When did the first flags appear? What is a flag? It is a symbol or sign made of fabric. It can be carried, it can be waved, it can flutter. And it is believed that people who carry or hang out any flag thus show their belonging to a certain

When did the first pirates appear? Piracy, or sea robbery, has existed for several millennia. Even ancient Greek and Roman ships were attacked by sea robbers in the Aegean and Mediterranean seas. The pirates were so powerful that even

When did the first acrobats appear? Man has always loved to have fun. Since the beginning of civilization, acrobats, jugglers, animal trainers and clowns have existed for such entertainment. So we cannot say exactly when the first acrobats appeared. Today is ours

When did the first stoves appear? At the beginning of the 15th century, stoves began to appear, although the hearth was still the main source of heat in the house. The stove was more efficient than the hearth, since it is located inside the room, and warms it both by radiating heat and by moving hot air.

When did the first fire brigades appear? Man has always known that fire can be a friend and helper, but it can also be a great destroyer. Primitive man, however, did not have the problem of fighting fire, as we do, simply because he did not live in houses,

Where and when did the first dictionaries appear? From the beginning of the 2nd millennium BC, scribes in Akkad (one of the oldest centers of Babylonia) began to compile Sumerian-Akkadian dictionaries - the first dictionaries in human history. In these dictionaries, Sumerian cuneiform characters

Where and when did the first concentration camps appear? The first concentration camps appeared in 1900 during the Boer War (1899–1902) in South Africa. The war got out of the control of the British, the Boers (Afrikaners) gradually switched to partisan methods

When did the first pirates appear? Piracy, or sea robbery, has existed for several millennia. Even ancient Greek and Roman ships were attacked by sea robbers in the Aegean and Mediterranean seas. The pirates were so powerful that even

). They lived near bodies of water and were closely associated with them, since they reproduced only in water. The development of spaces remote from bodies of water required a significant restructuring of the organization: adaptation to protecting the body from desiccation, breathing atmospheric oxygen, efficient movement on solid substrate, and the ability to reproduce outside of water. These are the main prerequisites for the emergence of a qualitatively different new group of animals - reptiles. These changes were quite complex; for example, it required the development of powerful lungs and a change in the nature of the skin.

Carboniferous period

The remains of the most ancient reptiles are known from the Upper Carboniferous (about 300 million years ago). It is assumed that the separation from amphibian ancestors should have begun, apparently, in the Middle Carboniferous (320 million years), when from anthracosaurs like Diplovertebron, forms became isolated, apparently better adapted to the terrestrial way of life. From such forms a new branch arises - seymuriomorphs ( Seymouriomorpha), the remains of which were found in the Upper Carboniferous - Middle Permian. Some paleontologists classify these animals as amphibians.

Permian period

From the upper Permian deposits of North America, Western Europe, Russia and China know the remains of cotylosaurs ( Cotylosauria). In a number of characteristics they are still very close to stegocephals. Their skull was in the form of a solid bone box with openings only for the eyes, nostrils and parietal organ. cervical region the spine was poorly formed (although there is a structure of the first two vertebrae characteristic of modern reptiles - atlanta And epistrophy), the sacrum had from 2 to 5 vertebrae; the cleithrum, a skin bone characteristic of fish, was preserved in the shoulder girdle; the limbs were short and widely spaced.

The further evolution of reptiles was determined by their variability due to the influence of various living conditions that they encountered during reproduction and settlement. Most groups became more mobile; their skeleton became lighter, but at the same time stronger. Reptiles consumed a more varied diet than amphibians. The technique of its extraction has changed. In this regard, the structure of the limbs, axial skeleton and skull underwent significant changes. For the majority, the limbs became longer, and the pelvis, gaining stability, was attached to two or more sacral vertebrae. The “fishy” bone, the cleithrum, has disappeared from the shoulder girdle. The solid shell of the skull has undergone partial reduction. In connection with the more differentiated muscles of the jaw apparatus, pits and bone bridges separating them appeared in the temporal region of the skull - arches that served to attach a complex system of muscles.

Synapsids

The main ancestral group that gave rise to all the diversity of modern and fossil reptiles were cotylosaurs, but the further development of reptiles followed different paths.

Diapsids

The next group to split off from the cotylosaurs were the diapsids ( Diapsida). Their skull has two temporal cavities, located above and below the postorbital bone. Diapsids at the end of the Paleozoic (Permian) gave an extremely broad adaptive radiation to systematic groups and species, which are found both among extinct forms and among living reptiles. Among diapsids, two main groups emerged: Lepidosauromorphs ( Lepidosauromorpha) and Archosauromorphs ( Archosauromorpha). The most primitive diapsids from the group of Lepidosaurs are the order Eosuchia ( Eosuchia) - were the ancestors of the Beak-headed order, from which only one genus is currently preserved - hatteria.

At the end of the Permian, squamosids separated from primitive diapsids ( Squamata), which became numerous during the Cretaceous period. By the end Cretaceous period Snakes evolved from lizards.

Origin of archosaurs

see also

Write a review of the article "The Origin of Reptiles"

Notes

Literature

• Naumov N. P., Kartashev N. N. Part 2. Reptiles, birds, mammals // Zoology of vertebrates. - M.: graduate School, 1979. - P. 272.

Excerpt characterizing the Origin of Reptiles

Afterwards, I couldn’t come to my senses for a very long time, I became withdrawn, and spent a lot of time alone, which saddened all my family to the core. But, little by little, life took its toll. And, after some time, I slowly began to emerge from that deeply isolated state into which I had plunged myself, and from which it turned out to be very, very difficult... My patient and loving parents tried to help me as best they could. But for all their efforts, they did not know that I was truly no longer alone - that, after all my experiences, an even more unusual and fantastic world suddenly opened up to me than the one in which I had already lived for some time. . A world that surpassed any imaginable fantasy in its beauty, and which (again!) was given to me with its extraordinary essence by my grandfather. This was even more amazing than everything that happened to me before. But for some reason this time I didn’t want to share it with anyone...
Days passed by. In my Everyday life I was an absolutely normal six-year-old child who had my own joys and sorrows, desires and sorrows and such unfulfillable rainbow childhood dreams... I chased pigeons, loved going to the river with my parents, played children's badminton with friends, helped, to the best of my ability , mother and grandmother in the garden, read my favorite books, learned to play the piano. In other words, she lived the most normal, ordinary life of all small children. The only trouble was that by that time I already had two Lives... It was as if I lived in two completely different worlds: the first one was ours ordinary world, in which we all live every day, and the second was my own “hidden” world, in which only my soul lived. It became more and more difficult for me to understand why what was happening to me was not happening to any of my friends?
I began to notice more often that the more I shared my “incredible” stories with someone from my environment, the more often they felt a strange alienation and childish wariness. It hurt and it made me very sad. Children are curious, but they don't like the unknown. They always try as quickly as possible with their childish minds to get to the bottom of what is happening, acting on the principle: “what is it and what do they eat it with?”... And if they cannot understand it, it becomes “alien” for their everyday environment and is very quickly fades into oblivion. This is how I started to become a little “alien”...

Reptiles belong to the group Amniota, which unites them with birds and mammals in the group of true terrestrial vertebrates.

Transformation of the mucous, glandular skin of amphibians into a dry horny cover, protecting the body from drying out, and acquiring the ability to reproduce on landby laying eggs covered with dense shells was a major turning point in the life of terrestrial vertebrates. These changes gave them the opportunity to settle inland, previously inhabited by amphibians only along the shores of freshwater bodies, to new habitats and adapt to very diverse environmental conditions. Before us is a vivid example of a leap in evolution (aromorphosis), which subsequently caused a bright adaptive radiation. Modern turtles, tuataria, scaly reptiles and crocodiles are only the remnants of a once rich fauna. Fossil remains of reptiles show that the reptile fauna in Mesozoic era was extremely diverse, they populated all kinds of stations and dominated the globe.

The most ancient is the order of cotylosaurs (Cotylosauria), which are similar in skull structure to stegocephalians. They are separated in the Lower Carboniferous from embolomeric stegocephali. Currently, the most ancient cotylosaurs of the Seymouriamorpha group, which have such a great similarity with stegocephals that some paleontologists classify them as amphibians, are classified into a special subclass of Batrachosauria, intermediate between amphibians and reptiles.

By the beginning of the Permian period, cotilosaurs became extinct and were replaced by numerous descendants who occupied various stations. Directly from cotylosaurs in the Permian, turtles (Chelonia), which are the most ancient of modern reptiles Therefore, they are combined with cotylosaurs into the common subclass Anapsida. All other subclasses of reptiles are also derived from cotylosaurs as the original group. The central place is occupied by the subclass of archosaurs (Arhosauria), which unites thecodonts, or thecodontia, bird-hipped dinosaurs (Ornitischia), lizard-hipped dinosaurs (Saurischia), crocodiles (Crocodilia) and winged dinosaurs (Pterosauria). To the side of the archosaurs, reptiles branched off from the primary cotylosaurs and returned to an aquatic lifestyle for the second time: fish-like ichthyosaurs (Ichthyosauria) and mesosaurs (Mesosauria), classified as a special subclass of fish-footed animals (Ichthyopterygia), as well as plesiosaurs similar to pinnipeds (Plesiosauria), or lizard-footed ones ( Sauropterygii), and more primitive protorosaurs (Protorosauria). With the exception of crocodiles and turtles, this entire diverse fauna of reptiles became extinct by the beginning of the Tertiary era, replaced by higher vertebrates - birds and mammals.

Modern scaly lizards and snakes (Squamata) and hatteria (Rhynchocephalia), together with fossil eosuchians (Eosuchia), form a subclass of scaly reptiles (Lepidosauria).

Finally, in the Upper Carboniferous, a special group of animal-like lizards (Theromorpha) branched off, which gave rise to the ancestors of mammals. This group includes the orders pelycosauria (Pelycosauria) and therapsids, or beast-like animals (Therapsida), constituting a special subclass of synapsids (Synapsida).

More interesting articles

Origin of reptiles

Origin of reptiles- one of the important issues in the theory of evolution, the process as a result of which the first animals belonging to the class Reptilia appeared.

Permian period

From the Upper Permian deposits of North America, Western Europe, Russia and China, remains of cotylosaurs are known ( Cotylosauria). In a number of characteristics they are still very close to stegocephals. Their skull was in the form of a solid bone box with openings only for the eyes, nostrils and parietal organ, the cervical spine was poorly formed (although there is a structure of the first two vertebrae characteristic of modern reptiles - atlanta And epistrophy), the sacrum had from 2 to 5 vertebrae; the cleithrum, a skin bone characteristic of fish, was preserved in the shoulder girdle; the limbs were short and widely spaced.

The further evolution of reptiles was determined by their variability due to the influence of various living conditions that they encountered during reproduction and settlement. Most groups became more mobile; their skeleton became lighter, but at the same time stronger. Reptiles consumed a more varied diet than amphibians. The technique of its extraction has changed. In this regard, the structure of the limbs, axial skeleton and skull underwent significant changes. For the majority, the limbs became longer, and the pelvis, gaining stability, was attached to two or more sacral vertebrae. The “fishy” bone, the cleithrum, has disappeared from the shoulder girdle. The solid shell of the skull has undergone partial reduction. In connection with the more differentiated muscles of the jaw apparatus, pits and bone bridges separating them appeared in the temporal region of the skull - arches that served to attach a complex system of muscles.

Synapsids

The main ancestral group that gave rise to all the diversity of modern and fossil reptiles were cotylosaurs, but the further development of reptiles followed different paths.

Diapsids

The next group to separate from the cotylosaurs were the Diapsida. Their skull has two temporal cavities, located above and below the postorbital bone. Diapsids at the end of the Paleozoic (Permian) gave an extremely broad adaptive radiation to systematic groups and species, which are found both among extinct forms and among living reptiles. Among diapsids, two main groups emerged: Lepidosauromorpha and Archosauromorpha. The most primitive diapsids from the group of Lepidosaurs are the order Eosuchia ( Eosuchia) - were the ancestors of the Beak-headed order, from which only one genus is currently preserved - hatteria.

At the end of the Permian, squamate (Squamata) separated from the primitive diapsids, becoming numerous in the Cretaceous period. By the end of the Cretaceous period, snakes evolved from lizards.

Origin of archosaurs

see also

• Temporal arches

Notes

Literature

• Naumov N.P., Kartashev N.N. Part 2. Reptiles, birds, mammals // Zoology of vertebrates. - M.: Higher School, 1979. - P. 272.

Wikimedia Foundation. 2010.

Land vertebrates arose in the Devonian. These were armored amphibians, or stegocephali. They were closely associated with bodies of water, since they reproduced only in water and lived near bodies of water, where there was terrestrial vegetation. The development of spaces remote from bodies of water required a significant restructuring of the organization: adaptation to protecting the body from desiccation, breathing atmospheric oxygen, walking on solid substrate, the ability to reproduce outside of water and, of course, improving forms of behavior. These are the main prerequisites for the emergence of a qualitatively different new group of animals. All of the above traits took shape in reptiles.

To this we must add that by the end of the Carboniferous there were strong changes in the natural environment, which led to the emergence of a more diverse climate on the planet, the development of more diverse vegetation, its distribution in areas remote from water bodies, and in this regard to the wide spread of tracheal-breathing arthropods, i.e. .e. possible feeding objects also spread to the watershed areas of the land.

The evolution of reptiles proceeded very quickly and violently. Long before the end of the Permian period of the Paleozoic, they displaced most of the stegocephalians. Having gained the opportunity to exist on land, reptiles in a new environment encountered new and extremely diverse conditions. The versatility of this diversity and the absence of significant competition on land from other animals were the main reasons for the flourishing of reptiles in subsequent times. Mesozoic reptiles are primarily terrestrial animals. Many of them are secondary in one way or another

adapted to life in water. Some have mastered air environment. The adaptive divergence of reptiles was astonishing. The Mesozoic is rightly considered the age of reptiles.

Early reptiles. The oldest reptiles known from the upper Permian deposits of North America, Western Europe, Russia and China. They are called cotylosaurs. In a number of characteristics they are still very close to stegocephalians. Their skull was in the form of a solid bone box with openings only for the eyes, nostrils and parietal organ, the cervical spine was poorly formed, the sacrum had only one vertebra; the cleithrum, a skin bone characteristic of fish, was preserved in the shoulder girdle; the limbs were short and widely spaced.

Cotylosaurs turned out to be very interesting objects, numerous remains of which were found by V.P. Amalitsky in the Permian deposits of Eastern Europe, on the Northern Dvina. Among them are the three-meter herbivorous pareiasaurs (Pareiasaurus).

It is possible that cotylosaurs were descendants of Carboniferous stegocephalians - embolomeres.

In the Middle Permian, cotylosaurs reached their peak. But only a few survived until the end of the Permian, and in the Triassic this group disappeared, giving way to more highly organized and specialized groups of reptiles that developed from various orders of cotylosaurs (Fig. 114).

The further evolution of reptiles was determined by their variability due to the influence of very diverse living conditions that they encountered during reproduction and settlement. Most groups acquired greater mobility; their skeleton became lighter, but at the same time stronger. Reptiles consumed a more varied diet than amphibians. The technique of its extraction has changed. In this regard, the structure of the limbs, axial skeleton and skull underwent significant changes. For the majority, the limbs became longer, and the pelvis, gaining stability, was attached to two or more sacral vertebrae. The cleithrum bone has disappeared in the shoulder girdle. The solid shell of the skull has undergone partial reduction. In connection with the more differentiated muscles of the jaw apparatus, pits and bone bridges separating them appeared in the temporal region of the skull - arches that served to attach a complex system of muscles.

The main groups of reptiles are discussed below, a review of which should show the exceptional diversity of these animals, their adaptive specialization and probable relationship with living groups.

In the formation of the appearance of ancient reptiles and in assessing their subsequent fate, the characteristics of their skull are essential.

Rice. 114. Cotylosaurs (1, 2, 3) and pseudosuchia (4):
1 - pareiasaurus (Upper Permian), skeleton; 2 - pareiasaurus, restoration of the animal; 3 - Seymouria; 4 – pseudosuchia

The primitiveness of stegocephalians ("whole-skull") and early reptiles was expressed in the structure of the skull by the absence of any cavities in it, except for the ocular and olfactory ones. This feature is reflected in the name Anapsida. The temporal region of reptiles of this group was covered with bones. Turtles (now Testudines, or Chelonia) became probable descendants of this trend; they retain a continuous bony cover behind their eye sockets. Similarities with current forms are found in turtles known from the Lower Triassic of the Mesozoic. Their fossil remains are confined to the territory of Germany. The skull, teeth, and shell structure of ancient turtles are extremely similar to modern ones. The ancestor of turtles is considered to be the Permian Eunotosaurus(Eunotosaurus) is a small lizard-like animal with short and very wide ribs that form something like a dorsal shield (Fig. 115). He did not have an abdominal shield. There were teeth. Mesozoic turtles were originally land-dwelling and apparently burrowing animals. Only later did some groups switch to an aquatic lifestyle and, as a result, many of them partially lost their bony and horny shells.

From the Triassic to the present day, turtles have retained the main features of their organization. They survived all the trials that killed off most reptiles, and are just as thriving today as they were in the Mesozoic.

Today's hidden-necked and side-necked ones retain their primary appearance to a greater extent. land turtles Triassic Marine and soft-skinned animals appeared in the late Mesozoic.

All other reptiles, both ancient and modern, acquired one or two temporal cavities in the structure of the skull. They had one, lower, temporal cavity synapsid. One superior temporal cavity is noted in two groups: paranoid and euryansid. And finally, two depressions had diapsid. The evolutionary fate of these groups is different. The first to move away from the ancestral trunk synapsids(Synapsida) - reptiles with lower temporal cavities, bounded by the zygomatic, squamosal and post-orbital bones. Already in the Late Carboniferous, this group of the first amniotes became the most numerous. In the fossil record they are represented by two successively existing orders: pelycosaurs(Pelicosauria) and therapsids(Therapsida). They are also called bestial(Theromorpha). Animal-like animals experienced their heyday long before the first dinosaurs appeared; cotylosaurs were their direct relatives. In particular, pelycosaurs(Pelicosauria) were still very close to cotylosaurs. Their remains were found in North America and in Europe. In appearance they looked like lizards and had small sizes- 1-2 m, had biconcave vertebrae and well-preserved abdominal ribs. However, their teeth sat in the alveoli. In some, teeth differentiation was evident, albeit to a small extent.

In the Middle Permian, pelycosaurs were replaced by more highly organized ones. beast-toothed(Theriodontia). Their teeth were clearly differentiated, and a secondary bony palate appeared. The single occipital condyle split into two. The lower jaw was mainly represented by dentary bone. Position

limbs also changed. The elbow moved back and the knee moved forward, and as a result the limbs began to occupy a position under the body, and not on the sides of it, as in other reptiles. The skeleton appeared to have many features in common with mammals.

Numerous Permian beast-toothed reptiles were very diverse in appearance and lifestyle. Many were predators. Perhaps this was the one found by the expedition of V.P. Amalitsky in the sediments of the Permian period on the Northern Dvina inostranzevia(Inostrancevia alexandrovi, Fig. 116). Others ate a plant-based or mixed diet. These unspecialized species are closest to mammals. Among them it is necessary to point out Cynognathus(Cynognathus), which had many progressive organizational features.

Animal-toothed animals were numerous in the Early Triassic, but with the appearance predatory dinosaurs they disappeared. Interesting materials presented in Table 6 indicate a sharp reduction in the diversity of animal-like animals throughout the Triassic. Animal-like animals are of great interest as the group that gave rise to mammals.

Rice. 116. Animal-toothed:
1 - Inostracevia, Upper Permian (restoration of an animal), 2 - skull of Cynognathus

Table 6

The relationship between the genera of beast-like and sauropsid (lizard-like reptiles) at the end of the Paleozoic - beginning of the Mesozoic
(P Robinson, 1977)

The next group to split off from the anapsid cotylosaurs were diapsid(Diapsida). Their skull has two temporal cavities, located above and below the postorbital bone. Diapsids at the end of the Paleozoic (Permian) gave an extremely broad adaptive radiation to systematic groups and species, which are found both among extinct forms and among living reptiles. Among the diapsids, two main groups (infra-classes) have emerged: infra-class Lepidosauromorphs(Lepidosauromorpha) and infraclass Archosauromorphs(Archosauromorpha).

Paleontologists do not have accurate information to say which of them is older and younger in terms of time of appearance, but their evolutionary fate is different.

Who are lepidosauromorphs? This ancient infraclass unites living hatteria, lizards, snakes, chameleons and their extinct ancestors.

Hatteria, or Sphenodon(Sphenodon punctatus), now living on small islands off the coast of New Zealand, is a descendant of the proto-lizards, or wedge-toothed ones, quite common in the mid-Mesozoic (superorder Prosauria, or Lepidontidae). They are characterized by many wedge-shaped teeth sitting on the jaw bones and on the palate, like amphibians, and amphicoelous vertebrae.

Lizards, snakes and chameleons now make up the wide variety of the order Squamata. Lizards are one of the oldest advanced groups of reptiles, their remains are known from. Upper Permian Scientists have discovered many similarities between lizards and Sphenodon. Their limbs are widely spaced and the body moves, curving the spinal column in waves. Interestingly, among their common morphological similarities is the presence of an intertarsal joint. Snakes appear only in chalk. Chameleons are a specialized group of a later era - the Cenozoic (Paleocene, Miocene).

Now about the fate of archosauromorphs. Archosaurs are considered the most amazing of all reptiles that ever lived on Earth. Among them are crocodiles, pterosaurs, and dinosaurs. Crocodiles are the only archosaurs that have survived to this day.

Crocodiles(Crocodylia) appear at the end of the Triassic. Jurassic crocodiles are significantly different from modern ones in the absence of a true bony palate. Their internal nostrils opened between the palatine bones. The vertebrae were still amphicoelous. Modern crocodiles with a fully developed secondary bony palate and procoelous vertebrae descended from ancient archosaurs - pseudosuchians. They are known from the Cretaceous (about 200 million years ago). Most lived in fresh water bodies, but true marine species are also known among the Jurassic forms.

Winged lizards, or pterosaurs(Pterosauria), represent one of the remarkable examples of specialization Mesozoic reptiles. These were flying animals of a very peculiar structure. Their wings were folds of skin stretched between the sides of the body and the very long fourth finger of the forelimbs. The wide sternum had a well-developed keel, like that of birds; the skull bones fused early; many bones were pneumatic. The jaws extended into a beak bore teeth. The length of the tail and the shape of the wings varied. Some ( Rhamphorhynchus) had long narrow wings and a long tail, they apparently flew in a gliding flight, often gliding. Other's ( pterodactyls) the tail was very short and the wings were wide; their flight was more often rowing (Fig. 117). Judging by the fact that the remains of pterosaurs were found in the sediments of salt water bodies, these were inhabitants of the coasts. They ate

fish and behavior, apparently, were close to gulls and terns. The sizes varied from a few centimeters to a meter or more.

The largest among flying vertebrates belong to the Late Cretaceous winged lizards. These are pteranodons. Their estimated wingspan is 7-12 m, body weight is about 65 kg. They are found on all continents except Antarctica.

Paleontologists suggest a gradual decline in the evolution of this group, which coincided with the appearance of birds.

Dinosaurs(Dinosauria) are known in the fossil record from the mid-Triassic. They are the largest and most diverse group of reptiles ever to live on land. Among the dinosaurs there were small animals, with a body length of less than a meter, and giants up to almost 30 m long. Some of them walked only on their hind legs, others - on all four. The general appearance was also very diverse, but in all of them the head was small relative to the body, and the spinal cord in the sacral region formed a local expansion, the volume of which exceeded the volume of the brain (Fig. 118).

At the very beginning of their formation, dinosaurs were divided into two branches, the development of which proceeded in parallel. Characteristic feature their structure was the pelvic girdle, which is why these groups are called lizard and ornithischian.

Lizard-pelvic(Saurischia) were originally relatively small predatory animals that moved in leaps only on their hind legs, while the front legs served for grasping food. The long tail also served for support. Subsequently, large herbivorous forms appeared that walked on all four legs. These included the largest vertebrates that ever lived on land: brontosaurus had a body length of about 20 m, diplodocus- up to 26 m. Most of the giant lizards were apparently semi-aquatic animals and fed on lush aquatic vegetation.

Ornithischian(Ornithischia) got their name due to their elongated pelvis, similar to the pelvis of birds. Initially, they moved on only elongated hind legs, but later species had both proportionately developed pairs of limbs and walked on four legs. By the nature of their diet, ornithischians were exclusively herbivorous animals. Among them - iguanodon, walking on its hind legs and reaching a height of 9 m. Triceratops in appearance it was very similar to a rhinoceros, usually possessing a small horn at the end of its muzzle and two long horns above the eyes. Its length reached 8 m. Stegosaurus was distinguished by a disproportionately small head and two rows of high bone plates located on the back. Its body length was about 5 m.

Rice. 118. Dinosaurs:
1 - iguanodon; 2 - brontosaurus; 3 - diplodocus; 4 - triceratops; 5 - stegosaurus; 6 – ceratosaurus

Dinosaurs were distributed almost everywhere to the globe and lived in extremely diverse conditions. They inhabited deserts, forests, and swamps. Some led a semi-aquatic lifestyle. There is no doubt that in the Mesozoic this group of reptiles was dominant on land. Dinosaurs reached their greatest prosperity during the Cretaceous, and by the end of this period they became extinct.

Finally, it is necessary to recall another group of reptiles in whose skull there was only one superior temporal cavity. This was typical for parapsids and euryapsids. It has been suggested that they evolved from diapsids by losing the lower cavity. In the fossil record they were represented by two groups: ichthyosaurs(Ichthyosauria) and plesiosaurs(Plesiosauria). Throughout the Mesozoic, from the Early Triassic to the Cretaceous, they dominated marine biocenoses. As noted by R. Carroll (1993), reptiles became secondary aquatic whenever life in water turned out to be more advantageous in terms of the availability of food sources and a small number of predators.

Ichthyosaurs(Ichthyosauria) occupied in the Mesozoic the same place that cetaceans now occupy. They swam, bending their body in waves, especially its tail part, their fins served for control. Their convergent resemblance to dolphins is striking: a spindle-shaped body, an elongated snout and a large two-lobed fin (Fig. 119). Their paired limbs turned into flippers, while the hind limbs and pelvis were underdeveloped. The phalanges of the fingers were elongated, and the number of fingers in some reached 8. The skin was bare. Body sizes varied from 1 to 14 m. Ichthyosaurs lived only in water and ate fish, partly invertebrates. It was established that they were viviparous. Ichthyosaurs appeared in the Triassic and went extinct at the end of the Cretaceous.

Plesiosaurs(Plesiosauria) had other than ichthyosaurs, adaptive features in connection with life at sea: a wide and flat body with a relatively underdeveloped tail. Powerful flippers served as swimming tools. Unlike ichthyosaurs,

They had a well-developed neck carrying a small head. Their appearance resembled pinnipeds. Body sizes range from 50 cm to 15 m. The lifestyle was also different. In any case, some species inhabited coastal waters. They ate fish and shellfish. Having appeared at the beginning of the Triassic, plesiosaurs, like ichthyosaurs, became extinct at the end of the Cretaceous period.

From the above brief overview reptile phylogeny shows that the vast majority of large systematic groups(orders) became extinct before the beginning Cenozoic era and modern reptiles are but miserable remnants of the richest Mesozoic reptile fauna. The reason for this grandiose phenomenon is understandable only in the most general outline. Most Mesozoic reptiles were extremely specialized animals. The success of their existence depended on the presence of very peculiar living conditions. One must think that one-sided deep specialization was one of the prerequisites for their disappearance.

It has been established that although the extinction of individual groups of reptiles occurred throughout the Mesozoic, this became apparent at the end of the Cretaceous period. At this time, in a relatively short period of time, most Mesozoic reptiles became extinct. If it is fair to call the Mesozoic the age of reptiles, then it is no less justified to call the end of this era the age of the great extinction. It should be taken into account that significant changes in climate and landscapes occurred during the Cretaceous. This coincided with significant redistributions of land and sea and movements earth's crust, which led to enormous mountain-building phenomena, known in geology as the Alpine stage of mountain building. It is believed that at this time a large cosmic body passed near the Earth. Violations of the existing living conditions in this regard were very significant. However, they consist not only of changes physical condition Earth and other conditions inanimate nature. In the middle of the Cretaceous period, the Mesozoic flora of conifers, cycads and other plants was replaced by representatives of a new type of flora, namely angiosperms. Genetic changes in the nature of the reptiles themselves cannot be ruled out. Naturally, all this could not but affect the success of the existence of all animals and specialized ones in the first place.

Finally, we must take into account that by the end of the Mesozoic, incomparably more highly organized birds and mammals, which played important role in the struggle for existence between groups of land animals.

Figure 120 gives general scheme phylogeny of reptiles.