When did reptiles appear? Ancient reptiles: origin and extinction

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 fauna of reptiles in the Mesozoic era was extremely diverse, they inhabited 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 stegocephals. 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. Turtles (Chelonia), which are the most ancient of modern reptiles, are taken directly from cotylosaurs in the Permian, so they are combined with cotylosaurs into the common subclass of anapsids (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).

General characteristics of ancient reptiles

Archaic reptiles are the second stage in the ontogenesis of the animal world after amphibians. Ancient reptiles are pioneers among vertebrates that are adapted to life on land.

A common feature of ancient reptiles is the skin of the body, covered dense layer horny formations. Such “protection” made it possible for animals not to be afraid of the scorching rays of the sun and to freely settle over the entire surface of the Earth.

The apogee of the development of ancient reptiles occurs in the Mesozoic era. Archaic dinosaurs are the largest vertebrates living on our planet. Over time, they adapted to fly and swim underwater. In a word, animals reigned supreme in all earthly elements.

The history of ancient reptiles

The cause of the emergence of archaic lizards was a change in climatic conditions. Due to the cooling and drying out of many reservoirs, amphibians were forced to move out of their usual aquatic habitat onto land. As a result of evolution, ancient reptiles appeared as a more advanced link of lower vertebrates.

Climate change has caused major mountain-building processes. Ancient amphibians had thin skin without a protective covering and were underdeveloped internal organs, imperfect lungs. The creatures reproduced primarily by spawning. This method of procreation could not be carried out on land due to the fragility of the future offspring. The lizards laid eggs that had a hard shell and could withstand changing climatic conditions.

The ability to adapt to any habitat led to the emergence of various species of ancient reptiles. The most famous of them:

terrestrial animals (dinosaurs, theriodont lizards, tyrannosaurs, brontosaurs);
swimming fish lizards (ichthyosaurs and plesiosaurs);
flying (pterosaurs).

Types of ancient lizards

Depending on their habitat and method of feeding, archaic reptiles are divided into the following types:

Flying dinosaurs - pterodactyls, rhamphorhynchus, etc. The largest gliding lizard was the pteranodon, whose wingspan reached 16 meters. The rather fragile body deftly moved through the air even in weak winds thanks to a natural rudder - a bone ridge on the back of the head.
Aquatic reptiles - ichthyosaur, mesosaur, plesiosaur. The food of lizard fish was cephalopods, fish and other sea creatures. The body length of aquatic reptiles ranged from 2 to 12 meters.

Herbivorous chordates.
Carnivorous dinosaurs.
Animal-toothed lizards are reptiles whose teeth were not the same, but were divided into fangs, incisors, and molars. The most famous theriodonts are pterosaurs, dinosaurs, etc.

Herbivores

Many ancient reptiles were herbivores - sauropods. Climatic conditions contributed to the development of plants suitable for food by lizards.

The lizards that ate grass included:

Brontosaurus.
Diplodocus.
Iguanodon.
Stegosaurus
Apatosaurus and others.

The teeth of the found remains of reptiles were not developed enough to eat carnal food. The structure of the skeleton indicates the adaptation of archaic animals to pluck leaves located on the crown tall trees: Almost all herbivorous lizards had a long neck and a rather small head. The body of “vegetarians,” on the contrary, was huge and sometimes reached 24 meters in length (for example, a brachiosaurus). Herbivores moved exclusively on four strong legs, and for reliability they also relied on a powerful tail.

Lizard predators

The most ancient reptile predators, unlike their herbivorous relatives, were relatively small in size. The largest representative of archaic carnivores is the tyrannosaurus, whose body reached 10 meters in length. Predators had strong, large teeth and a rather terrifying appearance. Reptile carnivores include:

Tyrannosaurus
Ornithosuchus.
Euparkeria.
Ichthyosaur.

Reasons for the extinction of ancient reptiles

Having adapted to the conditions of the Mesozoic, dinosaurs inhabited almost all habitats. Over time, the climate on Earth began to become harsher. The gradual cooling did not contribute to the comfort of heat-loving animals. As a result, the Mesozoic era became a period of prosperity and disappearance of archaic dinosaurs.

Another reason for the extinction of ancient reptiles is considered to be the spread large quantity plants that are not suitable for dinosaur food. The poisonous grass killed many species of lizards, most of which were herbivores.

The natural struggle for survival did not contribute to the further development of ancient vertebrates. The place of reptiles began to be taken by stronger animals - mammals and birds, warm-blooded and with higher brain development.

The first vertebrates appeared on land in the Devonian. These were stegocephalians, or shell-headed amphibians, the closest relatives of lobe-finned fish. Like the latter, they spent a significant part of their time in bodies of water. However, during periodically recurring droughts, they could crawl out of drying up reservoirs and spend some time on land in search of more favorable conditions.

Origin of reptiles . The ability to remain on land for longer and longer periods of time was determined by the favorable conditions of the subsequent Carboniferous period: the climate was humid, warm and even over most of what was apparently a single continent. But already at the end of the Carboniferous period, the conditions of existence on land changed. Enormous mountain-building processes and movements of land areas relative to the Earth's poles caused changes in climate and vegetation. In many areas of the Earth, the climate has become arid and continental. Tree rings on tree trunks indicate differences in living conditions between seasons. The winters were apparently cold. The lush vegetation of horsetails and ferns associated with lakes and swamps has disappeared. Vast desert spaces appeared. Relatively dry-loving vegetation of conifers and cycads became increasingly dominant.

Living conditions for stegocephals became unfavorable. The dryness of the air made it difficult for them to remain on the surface of the earth for a long time, since their pulmonary respiration was imperfect, and their bare skin could not prevent the body from drying out. At the same time, the desert landscape in many areas did not provide opportunities for the reproduction of stegocephals, which laid their eggs in water. Most stegocephalians became extinct before the Permian period. But at the same time, these environmental conditions caused the appearance of a number of new adaptive characteristics in the most land-dwelling of them.

The decisive adaptations that made it possible to live entirely on land were:

progressive development of the central nervous system, providing more advanced adaptive behavior of animals;
keratinization of the upper layer of the epidermis, and then the appearance of horny scales, which protected the body from drying out;
an increase in the amount of yolk in the egg and the appearance during its development of a number of membranes that protect the embryo from desiccation and at the same time provide the possibility of gas exchange.

Animals were given the opportunity to live and reproduce on land. Naturally, other features of the body appeared at the same time. The limbs became stronger, the skeleton became more durable. The lungs have become more complex, now becoming the only respiratory organ.

Evolution of reptiles

Evolution of reptiles It was going very fast and stormy. Long before the end of the Permian period, they displaced most of the stegocephalians. Having gained the opportunity to exist on land, reptiles in a new environment were faced with new and extremely diverse conditions. The impact of such diverse living conditions and the lack of significant competition on land from other animals served as the main reason that led to the extremely rapid flourishing of reptiles in subsequent times. They were given the opportunity and at the same time were forced to adapt to the most different conditions terrestrial environment. Subsequently, many of them again, to one degree or another, adapted to life in water. Some became air animals. The adaptive divergence of reptiles was astonishing. The Mesozoic is rightly considered the age of reptiles.

Primary reptiles

Cotylosaurs - ancient reptiles, known from the upper Carboniferous deposits.

In a number of characteristics they are still very close to stegocephalians. Thus, many had only one sacral vertebra; The cervical region was poorly developed; in the shoulder girdle there was a cleithrum - a skin bone characteristic of fish. The skull was in the form of a solid bone box with openings only for the eyes, nostrils and parietal organ (hence the name of this group - whole-skull). The limbs were short and not specialized.

Among the generally few cotylosaurs, the most primitive will be Seymouria, found in the Permian deposits of North America, and forms close to it, found on the Northern Dvina, also in the Permian deposits. These were small animals, no more than 0.5 m in size. Large sizes reached the pareiasaurus (Pareiasaurus), numerous remains of which were found by V.P. Amalitskim on the Northern Dvina. Their sizes reached 3 m. Most cotylosaurs were herbivores, some fed on mollusks.

Cotylosaurs reached their peak in the Middle Permian. 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.

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 more durable. Reptiles used an increasingly varied diet. The technique of its extraction has changed. In this regard, the structure of the limbs, axial skeleton and skull underwent significant changes. In most, the limbs became longer, the pelvis 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.

Protolizards (Prosauria) are one of the most primitive groups of reptiles, whose skull had two zygomatic arches. The teeth, like those of amphibians, sat not only on the jaw bones, but also on the palate. The vertebrae were amphicoelous, like those of fish and lower amphibians. In appearance they resemble large lizards. The most ancient representatives are known from Permian deposits. In the Triassic, representatives of the proboscis (Rhynchocephalia) appear, one of the species of which is the hatteria ( Sphenodon punctatus) - preserved to this day in New Zealand.

Pseudosuchia probably originated from the same root as the proto-lizards. They first appear at the beginning of the Triassic. In general appearance and size they were partly similar to lizards. The peculiar features of the organization were that the teeth sat in deep cells; the hind limbs were much more developed than the forelimbs, and for the majority they were the only ones used for walking. In this regard, the pelvis and lower parts of the skeleton of the hind limbs were lengthened. Many apparently led an arboreal lifestyle. Such, for example, are ornithosuchus.

Pseudosuchians are undoubtedly close to crocodiles, pterosaurs and dinosaurs, for the development of which they apparently served as the initial group. Finally, there is reason to believe that pseudosuchia gave rise to the ancestors of birds.

Crocodiles (Crocodilia) appear at the end of the Triassic. Jurassic crocodiles are significantly different from modern ones in the absence of a true bony palate, and their internal nostrils opened between the palatine bones. The vertebrae were still amphicoelous. During the Cretaceous period, modern crocodiles existed with a fully developed secondary bony palate and produral vertebrae. Most lived in fresh water bodies, but true marine species are also known among the Jurassic forms.

Winged lizards (Pterosauria) represent one of the remarkable examples of specialization Mesozoic reptiles. These were flying animals of a very peculiar structure. The instrument of flight was the wings, which were a fold 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 in birds, the bones of the skull fused early, and many bones were pneumatic. In some species, the jaws extended into a beak had 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. Others (pterodactyls) had a very short tail and wide wings; Their flight was often rowing. 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 were apparently close in behavior to gulls and terns. The sizes varied from a few centimeters to a meter or more. Pterosaurs reached their greatest prosperity in the Jurassic. Selected species are also known from Cretaceous deposits.

Dinosaurs (Dinosauria) are the next, last branch of pseudosuchians, the species of which lived from the beginning of the Triassic to the end of the Cretaceous. This is the most numerous and diverse group of reptiles. Among the dinosaurs there were small animals with a body length of less than a meter and giants up to almost 30 m in length. Some of them walked only on their hind legs, others on all four legs. The general appearance of the body was also very diverse, but all of them had a relatively small head, and the spinal cord in the sacral region formed a local expansion, the volume of which exceeded the volume of the brain.

At the very beginning of their separation from pseudosuchians, dinosaurs were divided into two branches, the development of which proceeded in parallel. A characteristic feature of them was the structural features of the pelvic girdle, and therefore these groups are called ornithischian and lizard-pelvic.

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

Ornithischians get their name due to their elongated pelvis, similar to the pelvis of birds. Initially, they walked on only elongated hind legs, but later species had both pairs of limbs proportionately developed and walked on four legs. By the nature of their diet, ornithischians were exclusively herbivorous animals. Among them, we mention the iguanodons, which walked only on their hind legs and reached 9 m in height. Their skin was without a bone shell. Triceratops was very similar in appearance to a rhinoceros, usually possessing a small horn at the end of its snout and two long horns above the eyes. Its length reached 8 m. Stegosaurus was characterized by a disproportionately small head and two rows of high bone plates located on its back. Its length was about 5 m.

Dinosaurs were distributed almost everywhere to the globe and lived in extremely diverse living conditions. They inhabited deserts, forests, and swamps. Some (for example, trachodonts) led a semi-aquatic lifestyle. There is no doubt that in the Mesozoic dinosaurs were the dominant group of reptiles on land. They appeared in the Triassic and reached their greatest prosperity in the Cretaceous. By the end of this period, dinosaurs became extinct.

Scaly (Squamata). The history of this currently largest detachment is the least clear.

Lizards apparently appeared in the Upper Jurassic, but only in the Cretaceous period is relative diversity of this suborder observed. Snakes evolved later than all other reptiles. They appeared only towards the end of the Cretaceous, undoubtedly as the side trunk of lizards. The real flourishing of squamates came only in Tertiary times, when most groups of reptiles became extinct.

Turtles (Chelonia) represent one of the oldest reptiles, apparently descended directly from cotylosaurs. Their ancestor is considered to be the Permian Eunotosaurus. This is a small lizard-like animal with short and very wide ribs that form a kind of dorsal shield. They did not have an abdominal shield. There were teeth. In the Triassic, real turtles with developed real shells appeared (for example, Triassochelys).

However, their head and limbs could not yet be completely retracted into the shell. A horny sheath was developed on the jaws, but at the same time there were teeth on the palate. Mesozoic turtles were originally land-dwelling and apparently burrowing animals. Only later did some groups switch to an aquatic lifestyle and, as a result, partially lost their bony and horny shells.

Throughout the entire period from the Triassic to the present day, turtles have retained all the main features of their organization. They have survived all the challenges that killed off most reptiles and are thriving today as much as they were in the Mesozoic.

Ichthyosaurs (Ichthyosauria) are reptiles that are most fully adapted to life in water. In the nature of the Mesozoic, they occupied the same place that cetaceans now occupy. Their convergent resemblance to dolphins is striking. They had a spindle-shaped body, an elongated snout and a large two-lobed fin. The paired limbs were 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. The appearance of ichthyosaurs dates back to the Triassic. They became extinct during the Cretaceous period. Genetic relationships with other reptiles have not been clarified.

Plesiosaurs (Plesiosauria) - the second group of Mesozoic marine reptiles with other adaptive features organizations. Ichthyosaurs swam, bending their body and especially its tail in waves; their fins served for control. Plesiosaurs had a wide and flat body with a relatively underdeveloped tail. Powerful flippers served as swimming tools. Unlike ichthyosaurs, they had a well-developed neck supporting a small head. Body sizes range from 50 cm to 15 m. Apparently, the lifestyle was also different. In any case, some species inhabited coastal waters. They ate fish and shellfish.

Plesiosaurs appeared at the beginning of the Triassic. At the end of the Cretaceous period they became extinct.

The beast-like animals (Theromorpha) are of great interest as the group that gave rise to mammals.

Animal-like animals are one of the most ancient groups of reptiles. Its appearance dates back to the end of the Carboniferous, and in the Permian they were already numerous and diverse. Animal-like animals experienced their heyday long before the first dinosaurs appeared, and cotylosaurs were their direct relatives. Primitive animal-like animals, allocated to the order Pelycosauria (Pelycosauria), were still very close to cotylosaurs. Thus, they had biconcave vertebrae and well-preserved abdominal ribs. However, their teeth sat in the alveoli, and in the temporal region of the skull there was a lateral depression not characteristic of any other group of reptiles. In appearance they looked like lizards and had small sizes- 1-2 m. In some, differentiation of teeth was evident, albeit to a small extent (for example, in Sphenacodon).

In the Middle Permian, pelycosaurs were replaced by more highly organized animals (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. The position of the limbs also changed. The elbow moved back and the knee forward, and as a result the limbs began to occupy a position under the body, and not on its sides, as in other reptiles. The skeleton appeared to have many features in common with mammals.

Among the numerous Perm animal-like animals there were reptiles that were very diverse in appearance and lifestyle. Many were predators. Such, for example, is Inostrancevia aiexandrovi, found by the expedition of V.P. Amalitsky in Permian deposits on the Northern Dvina. Others ate a plant-based or mixed diet. These unspecialized species are closest to mammals. Among them, we must point out Cynognathus, which had many progressive organizational features.

Animal-toothed animals were numerous even in the Triassic, but with the appearance predatory dinosaurs they disappeared.

From the above overview of reptile phylogeny, it is clear that the vast majority of large systematic groups their (orders) became extinct before the beginning Cenozoic era, And modern reptiles represent only the pitiful remains of the Mesozoic fauna.

The reason for this grandiose phenomenon is understandable only in the most general terms. It is noteworthy that most Mesozoic reptiles were extremely specialized animals. The success of their existence depended on the presence of very unique, narrowly defined living conditions. One must think that one-sided specialization was one of the prerequisites for the disappearance of most Mesozoic reptiles.

It was established that, although the extinction of individual groups of reptiles was observed throughout the Mesozoic and the end of the Paleozoic, it was especially pronounced at the end of the Mesozoic, precisely at the end of the Cretaceous period. At this time, in a relatively short period of time, the vast majority of Mesozoic reptiles became extinct. If it is true 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. Along with the above, it has been established that particularly significant changes in climate and landscapes were observed during the Cretaceous. This was associated 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”. Violations of the existing living conditions in this regard were very significant. They consist not only in changes in climate, orography of the Earth and other conditions of dead nature. It is enough to point out that in the middle of the Cretaceous period, the Mesozoic flora of conifers, cycads and others was replaced by plants of a new type, namely angiosperms. Naturally, all this could not but affect the success of the existence of all animals, and the one-sidedly 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 a very important role in the struggle for existence between groups of terrestrial animals, began to develop more and more.

Origin of reptiles

The remains of the most ancient reptiles are known from the Upper Carboniferous period (Upper Carboniferous; age approximately 300 million years). However, their separation from amphibian ancestors should have begun earlier, apparently in the Middle Carboniferous (320 million years), when forms, apparently more terrestrial, separated from primitive embolomeric stegocephalians - anthracosaurs similar to Diplovertebron. Like their ancestors, they were still associated with wet biotopes and bodies of water, fed on small aquatic and terrestrial invertebrates, but had greater mobility and a somewhat larger brain; perhaps they have already begun to become keratinized.

In the Middle Carboniferous, a new branch arose from similar forms - Seymourioraorpha. Their remains were found in the Upper Carboniferous - Lower Permian. They occupy a transitional position between amphibians and reptiles, having undoubted reptilian features; some paleontologists classify them as amphibians. The structure of their vertebrae ensured greater flexibility and at the same time strength of the spine; there has been a transformation of the first two cervical vertebrae into the atlas and epistropheus. For terrestrial animals, this created important advantages in orientation, hunting for moving prey, and protection from enemies. The skeleton of the limbs and their girdles was completely ossified; there were long bony ribs, but not yet closed into the chest. The limbs, stronger than those of stegocephals, lifted the body above the ground. The skull had an occipital condyle; Some forms retained gill arches. Seymuria, Kotlassia (found on the Northern Dvina), like other seymuriomorphs, were still associated with reservoirs; it is believed that they may still have had aquatic larvae.

When did the inherent pattern of reproduction and development of the egg in amniotes take shape? air environment, It's not clear yet. It can be assumed that this happened in the Carboniferous during the formation of cotylosaurs - Cotylosauria. Among them were small lizard-like forms that apparently fed on various invertebrates, and large (up to 3 m long) massive herbivorous pareiasaurs such as the Severodvinsk scutosaurus. Some cotylosaurs led a semi-aquatic lifestyle, inhabiting humid biotopes, while others, apparently, became true terrestrial inhabitants.

Warm and humid climate Carboniferous favored amphibians. At the end of the Carboniferous - beginning of the Permian, intense mountain building (uplift of the mountains of the Urals, Carpathians, Caucasus, Asia and America - the Hercynian cycle) was accompanied by dismemberment of the relief, increased zonal contrasts (cooling in high latitudes), a decrease in the area of wet biotopes and an increase in the proportion of dry biotopes. This contributed to the emergence of terrestrial vertebrates.

The main ancestral group that gave rise to all the diversity of fossils and modern reptiles were the above-mentioned cotylosaurs. Having reached their peak in the Permian, they, however, became extinct by the middle of the Triassic, apparently under the influence of competitors - various progressive groups of reptiles that separated from them. In the Permian, turtles separated from cotylosaurs - Chelonia - their only direct descendants that have survived to this day. In the first turtles, such as the Permian Eunotosaurus, the sharply expanded ribs do not yet form a continuous dorsal shell. Seymuriomorphs, cotylosaurs and turtles are grouped into the subclass Anapsida.

Apparently, in the Upper Carboniferous, two subclasses of reptiles evolved from cotylosaurs, which again switched to an aquatic lifestyle:

Order of mesosaurs.

Order of ichthyosaurs.

The subclass of synaptosaurs, Synaptosauria, includes two orders. order protorosaurs - Protorosauria order sauropterygia - Sauropterygia These include nothosaurs and plesiosaurs.

Proganosaurs and synaptosaurs went extinct without leaving descendants.

In the Permian, a large branch of diapsid reptiles separated from cotylosaurs, in the skull of which two temporal pits formed; this group subsequently split into two subclasses: the lepidosaur subclass and the archosaur subclass.

The most primitive diapsids are the order of eosuchians - Eosuchia of the subclass Lepidosauria - small (up to 0.5 m), lizard-like reptiles; had amphicoelous vertebrae and small teeth on the jaws and palatine bones; went extinct at the beginning of the Triassic. In the Permian, beak-headed animals, Rhynchocephalia, separated from some eosuchians, distinguished by large temporal pits, a small beak at the end of the upper jaws and hook-shaped processes on the ribs. Beakheads became extinct at the end of the Jurassic, but one species - New Zealand tuateria- has survived to this day.

At the end of the Permian, squamate - Squamata (lizards), became numerous and diverse in the Cretaceous, separated from primitive diapsids (possibly directly from eosuchians). At the end of this period, snakes evolved from lizards. The heyday of squamates occurred in the Cenozoic era; they make up the vast majority of living reptiles.

The most diverse in forms and ecological specialization in the Mesozoic era was the subclass of archosaurs Archosauria. Archosaurs inhabited land, bodies of water, and conquered the air. The original group of archosaurs were thecodonts - Thecodontia (or pseudosuchians), which separated from the eosuchians, apparently in the Upper Permian and reached their peak in the Triassic. They looked like lizards ranging from 15 cm to 3-5 m in length, most led a terrestrial lifestyle; the hind limbs were usually longer than the forelimbs. Some of the thecodonts (ornithosuchians) probably climbed branches and led an arboreal lifestyle; Apparently, the class of birds later evolved from them. Another part of the thecodonts switched to a semi-aquatic lifestyle; From them, at the end of the Triassic, crocodiles arose - Crocodilia, which formed many different forms in the Jurassic - Cretaceous.

In the mid-Triassic, the thecodonts gave rise to flying dinosaurs, or pterosaurs, Pterosauria; Pterosaurs were widespread and numerous during the Jurassic and Cretaceous periods; completely died out, leaving no descendants, by the end of the Cretaceous. The extinction may have been facilitated by competition with the increasingly numerous birds at that time. It should be emphasized that pterosaurs and birds are completely independent branches of evolution, the ancestral forms of which were different families of the thecodont order.

In the Upper Triassic, two more groups separated from the carnivores that moved primarily on the hind limbs of pseudosuchians (thecodonts): saurischian dinosaurs - Saurischia and ornithischian dinosaurs - Ornithischia. Saurischian and ornithischian dinosaurs differed in the details of the structure of the pelvis. Both groups developed in parallel; in the Jurassic and Cretaceous periods they gave an extraordinary variety of species, ranging in size from rabbits to giants weighing 30-50 tons; lived on land and coastal shallow waters. By the end of the Cretaceous period, both groups became extinct, leaving no descendants.

Finally, the last branch of reptiles - the subclass animal-like, or synapsids - Theromorpha or Synapsida, was almost the first to separate from the general trunk of reptiles. They separated from the primitive Carboniferous cotylosaurs, which apparently inhabited wet biotopes and still retained many amphibious features (skin rich in glands, the structure of the limbs, etc.). Synapsids began a special line of reptilian development. Already in the Upper Carboniferous and Permian there arose various forms, united in the order of pelycosaurs - Pelycosauria. They had amphicoelous vertebrae, a skull with a poorly developed one fossa and one occipital condyle, there were teeth on the palatine bones, and there were abdominal ribs. In appearance they resembled lizards, their length did not exceed 1 m; only single species reached 3-4 m in length. Among them were true predators and herbivorous forms; many led a terrestrial lifestyle, but there were semi-aquatic and aquatic forms. By the end of the Permian, pelycosaurs became extinct, but before that the beast-toothed reptiles - therapsids - Therapsida separated from them. The adaptive radiation of the latter occurred in the Upper Permian - Triassic, with continuously increasing competition from progressive reptiles - especially archosaurs. Therapsid sizes varied widely: from a mouse to a large rhinoceros. Among them were herbivores - Moschops - and large predators with powerful fangs - Inostrancevia (skull length 50 cm; Fig. 5), etc. Some small forms had, like rodents, large incisors and, apparently, led a burrowing lifestyle. By the end of the Triassic - the beginning of the Jurassic, diverse and well-armed archosaurs completely replaced the beast-toothed therapsids. But already in the Triassic, some group of small species, probably inhabiting damp, densely overgrown biotopes and capable of digging shelters, gradually acquired the features of a more progressive organization and gave rise to mammals.

Thus, as a result of adaptive radiation, already at the end of the Permian - beginning of the Triassic, a diverse fauna of reptiles (approximately 13-15 orders) emerged, displacing most groups of amphibians. The flourishing of reptiles was ensured by a number of aromorphoses, which affected all organ systems and ensured increased mobility, intensified metabolism, greater resistance to a number of environmental factors (dryness in the first place), some complication of behavior and better survival of offspring. The formation of temporal pits was accompanied by an increase in the mass of the chewing muscles, which, along with other transformations, made it possible to expand the range of food used, especially plant foods. Reptiles not only widely mastered the land, populating a variety of habitats, but returned to the water and rose into the air. Throughout Mesozoic era- for more than 150 million years - they occupied a dominant position in almost all terrestrial and many aquatic biotopes. At the same time, the composition of the fauna changed all the time: ancient groups died out, replaced by more specialized young forms.

By the end of the Cretaceous period, two new classes of warm-blooded vertebrates had already formed - mammals and birds. The specialized groups of large reptiles that survived until this time could not adapt to changing living conditions. In addition, increasing competition with smaller but active birds and mammals played an active role in their extinction. These classes, having acquired warm-bloodedness, steadily high level metabolism and more challenging behavior, increased in number and importance in communities. They quickly and efficiently adapted to life in changing landscapes, quickly mastered new habitats, intensively used new food, and had an increasing competitive effect on more inert reptiles. The modern Cenozoic era began, in which birds and mammals occupied a dominant position, and among the reptiles only relatively small and mobile scaly ones (lizards and snakes), well-protected turtles and a small group of aquatic archosaurs - crocodiles - were preserved.

Fossil reptiles are of exceptional interest, since they belong to numerous groups that once dominated the globe. Ancient groups of this class gave rise not only to modern reptiles, but also to birds and mammals. The oldest reptiles belonging to the order of cotylosaurs, or whole-skulls (Cotylosauria), from the subclass of anapsids, are already known from the upper Carboniferous deposits, but only in the Permian period did they achieve significant development, and in the Triassic they already became extinct. Cotylosaurs were massive animals with thick, five-toed legs and body lengths ranging from several tens of centimeters to several meters. The skull was covered with a solid shell of dermal bones with openings only for the nostrils, eyes and parietal organ. This structure of the skull, as well as many other features, indicate the extreme closeness of cotylosaurs to primitive stegocephalians, which undoubtedly were their ancestors. The most primitive of the so far known anapsids, and therefore of reptiles in general, is the Lower Permian Seymouria. This relatively small (up to 0.5 m in length) reptile had a number of features characteristic of amphibians: the neck was almost not pronounced, the long sharp teeth still retained a primitive structure, there was only one sacral vertebra, and the bones of the skull showed remarkable similarities even in details with the cranial cover of stegocephali. Fossil remains of seymuriomorphic reptiles were found in the area former USSR(Kotlasia and others), made it possible for Soviet paleontologists to identify them systematic position as representatives of a special subclass of batrachosaurs (Batrachosauria), occupying an intermediate position between amphibians and cotylosaurs. Cotylosaurs are a very diverse group. The most major representatives Its members are the clumsy herbivorous pareiasaurs (Pareiasaurus), reaching 2-3 m in length. Later, their skeletons were found in South Africa and here on the Northern Dvina. Cotylosaurs were the original group that gave rise to all other major groups of reptiles. Evolution mainly proceeded along the path of the emergence of more mobile forms: the limbs began to lengthen, at least two vertebrae took part in the formation of the sacrum, the entire skeleton, while maintaining its strength, became lighter, in particular, the initially solid bone shell of the skull began to be reduced by the appearance of temporal pits, which not only lightened the skull, but, most importantly, helped to strengthen the muscles that compress the jaws, since if a hole is formed in the bone plate to which the muscles are attached, the muscle, when contracting, can protrude somewhat into this hole. The reduction of the cranial shell proceeded in two main ways: by the formation of one temporal fossa, limited below by the zygomatic arch, and by the formation of two temporal fossae, resulting in the formation of two zygomatic arches. Thus, all reptiles can be divided into three groups: 1) anapsids - with a solid cranial shell (cotylosaurs and turtles); 2) synapsids - with one zygomatic arch (animal-like, plesiosaurs and, possibly, ichthyosaurs) and 3) diapsids - with two arches (all other reptiles). The first and second groups each contain one subclass, the latter is divided into a number of subclasses and many orders. The anapsid group is the oldest branch of reptiles, which have many common features in their skull structure with fossil stegocephalians, since not only many of their early forms (cotylosaurs), but even some modern ones (some turtles) have a solid cranial shell. Turtles are the only living representatives of this ancient group of reptiles. They apparently separated directly from the cotylosaurs. Already in the Triassic ancient group has completely developed and, thanks to its extreme specialization, has survived to the present day, almost unchanged, although in the process of evolution, some groups of turtles switched several times from a terrestrial lifestyle to an aquatic one, due to which they either almost lost their bony shields or acquired them again. From the group of cotylosaurs, marine fossil reptiles separated - ichthyosaurs and plesiosaurs, which, together with other rarer forms, formed two independent subclasses: Ichthyopterygia and Synaptosauria. Plesiosaurs (Plesiosauria), related to synaptosaurs, were marine reptiles. They had a wide, barrel-shaped, flattened body, two pairs of powerful limbs modified into swimming flippers, a very long neck ending in a small head, and a short tail. The skin was bare. Numerous sharp teeth sat in separate cells. The sizes of these animals varied over a very wide range: some species had only half a meter in length, but there were also giants that reached 15 m. A characteristic feature of their skeleton was the underdevelopment of the dorsal parts of the limb girdles (scapula, ilium) and the exceptional thickness of the abdominal girdles (coracoid) , abdominal process of the scapula, pubic and ischial bones), as well as abdominal ribs. All this indicates an exceptionally strong development of the muscles that move the flippers, which served only for rowing and could not support the body out of the water. Although within the subclass of synaptosaurs the transition from terrestrial to aquatic forms has been restored quite clearly, the origin of the group as a whole is still largely unclear. While plesiosaurs, having adapted to aquatic life, still retained the appearance of terrestrial animals, ichthyosaurs (Ichthyosauria), belonging to ichthyopterygians, acquired similarities with fish and dolphins. The body of ichthyosaurs was spindle-shaped, the neck was not pronounced, the head was elongated, the tail had a large fin, and the limbs were in the form of short flippers, with the hind ones being much smaller than the front ones. The skin was bare, numerous sharp teeth (adapted to feeding on fish) sat in a common groove, there was only one zygomatic arch, but of an extremely unique structure. The sizes varied from 1 to 13 m. The diapsid group includes two subclasses: lepidosaurs and archosaurs. The earliest (Upper Permian) and most primitive group of lepidosaurs is the order Eosuchia. They are still very poorly studied, the best known is lounginia - a small reptile, resembling a lizard in body, with relatively weak limbs that had the usual reptilian structure. Its primitive features are expressed mainly in the structure of the skull; teeth are located both on the jaws and on the palate. The first beaked animals (Rhynchocephalia) have been known since the Early Triassic. Some of them were extremely close to the modern hatteria. Beakheads differ from eosuchians in the presence of a horny beak and in the fact that their teeth are attached to the bone, while the jaw teeth of eosuchians sat in separate cells. According to the last feature, beakheads are even more primitive than eosuchians and, therefore, should have descended from some as yet undiscovered primitive forms of the latter group. Squamata, namely lizards, are known only from the very end of the Jurassic. Mosasauria (Mosasauria) apparently separated from the main trunk of squamate lizards already at the beginning of the Cretaceous. These were sea reptiles that had a long serpentine body and two pairs of limbs modified into flippers. Some representatives of this order reached a length of 15 m. At the end of the Cretaceous they died out without a trace. Somewhat later than the mosasaurs (end of the Cretaceous), a new branch separated from lizards - snakes. In all likelihood, a large progressive branch of archosaurs (Archosauria) originated from Eosuchia - namely pseudosuchia, which subsequently split into three main branches - aquatic (crocodiles), terrestrial (dinosaurs) and airborne (winged lizards). Along with the two typical temporal arches, the most characteristic feature of this group was the tendency to transition to “bipedalism,” that is, movement on only the hind limbs. True, some of the most primitive archosaurs only began to change in this direction, and their descendants took a different path, and representatives of a number of groups returned to moving on four limbs for the second time. But in the latter case past history left a mark on the structure of their pelvis and the hind limbs themselves. Pseudosuchia first appeared only at the beginning of the Triassic. The early forms were small animals, but with relatively long hind legs, which, apparently, served them alone for movement. The teeth, which were present only on the jaws, sat in separate cells, and bone plates were almost always located in several rows along the back. These small forms, typical representatives of which are ornithosuchians, and apparently leading the arboreal life of Scleromochlus, were very numerous and gave rise not only to branches that flourished later - in the Jurassic and Cretaceous, but also to a number of highly specialized groups that became extinct without a trace. in the Triassic. Finally, pseudosuchians, in particular, if not Ornithosuchus itself, then forms close to it, could be the ancestors of birds. Crocodiles (Crocodylia) are very close to some Triassic pseudosuchians, such as Belodon, or Phytosaurus. Starting from the Jurassic, real crocodiles appeared, but the modern type of crocodiles was finally developed only during the Cretaceous period. On this long path of evolution, you can trace step by step how the characteristic feature crocodiles - secondary palate. At first, only horizontal processes appeared on the maxillary and palatine bones, then these palatine processes converged, and even later they were joined by the palatine processes of the pterygoid bones, and simultaneously with this process the nostrils moved forward, and the secondary choanae moved backward. Dinosaurs (Dinosauria) are the most numerous and diverse group of reptiles that have ever lived. These included small forms, the size of a cat and smaller, and giants, reaching almost 30 m in length and 40-50 tons in weight, light and massive, agile and clumsy, predatory and herbivorous, devoid of scales and covered with a bony shell with various outgrowths. Many of them ran galloping on one hind limb, leaning on the tail, while others moved on all four. Dinosaurs' heads were usually relatively small, while the cavity of the cranium was very tiny. But the spinal canal in the sacral area was very wide, which indicates a local expansion of the spinal cord. Dinosaurs were divided into two large groups- lizard and ornithischians, which arose completely independently from pseudosuchians. Their differences lie mainly in the structure of the hind limb girdle. Lizard hippies (Saurischia), family ties which with pseudosuchia there is no doubt, were originally only predatory. Subsequently, although most forms continued to remain carnivorous, some turned into herbivores. The predators, although they reached enormous sizes (up to 10 m in length), had a relatively light build and a powerful skull with sharp teeth. Their forelimbs, which apparently served only for grasping prey, were greatly reduced, and the animal had to move by jumping on its hind limbs and leaning on its tail. A typical representative of such forms is Ceratosaurus. In contrast to predatory herbivorous forms, they moved on both pairs of limbs, which were almost equal in length and ended in five fingers, apparently covered with horny formations like hooves. These included the largest four-legged animals that ever lived on the globe, such as the Brontosaurus, which reached over 20 m in length and probably 30 tons in weight, and Diplodocus. The latter was slimmer and, undoubtedly, much lighter, but it was superior to the Brontosaurus in length, which in one specimen exceeded 26 m; finally, the lumbering Brachiosaurus, about 24 m long, must have weighed about 50 tons. Although hollow bones lightened the weight of these animals, it is still difficult to believe that such giants could move freely on land. Apparently, they led only a semi-terrestrial life and, like modern hippopotamuses, spent most of their time in the water. This is indicated by their very weak teeth, suitable for eating only soft aquatic vegetation, and the fact that, for example, Diplodocus's nostrils and eyes were moved upward, so that the animal could see and breathe with only part of its head out of the water. Ornithischia, which had a girdle of hind limbs extremely similar to a bird's, never reached such enormous sizes. But they were even more diverse. Most of these animals returned to moving on four legs for the second time and usually had a well-developed shell, sometimes complicated by various kinds of outgrowths in the form of horns, spines, etc. All of them remained herbivorous from the very beginning to the end, and the majority retained only their back teeth, while the front of the jaws was apparently covered with a horny beak. Iguanodons, stegosaurs and triceratops can be mentioned as characteristic representatives of various groups of ornithischians. Iguanodons, which reached 5-9 m in height, ran on only their hind legs and were deprived of a shell, but the first finger of their forelimbs was a bone spike that could serve a good tool protection. Stegosaurus had a tiny head, a double row of tall triangular bony plates on its back, and several sharp spines perched on its tail. Triceratops looked like a rhinoceros: at the end of its snout there was a large horn, in addition, a pair of horns rose above the eyes, and along the rear, extended edge of the skull there were numerous pointed processes. Pterodactyls (Pterosauria), like birds and bats, were true flying animals. Their forelimbs were real wings, but of an extremely unique structure: not only the forearm, but also the metacarpal bones fused to each other were greatly elongated, the first three fingers had a normal structure and size, the fifth was absent, while the fourth reached extreme length and between them and a thin flying membrane was stretched along the sides of the body. The jaws were extended, some forms had teeth, others had a toothless beak. Pterodactyls exhibit a number of common features with birds: fused thoracic vertebrae, a large sternum with a keel, a complex sacrum, hollow bones, a sutureless skull, and large eyes. The winged lizards apparently ate fish and probably lived on coastal rocks, since, judging by the structure of their hind limbs, they could not rise from a flat surface. Pterodactyls include quite diverse forms: a relatively primitive group of rhamphorhynchus, which had a long tail, and pterodactyls themselves with a rudimentary tail. The sizes ranged from the size of a sparrow to a giant pteranodon, whose wingspan reached 7 m. The group of synapsids constitutes an independent subclass of reptiles, as a special side branch that separated from the ancient cotylosaurs. They are characterized by strengthening of the jaw apparatus by the formation of a kind of temporal cavity for very powerful jaw muscles and progressive differentiation of the dental system - heterodontism, or heterodonty. This connects them with the highest class of vertebrates - mammals. Animal-like (Theromorpha) is a group whose primitive representatives were still very close to cotylosaurs. Their difference lies mainly in the presence of a zygomatic arch and a lighter build. Animal-like animals appeared at the end of the Carboniferous period, and starting from the Lower Permian they became very numerous and during this entire period, together with cotylosaurs, they were almost the only representatives of their class. Despite all their diversity, all beast-like animals were strictly terrestrial animals, moving exclusively with the help of both pairs of limbs. The most primitive representatives of pelycosaurs (for example, Varanops) were small in size and should have looked like lizards. However, their teeth, although homogeneous, were already sitting in separate cells. The mammals (Therapsida), which replaced the pelycosaurs from the Middle Permian, united extremely diverse animals, many of which were highly specialized. In later forms, the parietal foramen disappeared, the teeth differentiated into incisors, canines and molars, a secondary palate was formed, one condyle was divided into two, the dentary bone increased greatly, while the other bones of the lower jaw decreased. The reasons for the extinction of ancient reptiles are still not entirely clear. The most plausible explanation for this phenomenon is the following. In the process of struggle for existence, individual forms became more and more adapted to certain environmental conditions and became more and more specialized. Such specialization is extremely useful, but only as long as the conditions to which the organism has adapted continue to exist. Once they change, such animals find themselves in worse conditions than the less specialized forms that supplant them in the struggle for existence. In addition, in the struggle for existence, some groups may acquire properties that increase their overall vital activity. In contrast to narrow adaptation, or idioadaptation, this phenomenon is called aromorphosis. For example, warm-bloodedness made it possible for organisms that acquired this property to be less dependent on climate compared to animals with variable body temperature. During the long Mesozoic era, there were only minor changes in landscapes and climate, and therefore reptiles became more and more specialized and flourished. But at the end of this era earth's surface began to undergo such huge mountain-building processes and associated climate change that most reptiles could not survive them and died out without a trace by the end of the Mesozoic, which was called the era of the great extinction. However, it would be a mistake to explain this process solely by physical and geographical reasons. An equally important role was played by the struggle for existence with other animals, namely with birds and mammals, which, thanks to their warm-bloodedness and highly developed brain, turned out to be better adapted to these external phenomena and emerged victorious in the struggle of life.

Literature

1. Vorontsova M. A., Liozner L. D., Markelova I. V., Puhelskaya E. Ch. Triton and axolotl. M., 1952.

2. Gurtovoy N. N., Matveev B. S., Dzerzhinsky F. Ya. Practical zootomy of vertebrates.

3. Amphibians, reptiles. M., 1978. Terentyev P.V. Frog. M., 1950.

Carboniferous period

Seymouria

Anapsid group

Synapsid group.

Diapsid group

Scaly;
Turtles;
Crocodiles;
Beakheads.

hatteria,

Left a reply Guest

The body is divided into head, neck, torso, tail and five-fingered limbs.
The skin is dry, devoid of glands and covered with a horny covering that protects the body from drying out. The growth of the animal is accompanied by periodic molting.
The skeleton is strong and ossified. The spine consists of five sections: cervical, thoracic, lumbar, sacral and caudal. The shoulder and pelvic girdles of the limbs are strengthened and connected to the axial skeleton. The ribs and chest are developed.
The musculature is more differentiated than in amphibians. Developed cervical and intercostal muscles, subcutaneous muscles. The movements of the body parts are more varied and faster.
The digestive tract is longer than that of amphibians and is more clearly differentiated into sections. Food is captured by jaws with numerous sharp teeth. The walls of the mouth and esophagus are equipped with powerful muscles that push large portions of food into the stomach. At the border of the small and large intestines there is a cecum, especially well developed in herbivorous land turtles.
The respiratory organs - the lungs - have a large respiratory surface due to their cellular structure. Developed airways - trachea, bronchi, in which the air is moistened and does not dry out the lungs. Ventilation of the lungs occurs by changing the volume of the chest.
The heart is three-chambered, but the ventricle has an incomplete longitudinal septum, which prevents complete mixing of arterial and venous blood. Most of The body of reptiles is supplied with mixed blood with a predominance of arterial blood, therefore the metabolic rate is higher than that of amphibians.

What animals did reptiles come from? When did the ancestors of reptiles live?

However, reptiles, like fish and amphibians, are poikilothermic (cold-blooded) animals, whose body temperature depends on the temperature of their environment.
The excretory organs are the pelvic kidneys. Urine flows through the ureters into the cloaca, and from it into the bladder. In it, water is additionally sucked into the blood capillaries and returned to the body, after which urine is excreted. The end product of nitrogen metabolism, excreted in the urine, is uric acid.
The brain has a larger relative size than that of amphibians. The cerebral hemispheres of the forebrain with the rudiments of the cortex and cerebellum are better developed. The forms of behavior of reptiles are more complex. Sense organs are better adapted to a terrestrial lifestyle.
Fertilization is only internal. Eggs, protected from drying out by a leathery or shelled shell, are laid by reptiles on land. The embryo in the egg develops in a watery shell. Development is direct.

Origin of reptiles

Pedigree of reptiles

About 300 million

years ago the first amphibians appeared on Earth. However, already at the end of this period and beyond, the climate became dry again, and the descendants of the first amphibians began to develop in two directions. Some remained near the water and turned into modern amphibians. Others, on the contrary, began to adapt to the dry climate and turned into reptiles.

What changes have they made? First of all, a dense shell appeared on the eggs, so that they could be laid on land. In addition, the reptiles began to lay large eggs with a large amount of yolk. The development of the embryo lengthened, but what began to hatch was not a helpless larva, but a fully formed animal, differing from an adult only in its smaller size, already fully adapted to living conditions on land.

Adult reptiles also acquired the changes necessary for life on land. They have developed dense, keratinized skin that prevents evaporation. Oxygen does not pass through such skin. Therefore, the lungs have changed: they have acquired a cellular structure, that is, their working surface has greatly increased. In addition, ribs appeared, a chest was formed, and the breathing process became active by expanding and contracting the chest. A septum has appeared in the ventricle of the heart, although it is not completely complete, so that part of the blood mixes in it. The separation of venous and arterial blood in reptiles is much more perfect than in amphibians. However, they remain cold-blooded animals, their body temperature depends on the ambient temperature.

In the skeleton, along with the appearance of ribs, the cervical region greatly lengthened and the head became more mobile. When grasping prey, reptiles do not turn their whole body, as fish and amphibians do, but only turn their head. The senses have also improved. Of particular note is the improvement of the brain. Due to more varied movements, the cerebellum, which is responsible for the coordination of movements, has enlarged. The brain and sensory organs, as well as the behavior of reptiles, have a more complex structure compared to amphibians.

Ancient extinct reptiles - tyrannosaurus, tailed flying lizard, brontosaurus, ichthyosaur

The rise and extinction of ancient reptiles

So, reptiles became much more active and, not afraid to move away from the water, spread widely across the Earth. Gradually, many species emerged among them. The appearance of giant reptiles is especially characteristic of this time. Thus, some dinosaurs (“terrible lizards”) were up to 30 meters long and weighing up to 50 tons - the largest land vertebrates that ever existed on Earth. Such giants were even forced to return to a semi-aquatic lifestyle again - their mass decreases in water. They roamed shallow waters and fed on coastal and aquatic plants, reaching them with their long necks. There were also predators then, also very large, up to 10 meters long. Some reptiles that lived at that time even completely returned to an aquatic lifestyle, although they did not lose pulmonary respiration. Such, for example, was an ichthyosaur, or fish lizard, very similar in shape to a modern dolphin. Finally, there were flying lizards - pterodactyls.

Thus, reptiles have mastered all habitats - land, water and air. They formed many species and became the dominant animals on Earth.

But 70-90 million years ago, the climate on most of the Earth changed dramatically and became cold. At the same time, there became more diverse species of warm-blooded mammals - competitors of reptiles. This led to the fact that most reptiles, primarily all giant forms, became extinct, since giants cannot hide in shelters for the winter. Few reptiles have survived to this day - turtles, crocodiles, lizards and snakes. By the way, among them the largest ones are found only in warm countries and lead an aquatic or semi-aquatic lifestyle.

Origin and evolution of reptiles. Brief characteristics of the main groups of fossil reptiles.

The appearance of reptiles on Earth is the greatest event in evolution.

It had enormous consequences for all of nature. The origin of reptiles is one of the important questions in the theory of evolution, the process as a result of which the first animals belonging to the class Reptilia appeared. The first terrestrial vertebrates arose in the Devonian (more than 300 million years ago). These were armored-headed amphibians - stegocephalians. They were closely associated with bodies of water, since they reproduced only in water and lived near 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

Seymouria

All reptiles can be divided into three groups:

1) anapsids - with a solid cranial shell (cotylosaurs and turtles);

2) synapsids - with one zygomatic arch (animal-like, plesiosaurs and, possibly, ichthyosaurs) and

3) diapsids - with two arches (all other reptiles).

Anapsid group is the oldest branch of reptiles that have many common features in their skull structure with fossil stegocephalians, since not only many of their early forms (cotylosaurs), but even some modern ones (some turtles) have a solid cranial shell. Turtles are the only living representatives of this ancient group of reptiles. They apparently separated directly from the cotylosaurs. Already in the Triassic, this ancient group was fully formed and, thanks to its extreme specialization, has survived to the present day, almost unchanged, although in the process of evolution, some groups of turtles switched several times from a terrestrial lifestyle to an aquatic one, and therefore they almost lost their bony shields , then acquired them again.

Synapsid group. Marine fossil reptiles - ichthyosaurs and plesiosaurs - separated from the group of cotylosaurs. Plesiosaurs (Plesiosauria), related to synaptosaurs, were marine reptiles. They had a wide, barrel-shaped, flattened body, two pairs of powerful limbs modified into swimming flippers, a very long neck ending in a small head, and a short tail. The skin was bare. Numerous sharp teeth sat in separate cells. The sizes of these animals varied over a very wide range: some species were only half a meter in length, but there were also giants that reached 15 m. while plesiosaurs, having adapted to aquatic life, still retained the appearance of terrestrial animals, ichthyosaurs (Ichthyosauria), belonging to ichthyopterygians, acquired similarities with fish and dolphins. The body of ichthyosaurs was spindle-shaped, the neck was not pronounced, the head was elongated, the tail had a large fin, and the limbs were in the form of short flippers, with the hind ones being much smaller than the front ones. The skin was bare, numerous sharp teeth (adapted to feeding on fish) sat in a common groove, there was only one zygomatic arch, but of an extremely unique structure. The sizes varied from 1 to 13 m.

Diapsid group includes two subclasses: lepidosaurs and archosaurs. The earliest (Upper Permian) and most primitive group of lepidosaurs is the order Eosuchia. They are still very poorly studied; the best known is lounginia - a small reptile with a lizard-like physique, with relatively weak limbs that had the usual reptilian structure. Its primitive features are expressed mainly in the structure of the skull; teeth are located both on the jaws and on the palate.

There are now about 7,000 species of reptiles.

Reptiles are... Reptiles: photos

that is, almost three times more than modern amphibians. Living reptiles are divided into 4 orders:

Scaly;
Turtles;
Crocodiles;
Beakheads.

The most numerous order of squamates (Squamata), including about 6,500 species, is the only currently thriving group of reptiles, widespread throughout the globe and making up the bulk of the reptiles of our fauna. This order includes lizards, chameleons, amphisbaenas and snakes.

There are significantly fewer turtles (Chelonia) - about 230 species, represented in the animal world of our country by several species. This is a very ancient group of reptiles that has survived to this day thanks to a kind of protective device - the shell in which their body is encased.

Crocodiles (Crocodylia), of which about 20 species are known, inhabit continental and coastal waters of the tropics. They are direct descendants of ancient, highly organized reptiles of the Mesozoic.

The only species of modern rhynchocephalia, the tuateria has many extremely primitive features and is preserved only in New Zealand and on the adjacent small islands.

Reptiles have lost their dominant position on the planet mainly due to competition with birds and mammals against the background of a general cooling, which is confirmed by the current ratio of the number of species of different classes of terrestrial vertebrates. If the share of amphibians and reptiles that are most dependent on environmental temperature is quite high on a planetary scale (10.5 and 29.7%), then in the CIS, where the area of warm regions is relatively small, they are only 2.6 and 11.0% .

Reptiles, or reptiles, of Belarus represent the northern “outpost” of this diverse class of vertebrate animals. Of the more than 6,500 species of reptiles now living on our planet, only 7 are represented in the republic.

In Belarus, which does not have a warm climate, there are only 1.8% of reptiles and 3.2% of amphibians. It is important to note that the decrease in the proportion of amphibians and reptiles in the fauna northern latitudes occurs against the background of a decrease in the total number of species of terrestrial vertebrates. Moreover, out of four orders of modern reptiles, only two (turtles and squamates) live in the CIS and Belarus.

The Cretaceous period was marked by the collapse of reptiles and the almost complete extinction of dinosaurs. This phenomenon poses a mystery to science: how does a huge, prosperous, all-occupying ecological niches an army of reptiles that ranged from the tiniest creatures to unimaginable giants, so suddenly went extinct, leaving only relatively small animals?

It was these groups that at the beginning of the modern Cenozoic era occupied a dominant position in the animal world. And among reptiles, out of 16-17 orders that existed during their heyday, only 4 survived. Of these, one is represented by the only primitive appearance — hatteria, preserved only on two dozen islands near New Zealand.

The other two orders - turtles and crocodiles - unite a relatively small number of species - about 200 and 23, respectively. And only one order - squamates, which includes lizards and snakes, can be assessed as thriving in the current evolutionary era. This is a large and diverse group, numbering more than 6,000 species.

Reptiles are distributed throughout the globe, except Antarctica, but extremely unevenly. If their fauna is most diverse in the tropics (in some regions there are 150-200 species), then only a few species penetrate into high latitudes (in Western Europe only 12).

Origin and evolution of reptiles. Brief characteristics of the main groups of fossil reptiles.

The appearance of reptiles on Earth is the greatest event in evolution.

Carboniferous period

Seymouria

All reptiles can be divided into three groups:

1) anapsids - with a solid cranial shell (cotylosaurs and turtles);

2) synapsids - with one zygomatic arch (animal-like, plesiosaurs and, possibly, ichthyosaurs) and

3) diapsids - with two arches (all other reptiles).

Origin of reptiles

IN while plesiosaurs, having adapted to aquatic life, still retained the appearance of terrestrial animals, ichthyosaurs (Ichthyosauria), belonging to ichthyopterygians, acquired similarities with fish and dolphins. The body of ichthyosaurs was spindle-shaped, the neck was not pronounced, the head was elongated, the tail had a large fin, and the limbs were in the form of short flippers, with the hind ones being much smaller than the front ones. The skin was bare, numerous sharp teeth (adapted to feeding on fish) sat in a common groove, there was only one zygomatic arch, but of an extremely unique structure. The sizes varied from 1 to 13 m.

There are now about 7,000 species of reptiles, almost three times as many as modern amphibians. Living reptiles are divided into 4 orders:

Scaly;
Turtles;
Crocodiles;
Beakheads.

Crocodiles (Crocodylia), of which about 20 species are known, inhabit continental and coastal waters of the tropics. They are direct descendants of ancient, highly organized reptiles of the Mesozoic.

The only species of modern rhynchocephalia, the tuateria has many extremely primitive features and is preserved only in New Zealand and on the adjacent small islands.

In Belarus, which does not have a warm climate, there are only 1.8% of reptiles and 3.2% of amphibians. It is important to note that the decrease in the proportion of amphibians and reptiles in the fauna of northern latitudes occurs against the background of a decrease in the total number of species of terrestrial vertebrates. Moreover, out of four orders of modern reptiles, only two (turtles and squamates) live in the CIS and Belarus.

The Cretaceous period was marked by the collapse of reptiles and the almost complete extinction of dinosaurs. This phenomenon poses a mystery to science: how did a huge, thriving army of reptiles occupying all ecological niches, which had representatives from the tiniest creatures to unimaginable giants, so suddenly become extinct, leaving only relatively small animals?

It was these groups that at the beginning of the modern Cenozoic era occupied a dominant position in the animal world. And among reptiles, out of 16-17 orders that existed during their heyday, only 4 survived. Of these, one is represented by a single primitive species - hatteria, preserved only on two dozen islands near New Zealand.

$mob_info$