterior part, under the pygidium, these brushes are much larger and more massive, and act as swimming blades.

A strong outer skeleton is a good defense against enemies, but it has a significant drawback. It cannot stretch as the animal grows. Therefore, it is necessary to periodically get rid of the shell, shed it. There are special seams on the trilobite's head shield, along which the old shell was torn. The molting process began with the release of the eyes, and their absence in the fossil is one of the signs that we are dealing with a discarded shell. Here, on the shore of the Silurian Sea, these shells are found in large heaps, covered with a layer of sand and silt. Obviously, for molting, trilobites gathered in one place, as modern crabs do, in order to protect each other from enemies.

Keen gaze

Trilobites are one of the first animals to have complex eyes. Peer into these facets - their stony gaze is mesmerizing even after millions of years. And stone is not a metaphor at all. The trilobite eye consists of many facets (from 70 to 10-15 thousand). Each facet contains two lenses. The lower one consists of chitin, while the upper one is a calcite crystal with an admixture of magnesium. It `s very unusual. This kind of "mineral" lenses in the eyes are only found in two groups of living creatures - shell mollusks-chitons, and in echinoderms, ophiurs. But only in trilobites they are developed to perfection and provide good vision. Their origin is the result of parallel evolution and the characteristics of metabolism in these animals.

Trilobites are masters of biochemical work with calcium carbonate. Analysis of fossilized shells and samples taken from living trilobites show a high degree of mineralization of their chitinous armor, which is also not found in any of the arthropods.
Such a device of the eyes made it possible to clearly see objects at a distance of up to several meters, and many facets formed a three-dimensional focused image of the object. In the fossil record, trilobite eyes remain largely unchanged, including color - in some they may be turquoise, emerald green, or yellow.

Sexual question

Like most modern arthropods, trilobites were bisexual and laid eggs.

To distinguish between a male and a female trilobite, you need to pay attention to the shape of the body and the sculptural elements of the carapace. In males, the body is narrower, but the carapace can be richly decorated with outgrowths. In females, the spines and processes of the shell are smaller, but they have a wide, strong body. But the main external difference will still be the brood bag, a special device on the head shield or on its lower side, into which the eggs are placed.

Trilobite larvae bear little resemblance to their parents - they have no eyes, and their body is hidden under an undivided scutellum. Such larvae swim freely in the water column and are carried over long distances by waves and currents. As the young trilobite grows, it becomes more and more like an adult. Many modern marine arthropods also pass through the planktonic stage of reproduction.

Also, like some crustaceans, trilobites are capable of migrating as adults. Trilobites are known to be able to form chains, as do spiny lobsters, and move in large groups over long distances. What makes them migrate, seasonal or not, remains to be seen.

Habitat

In order to study the way of life of trilobites in their natural environment, we will have to dive to the bottom of the Silurian sea in a mobile laboratory and install surveillance cameras.

Our shallow lagoon is separated from the ocean by a barrier reef. Its builders are stromatoporoids, colonial organisms close to sponges. Together with unicellular algae and corals (rugoses and tabules), they form a complex community in which sea lilies, sea anemones, brachiopods and molluscs inhabit.

Here, between the bushes of corals, we meet Paralejurus, small trilobites with a smooth massive cephalon and large eyes. They are numerous, and slowly crawl from place to place in search of food - mollusks, dead horseshoe crabs, shell fish stuck among sea lilies will become their prey. A couple of similar individuals are enthusiastically gnawing a sponge, trying to extract something edible from it.

In general, trilobites are predators leading a near-bottom lifestyle. The main prey is a variety of worms and other soft-bodied invertebrates. Some species ambush prey crawling past - they burrow into the sand, leaving only eyes on the surface, and with a sharp jerk attack their prey. So, for example, Asaphus kowalewskii, which has eyes on long stalks, hunted in this way, but now, in the Silurian, we do not see anything like it. But at night the camera recorded an amazing scene of tracking down prey by another trilobite - Cheirurus. With the spines of the cephalon extended back and sharp like horns, and two elongated spines on the pygidia, heirurus looks intimidating. Crawling quickly along the bottom, he studies the burrows of polychaete worms. One of them caught his attention and the trilobite hid. About an hour passed before the worm appeared from the hole, and as soon as it got out completely, a rapid dash followed, a cloud of sand and silt was thrown into the water. The worm was caught across the body by the front legs of the trilobite, and after a short struggle was torn into several pieces.

Studying the recordings of cameras and going outside in scuba diving, we made sure that the diversity of trilobites is great even in such a tiny area as a small lagoon. The coastal thickets of algae were inhabited by small trilobites that gnawed at their succulent stems. In depressions where silt and sticky mud accumulated, spiked creatures similar to Dicranurus were found. Long shoots on the shell helped them not to drown in this thick sandy-silty jelly.

Some of the burrows that we initially mistook for burrows of worms turned out to be trilobite burrows with a smooth, flattened body and tiny eyes. Eating detritus and small inhabitants of the bottom, they made their own tunnels and sometimes came to the surface at night. Great luck in every sense was the discovery of the true king of the trilobites - Isotelus. Several large, up to a meter in length, individuals lived at the foot of the reef and spent 24 hours on the bottom of the lagoon in search of prey.

Decline of an era

Having received the necessary information and samples, we go back to our time. Our journey into the Silurian period is over, but the history of the trilobites will continue for another 200 million years.

The flowering during the Silurian period will be followed by a gradual decline in the diversity and number of these amazing animals. Devon, the next era, will bring major changes. Fast fish with powerful jaws, capable of gnawing through the strong shells of arthropods, will enter the scene. Ammonites will appear. Among benthic predators, eurypteroids - crustaceans up to two meters long - will occupy a special place. Marine ecosystems will be redesigned to become more and more complex. Gradually, by the Permian period, almost nothing will remain from the former variety of trilobites. The last of the ancients will disappear at the border of the Permian and Triassic, during the Great Extinction, and their ecological niche will eventually be occupied by isopods - isopods.

Several million years ago, our land was inhabited by outlandish and unknown animals. If you believe the theory of evolution, then 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, stegocephals 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 3 cm.

Who are the 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 still find 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 the dinosaurs, then the Paleozoic - of the trilobites. This is a scientific assumption.

Description of appearance

The features of the body structure of trilobites are based on hypotheses and research by scientists. Finds of the remains help to 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. These creatures ranged in size from 5 mm to 81 cm. On the hard cover of trilobites, there could be thorns or horns.

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 the 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 in trilobites are functions of the motor, chewing and respiratory systems. Undoubtedly, they are no less significant reflexes in the body of prehistoric creatures.

But most notable among the extinct trilobites were the senses. True, in some individuals they were absent. lived in muddy waters or at the very bottom of the ocean. In other subspecies, the senses were located on strong legs. When they buried themselves in the sand, the 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 of mineral calcite. The arthropod had a 360-degree angle of view.

These creatures had small antennae-antennae located on the head. Trilobites lived mainly 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 course of their development, they acquired a tail and 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.

Trilobite nutrition and reproduction

There was more than one kind of these amazing organisms. Some ate algae and silt, others plankton. But there were also predatory individuals on the planet. Despite the absence of jaws, they used tentacles to crush their prey. Findings of food in the stomachs of trilobites served as proof of this hypothesis. 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 found fossils.

Examining the remains, scientists came to the conclusion that the extinct animals were heterosexual. This was confirmed by the discovered hatch bag. 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, molted periodically. 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 remotely resemble trilobites are horseshoe crabs. They also appeared in the Ordovician era. Five species of these creatures inhabit the oceans to this day. Horseshoe crabs are similar to trilobites in several ways: mode of movement, dorsal carapace and Both species are the 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 the usual habitable places of Russia. Most of all, they were found in the Leningrad region and in eastern Siberia (Yakutia). In Yakutia, trilobites are diverse and huge in number. But all of their hard surfaces are either crushed or segmented. 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 whole 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 are very interested in these amazing creatures. This is good news, 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.

From all over the country they write that they are allegedly finding living trilobites. However, these are just shields, which 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 look very much like trilobites. But here convergence is to blame (animals in the process of evolution acquire an image similar to each other).

About 3 cm long.

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    ✪ Trilobites. Evolutionary witnesses (told by paleontologists Elena Naimark and Andrey Ivantsov)

    ✪ Origin and extinction of trilobites

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Discovery history

The Trilobita class was identified by Walch in 1771. Trilobita in translation from Latin "three-lobed" ("three-lobed"), because the body of trilobites consists of three lobes. However, trilobites were first described by Llwyd in 1698 under the name Trinuclei. Then the trilobites were described by Linnaeus in 1745 under the name Entomolithes.

Morphology

Torso and tail

The body splits into a middle, or axial, part (rachis) and lateral parts (pleura), while on the caudal shield, as in the continuation of 3 corresponding parts of the body, an axial lobe and lateral lobes are distinguished. The axial parts of the body and caudal shield in the fossilized state are open from below, since they were covered during life with a thin skin, but the lateral parts have preserved a hard curvature, which is usually distinguished by special lines decorating it.

Limbs

Less often, unknown parts of the skeleton are found in fossilized form: limbs (legs) and tentacles. The limbs of trilobites are multifunctional, that is, they performed several functions at once - motor, respiratory and chewing. The appendages of the abdominal side, recently discovered, consist of: 1) of four pairs of limbs above the head shield on the sides of the oral opening, consisting of 6-7 segments and serving as part of the chewing organs. The end members of the posterior pair were in the form of swimming blades; 2) from paired bifurcated limbs, located both under the trunk and under the tail segments, consisting of a number of segments ending in claws. Above the outer branch, there were also special bifurcated and spirally folded appendages, considered as gills.

Sense organs

Trilobites possessed complex faceted eyes that were planted on stalks in those animals that buried themselves in the mud.

In terms of the structure of the eyes, trilobites radically differed from the absolute majority of modern living organisms - instead of a crystalline lens, they had mineral lenses made of calcite. Among modern organisms, mineral visual lenses are found only in the ophiur and the mollusk chiton ( Acanthopleura granulata), however, in terms of the complexity of the device, their organs of vision cannot be compared with the eyes of trilobites.

Folding

Many trilobites had the ability to fold their bodies like wood lice so that the entire soft body was under the shell. Folding served as protection from larger predators.

Spreading

The number of trilobites is quite large. Even Barrand counted more than 1700 species of them, of which 252 belong to the Cambrian period, in the Silurian period: 866 to the Lower Silurian (now the Ordovician period), 482 to the Upper Silurian epochs (now the Silurian period proper), 105 to the Devonian and only 15 to the Carboniferous period; only 1 species passes into the Permian.

The job of classifying trilobites was difficult for paleontologists. It turned out that one cannot proceed from any one feature, but many features must be taken into account 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, moreover, the ability to coagulate is still poorly developed in them. In the Ordovician, the group Asaphidae... They have a constant number of body segments and equal to 8, well-developed compound eyes, the surface is always smooth; family Phacopidae (English) distributed from the Ordovician to the Devonian. They have a constant number of segments of 13 and the eyes have a peculiar appearance. In the Silurian, groups Proetidae (English), Bronteidae, Calymenidae (English) that pass into the Devonian system; in the Carboniferous system, only representatives of the Proetidae are found.

Especially well-preserved remains of trilobites are found in the Yunnan province in China (Maotianshan shale), in the province of Alberta in Canada (Burgess shale), in the state of New York in the USA, and in the Rhineland-Palatinate in the Federal Republic of Germany ( hunsrück shale).

The remains of trilobites are often found in the area of ​​the Lena Pillars in Yakutia.

About 250 million years ago, average annual temperatures skyrocketed (10-20 ° C higher than now), the water warmed up, the oxygen level in many layers of the water dropped to almost zero, and many ancient organisms simply suffocated.

Pattern: Biophoto

In popular culture

  • Trilobites are shown in many popular science films, for example, in "Walks with Sea Monsters" there is the largest of the trilobites - Isotelus, also trilobites are present in "Walks with the Monsters". The trilobite is featured in the adventure film Journey to the Center of the Earth, as well as in the fantastic Japanese film Godzilla vs. Mechagodzilla III.
  • In the album Rengeteg(2011) Hungarian metal band

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