Ancient reptiles: origin and extinction. The origin of reptiles Reptiles are ... Reptiles: photo

Reptiles have their origins in the Paleozoic, when in the Carboniferous they separated from the ancient stegocephalic amphibians. The diverse evolution of reptiles, resulting in a complex picture of adaptations to various conditions of existence, lasted a very long time: G. F. Osborn (1930) is inclined to determine the duration of this process as 15-20 million years.

Rice. 1. Skull and lower jaw of Therocephalia: Scylacosaurns sclateri ( BUT) and Cynognathus crateronotus ( AT) from Perm ( BUT) and Triassic (AT) South Africa. The first of the early Therocephalia, the second of Cynodontia.

1-praemaxillare; 2-septomaxiliare; 3-maxillare; 4-nasal; 5-frontale; 6-lacrymale; 7-adlacrymale; 8-postfrontal; 9 postorbital; 10-parietale; 11-jugale; it-squamosum; 13-square; 1 4-den-tale; 15-angu-lare; 16-supraangulare; 17 articulare; 18-Inferior temporal fossa.

Due to various conditions, some of which are only difficult to take into account due to the plasticity of organization, environmental influences and a number of other reasons, reptiles have undergone a complex evolution in the history of their development. They took possession of a diverse environment: land, water, air, and in the development of some groups, as we will see later, some returns of adaptations to the living environment that was once dominant for this group (for example, among sea turtles) were observed.

Due to the large number and diversity of individuals, the taxonomy of extinct reptiles presents significant difficulties and lacks unity. So, F. Broili, E. Koken and M. Schlosser (1911) number 10 orders of extinct and recent reptiles, M. V. Pavlova (1929) -13, G. F. Osborn (1930) - 18, Abel (1924) -20.

Rice. 2. Thaumatosaurus victor, plesiosaurus, 3.44 m long from the Upper TriassicSouthNoah Germany.

First of all, it should be noted that the differences between these "orders" are so striking and significant [suffice it to point out, for example, to the heifer cranial (Cotylosauria), the helmet cranial (Pelycosauria) or ichthyosaurs and plesiosaurs] that for the taxonomy of recent animals it becomes the obvious inevitability of a sharper taxonomic differentiation. Many of the above detachments, in our opinion, are more correct and natural to consider as subclasses. True, in some systems a unifying grouping into subclasses is accepted based on the structure of the temporal pits and arches (Anapsida, Diapsida, Syn,apsida and Parapsida). However, quite a few fairly weighty objections can be raised against the rationality of such a division.

The temporal region of the skull during the evolution of one group, for example, in turtles, has undergone such significant changes that, on the basis of purely external morphological features (without taking into account the picture of the evolutionary process), one of the turtles (modern marine ones with a continuous wall of the temporal region) must be attributed to Anapsida, others to Synapsida. With systematic divisions, we are based primarily on specific, existing morphological characters, and not on speculative data of an evolutionary process that has not yet been fully identified. Therefore, varying even in a smallgroup, the structure of the temporal region cannot serve as a criterion for establishing subclasses, as M.V. Pavlova (1929) does, but only as a control auxiliary feature for analyzing the process of development of the diverse branches of reptiles.

An overview of some subclasses and phylogenetic relationships with other vertebrates. The most primitive group is made up of a subclass of cauldron-cranied (Cotylosauria), distinguished by a quilted skull, clumsy rather high five-fingered limbs, and amphicoelous vertebrae. The first representatives of this subclass, undoubtedly related to stegocephalic amphibians, appear already in the Upper Carboniferous deposits, reach a special flowering in the Permian deposits and end their existence in the Triassic.

The best-known representatives of this subclass are the Pareiasauras, which in a significant number of forms were first known from the slates and sandstones of the Permian layers of the Karoo Formation (in southern Africa). In relatively recent times, many skulls and skeletons of pareiasaurs were discovered by prof. V. P. Amalitsky on the Northern Dvina. They were large, massive forms. For example, the length of the skeleton of P. karpinskii reaches 2 m 45 cm, the length of the skull of this animal is 48 cm. The labidosaurus (Labidosaurus hamatus), a small (up to 70 cm long), short-tailed animal from the Permian deposits of Texas, had a peculiar appearance.

Rice. Fig. 3. Reconstruction of the skeleton of Eunnotosaurus africanus from the Permian layers (reduced).

Helmet-headed reptiles (Pelyeosauria)

Belonged to Varanops from the Lower Permian deposits of Texas. It was a mobile long-tailed animal. Osborne is inclined to consider him the prototype of the wholea number of further reptiles: alligators, lizards, dinosaurs. Some extremely specialized forms belong to the subclass mentioned, for example, Dimetrodon gigas from the Permian deposits of Texas, a predatory reptile in which the upper processes of the dorsal vertebrae were extremely elongated. Between these processes, a skin fold was probably stretched, giving the animal a completely unusual appearance.

Subclass of belief-like reptiles (Theromorpha)

Dividing into at least three orders (Fig. 1), it is especially interesting in terms of the structure of heterodoitic teeth differentiated into groups, canines and molars. Further it may be noted; development of the coronoid process on the lower jaw, the presence of a double condyle in the occipital region of the skull for articulation by the vertebrae.

Rice. 4. Armor of Thalassemys marina (Upper Jurassic).

Some animal-like species reached a significant size, for examplemeasures, Inostrancevia alexandri, up to 3 m long. Many remains of several species of Theromorpha were obtained by the expedition of prof. V. P. Amalitsky on the Northern Dvina.

According to the location of the remains of skeletons, it can be assumed that they are concentratedtraversed along the edges of the ancient channelvanished river. In addition to the finds of Severodvinsk reptiles, the closest relatives of these reptiles were found in the Permian layers.North America and in the Karoo layers of southern Africa. These data show that the ancient Permian animal-like fauna was relatively uniform.

Rice. 5. Carapace and skeleton of Archelon chyros (Upper Cretaceous, North America).

An extremely specialized subclass consisted of ichthyosaurs (Ichthyosauri a), marine animals with a naked fusiform body, a narrow elongated snout, and reduced hind limbs; their forelimbs have turned into long flippers. On the back are sharp fins similar to shark fins; tail with a bilobed shark-type fin. The skull has one pair of temporal arches; on the jaws a large number of sharp cone-shaped teeth.

Ichthyosaurs, as the history of their development shows, evolved from terrestrial forms; later on, the species, adapted to pelagic life, again returned to the station of a low-lying existence, and the females laid their eggs on the sands near the shallows. Then a secondary process of adaptation took place, and these animals, which arose from the Triassic, ended their existence in the Cretaceous epoch in the form of true inhabitants of the open sea, and they developed an important adaptive feature - live birth. Thanks to the ability to swim for a long time, ichthyosaurs made huge migrations.tions. Osborn (1930) determines the length of such journeys from the coast of Svalbard to the Antarctic zone.

Rice. 6. DiploclocTis carnegii - diplodocus from the Upper Jurassic of North America

A peculiar subclass of marine animals corresponded to plesiosaurs(Piesiosauria; Fig. 2), who lived from the Triassic to the Upper Cretaceous. They were distinguished by pasty limbs, variously developed dentition, adapted to gnaw hard shells of mollusks. In the skull, only one pair of temporal holes is characteristic, in the spine, the presence of weakly amphicoelous, almost platycoelous vertebrae. The length of the neck varied: in many species (Elasmosaurus), the neck reached an enormous length and contained up to 76 vertebrae. The ratio of the length of the neck to the length of the body, which reached 3 m, was 23:9. In other forms, such as the Cretaceous Brachauchenius, the neck was shortened and contained only 13 vertebrae. Body sizes varied greatly. Along with relatively small animals 1.5 m long (Plesiosaurus macrocephalus), giants 13 m long (Elasmosaurus) came across.

We now turn to a brief review of the evolution of turtles (Chelonia). Some authors consider the ancestor of the Triassic turtle Placodus gigas, cloud which gave flat teeth, relatively small on the jaws and especially wide and large in the palate. the occipital condyle was absent in the skull of the placodus, and the processes of the occipital bones entered the corresponding depressions of the first cervical vertebra. All these distinctive features make Placodus quite apart.

Apparently, Eunnotosaurus africanus (Fig. 3) from the Permian layers of the Cape colony of Africa can be considered the initial form for turtles. In this remarkable reptile, the 8 middle thoracic ribs are extremely widened, their edges adjoin each other and form, as it were, a bone shield. Eunnotos aurus also has teeth on the jaws and palate; this animal led a life similar to that of terrestrial turtles.

Already in the Triassic, cryptocervical ones arose. Their evolution is full of deep interest. Probably, in the Jurassic, a group separated from terrestrial turtles, first adapted to life in the coastal zone, and then gradually moved to the open sea. In this regard, in these turtles, the dorsal armor became simpler, which, in addition, became lighter due to the development of marginal cuts; the ventral armor lost its integrity and received a significant fountain in the middle part (in Thalassemys marina from the Upper Jurassic deposits; Fig. 4). This process of armor reduction has advanced considerably in undoubted forms of the open sea, such as in the North American Upper Cretaceous Archelonis (Fig. 5). In a high degreeresno, that in early Tertiary time, a branch separated from these pelagic formsinhabitants of the coastal zone. They have a shell again becomes more array nym and is composed of small polygonal plates. These coastal dwellers changed the littoral station for the second time to pelagic, which in its turn caused a secondary reduction of the shell. In modern skin and pto ya, a descendant of secondary migrants, the reduced carapace contains derivatives of the primary and secondary leg skeletons. But in any case, the shell of turtles that have again switched to life on the high seas is built according to a different principle than that of the ancient pelagic species. In 1803, Louis Dollo formulated the law of the irreversibility of the evolutionary process. According to this law, any branch of animals, having taken a certain direction in its specialization, can in no case go back along the same path. In the case described, we have, as it were, a repetition of the evolutionary process. However, it should be emphasized that although adaptations in turtles to the pelagic environment for the second time caused a number of corresponding changes in the animal organism, nevertheless, the picture of the evolution of morphological characters was different in this case and did not follow the old path.

Higher it was pointed to the antiquity of lizards(Rhynchocephalia). Here in addition to history of this subclass, it can be indicated that the most ancient representatives(Palaeohatteria longicaudata) are known from the Lower Permian layers near Dresden and that this subclass has survived to this day in the person of a single recent representative.

Rice. 7. Brontosaurus excelsus (Lower Cretaceous, North America)

The subclass of crocodiles has its roots in the Triassic. Primary forms of crocodiles (for example, Scleromochlus taylori) differed in small size,tail length, shortened with a sharp muzzle. In terms of distribution, the extinct ones were confined to freshwater bodies, although purely pelagic species (Jurassic Teleosauridae and Geosauridae) were also encountered.

From the Triassic to the Upper Cretaceous, representatives of the subclass of dinosaurs (Dinosauria) lived - a heterogeneous group that breaks up into several orders. They are characterized by the presence of two pairs of temporal arches. They varied in size and appearance; some representatives reached the size of a domestic cat,others are of enormous length, more than 20 m. Giants, like the brontosaurus (Brontosaurus excelsus, Fig. 7) or diplodocus (Diplodocus carnegii, Fig. 6), both from the Upper Jurassic, were distinguished by an enormous neck and tail length, were herbivorous and moved slowly on four limbs. Other species, such as the Jurassic North American Ceratosaurus (Ceratosaurus nasicornis) or Tyrannosaurus Rex (Tugappo-saurus rex), were real predators. Guanodonts, huge herbivorous reptiles that walked on massive hind limbs, also made up a peculiar detachment. The skeleton of the huge Trachodon amurensis was found near Blagoveshchensk (on the Amur) and restored by prof. N. A. Ryabinin. Concluding our brief review of this subclass, let's mention the stegosaurs, which were characterized by the presence of large bony plates and spikes located along the back and tail.

Rice. 8. Pterodactylus spectabilis (Jurassic)

Dinosaurs, so abundantly represented, died out without a trace. The reasons for the death of this group are largely unclear. It is possible that the factors of processes of deep, excessive specialization and growth growth played their role here (S. Depere,1915), which led to the loss of plasticity and adaptability to the life conditions that continued to gradually change. It is possible that there was also a vital competition with other more adapted organisms.

The Jurassic and Cretaceous winged lizards (Pterosauria), which comprised two orders: rhamphorhynchus and pterodactyls, constituted a completely peculiar subclass (Fig. 8). In these reptiles, forelimbs with a very elongated fifth finger and the presence of real flying membranes on narrow, long, sharp wings have reached extreme specialization. The tail varied in length; in some forms it was reduced. The skull was elongated, sometimes beak-shaped; teeth of thecodont type or completely absent. Some forms were distinguished by a huge wingspan (in Pteranodon, up to 7 m). The paleontological history of the modern most species-rich subclass of squamates (Squamata) is relatively poorly understood. Authentic ancestor this group can be considered the Permian Araeoscelis gracilis. (Relationship diagram see Fig. 9).

Rice. 9. Scheme of the evolutionary development of reptiles and related relationships of various groups.

Major subclasses of extinct and modern reptiles

Subclass 1. Cauldron-Cranial-Cotylosauria (Permian-Triassic).

2. Helmet-Cranial-Pelycosauria (Permian-Triassic).

»3. Animal-Theromorpha (Permian-Triassic).

» 4. Ichthyosaurs-Ichthyosauria (Triassic-Cretaceous).

"5. Plesiosaurs-Plesiosauria (Triassic-Upper Cretaceous).

»6. The lamellar tooth is Placodontia (Triassic).

»7. Lizards-Rhynchocephalia (from the Lower Permian to the present).

"eight. Turtles-Chelonia (from Permian and Triassic to modern)

"nine. Crocodiles-Crocodilia (from Triassic to modern).

"ten. Dinosaurs-Dinosauria (Triassic to Upper Cretaceous).

"eleven. Winged lizards - Pterosauria (Jurassic).

"12. Scaly-Squamata (from Permian to modern).

Article on the topic of reptile evolution

Origin of reptiles

Origin of reptiles- one of the important questions in the theory of evolution, the process as a result of which the first animals belonging to the class Reptiles (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 ways, they are still very close to stegocephals. Their skull was in the form of a solid bone box with holes 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; in the shoulder girdle, a kleytrum was preserved - a skin bone characteristic of fish; 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 have become more mobile; their skeleton became lighter, but at the same time stronger. Reptiles used a more varied diet than amphibians. The technique of obtaining it has changed. In this regard, the structure of the limbs, the axial skeleton and the skull underwent significant changes. Most of the limbs became longer, the pelvis, acquiring stability, was attached to two or more sacral vertebrae. In the shoulder girdle, the "fish" bone of the kleytrum disappeared. The solid shell of the skull has undergone a partial reduction. In connection with the more differentiated muscles of the jaw apparatus in the temporal region of the skull, pits and bone bridges separating them appeared - arcs that served to attach a complex system of muscles.

synapsids

The main ancestral group that gave all the variety of modern and fossil reptiles were cotylosaurs, however, the further development of reptiles went in different ways.

Diapsides

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 extremely wide adaptive radiation to systematic groups and species, which are found both among extinct forms and among modern reptiles. Among the diapsids, there are two main groups of Lepidosauromorphs (Lepidosauromorpha) and Archosauromorphs (Archosauromorpha). The most primitive diapsids from the Lepidosaur group are the Eosuchia order ( Eosuchia) - were the ancestors of the order Beakheads, of which only one genus is currently preserved - tuatara.

At the end of the Permian, scaly ones (Squamata) separated from primitive diapsids, which became numerous in the Cretaceous period. Towards the end of the Cretaceous, snakes evolved from lizards.

Origin of archosaurs

see also

• Temporal arches

Notes

Literature

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

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

It had tremendous consequences for all of nature. The origin of reptiles is one of the important questions in the theory of evolution, the process that resulted in the appearance of the first animals belonging to the class Reptiles (Reptilia). The first terrestrial vertebrates arose in the Devonian (more than 300 million years ago). These were shell-headed amphibians - stegocephals. They were closely associated with water bodies, since they bred only in water, lived near water. The development of spaces remote from water bodies required a significant restructuring of the organization: adaptation to protecting the body from drying out, to breathing atmospheric oxygen, efficient movement on a solid substrate, and the ability to reproduce outside water. These are the main prerequisites for the emergence of a qualitatively different group of animals - reptiles. These restructurings were quite complex, for example, it required the design of powerful lungs, 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 (cotilosaurs and turtles);

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

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

Anapsid group is the oldest branch of reptiles, which, in terms of the structure of the skull, have many features in common with fossil stegocephalians, since not only many of their early forms (cotilosaurs), 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 diverged directly from cotylosaurs. Already in the Triassic, this ancient group was fully developed and, thanks to its extreme specialization, has survived to the present, almost unchanged, although in the process of evolution, some groups of turtles several times switched from a terrestrial to aquatic lifestyle, due to which they almost lost their bone shields then bought them again.

synapsid group. Marine fossil reptiles - ichthyosaurs and plesiosaurs - separated from the group of cotilosaurs. 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 within a very wide range: some species were only half a meter long, 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 fusiform, the neck was not expressed, the head was elongated, the tail had a large fin, the limbs were in the form of short flippers, and the hind ones were much smaller than the front ones. The skin was bare, numerous sharp teeth (adapted to feeding on fish) sat in a common furrow, there was only one zygomatic arch, but of an extremely peculiar 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 understood, better known than others are lounginia - a small reptile resembling a lizard in physique, with relatively weak limbs that had the usual reptilian structure. Its primitive features are expressed mainly in the structure of the skull, the teeth are located both on the jaws and on the palate.

Now there are about 7,000 species of reptiles, that is, almost three times more than modern amphibians. Living reptiles are divided into 4 orders:

· scaly;

· Turtles;

· Crocodiles;

· Beakheads.

The most numerous squamous order (Squamata), which includes about 6,500 species, is the only now thriving group of reptiles, widespread throughout the globe and constituting the bulk of the reptiles of our fauna. This order includes lizards, chameleons, amphisbaenas and snakes.

There are much 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 - a shell in which their body is chained.

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

The only species of modern beakheads (Rhynchocephalia) - the tuatara has many extremely primitive features and has survived 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 also confirmed by the current ratio of the number of species of different classes of terrestrial vertebrates. If the share of amphibians and reptiles, which are the most dependent on the environmental temperature, on a global scale is quite high (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 vertebrates. 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 differ in the warmth of the climate, there are only 1.8 reptiles, 3.2% 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, in the CIS and Belarus, out of four orders of modern reptiles, only two (tortoises and scaly ones) live.

The Cretaceous period was marked by the collapse of the reptiles, the almost complete extinction of the dinosaurs. This phenomenon is a mystery to science: how did a huge, prosperous, ecologically niche army of reptiles, which included representatives from the smallest creatures to unimaginable giants, so suddenly died out, 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 kingdom. And among the reptiles out of 16-17 orders that existed during their heyday, only 4 survived. Of these, one is represented by the only primitive species - tuatara, preserved only on two dozen islands near New Zealand.

Two other orders - turtles and crocodiles - unite a relatively small number of species - about 200 and 23, respectively. And only one order - scaly, which includes lizards and snakes, can be assessed as flourishing in the current evolutionary era. This is a large and diverse group, numbering more than 6000 species.

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

Dinosaurs, brontosaurs, ichthyanosaurs, pterosaurs - these and many other relatives of them are known to modern people thanks to archaeological excavations. At different times in different regions, separate fragments of the skeletons of ancient reptiles were found, according to which scientists scrupulously restored the appearance and lifestyle of archaic animals. Today, the remains of reptiles can be admired in many museums around the world.

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 covering of the body, covered with a dense layer of horn 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 falls on the Mesozoic era. Archaic pangolins 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 the emergence of ancient reptiles

The reason for the emergence of archaic lizards was a change in climatic conditions. Due to the cooling and drying of many water bodies, amphibians were forced to get out of their usual aquatic habitat on land. As a result of evolution, ancient reptiles appeared as a more perfect link in the lower vertebrates.

Climate change has caused major mountain building processes. Ancient amphibians had thin skin without a protective coating, underdeveloped internal organs, and imperfect lungs. Creatures reproduced mainly by spawning. This method of procreation could not be carried out on land due to the fragility of the future offspring. Lizards laid eggs with hard shells and endurance in changing climates.

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

• land animals (dinosaurs, theriodonts, tyrannosaurs, brontosaurs);
• swimming fish lizards (ichthyosaurs and plesiosaurs);
• flying (pterosaurs).

Types of ancient lizards

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

• Flying dinosaurs - pterodactyls, rhamphorhynchus, etc. The largest gliding lizard was pteranodon, whose wingspan reached 16 meters. A rather fragile body deftly moved through the air even in light winds thanks to a natural rudder - a bone crest on the back of the head.
• Aquatic reptiles - ichthyosaur, mesosaurus, plesiosaur. The food of the 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, molars. The most famous theriodonts are pterosaurs, dinosaurs, etc.

herbivores

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

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 testifies to the adaptation of archaic animals to pluck leaves located on the crown of tall trees: almost all herbivorous lizards had a long neck and a rather small head. The body of the "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 predatory reptiles, unlike their herbivorous relatives, were relatively small in size. The largest representative of the archaic carnivores is the tyrannosaurus rex, whose body reached 10 meters in length. Predators had strong large teeth and a rather intimidating 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 tighten. 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 lizards.

Another reason for the extinction of ancient reptiles is considered to be the spread of a large number of plants that are not suitable for food for dinosaurs. Poisonous grass killed many species of pangolins, 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 occupied by stronger animals - mammals and birds, warm-blooded and with a higher development of the brain.

In the Upper Triassic, from carnivores, moving mainly on their hind limbs, pseudosuchians (thecodonts); two more groups separated: lizards and ornithischians - dinosaurs that differ 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 a rabbit 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. Big part was a predator moving on its hind limbs (a heavy tail served as a counterweight); the forelimbs were shortened, often rudimentary. Among them there were giants up to 10-15 m long, armed with powerful teeth and strong claws on the fingers of their hind limbs, like a ceratosaurus; despite the big dimensions, these predators were very mobile. Part of the lizard dinosaurs switched to eating plant foods and moving on both pairs of limbs. These include the largest land animals that have ever existed. So, diplodocus, which had a long tail and a long, mobile neck, carrying a small head, was 30 m long and probably weighed about 20-25 tons, and a more massive and short-tailed brachiosaurus, with a length of about 24 m, probably weighed at least 50 tons. Such giants, apparently, moved slowly over land and most of the time, like modern hippos, stayed in the coastal areas of water bodies, eating aquatic and above-water plants. Here they were protected from the attack of large land predators, and their enormous weight made it possible to successfully withstand the blows of the waves.

Ornithischian dinosaurs were probably herbivores. Most of them retained a bipedal type of movement with noticeably shortened forelimbs. Among them, giants 10-15 m long arose, for example iguanodons, in which the first limb turned into a powerful spike, apparently helped defense against predators. Duck-billed dinosaurs stayed along the banks of water bodies and could run and swim. The front part of the jaws formed a wide duck-like beak, and in the depths of the mouth there were numerous flattened teeth that ground plant food. Other ornithischians, having retained herbivory, again returned to the four-legged walking. They often developed protective education against large predators. So, in a stegosaurus that reached 6 m - on back there were two rows of large bone triangular plates, and on a powerful tail there were sharp bone spikes more than 0.5 m long. Triceratops had a powerful horn on the nose and on the horn above the eyes, a the widened posterior edge of the skull that protected the neck bore numerous pointed processes.

Finally, the last branch of reptiles - a subclass of animal-like, or synapsids - was almost the first to separate from the common trunk of reptiles. They separated themselves from the primitive Carboniferous cotylosaurs, which apparently inhabited humid biotopes and still retained many amphibian features (skin rich in glands, structure of the limbs, etc.). Synapsids began a special line of development of reptiles. Already in the Upper Carboniferous and Permian, various forms arose, united in the order of pelycosaurs. They are had amphicoelous vertebrae, a skull with a poorly developed one fossa and one occipital condyle, there were also teeth on the palatine bones, there were ventral ribs. In appearance, they looked like lizards, their length did not exceed 1 m; only single species reached 3-4 m in length. Among them were real predators and herbivorous forms; many led a terrestrial way of life, but there were near-aquatic and aquatic forms.

To end perm pelycosaurs died out, but earlier the animal-toothed reptiles, therapsids, separated from them. The adaptive radiation of the latter proceeded in the Upper Permian, 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 - foreigners (skull length 50 cm) and others. Some small forms, like rodents, had large incisors and, apparently, led a burrowing lifestyle. By the end of the Triassic and the beginning of the Jurassic, diversely and well-armed archosaurs had completely replaced the animal-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 - the beginning of the Triassic, a diverse fauna of reptiles (approximately 13-15 orders) had developed, displacing most groups of amphibians. The flowering of reptiles was secured a number of aromorphoses that affected all organ systems and ensured an increase in mobility, intensification of metabolism, greater resistance to a number of environmental factors (to dryness in the first place), some complication of behavior and better survival of offspring. The formation of the temporal pits was accompanied by an increase in the mass of chewing muscles, which, along with other transformations, made it possible to expand the range of feeds used, especially plant foods. Reptiles not only widely mastered the land, populating a variety of habitat, but returned to the water and rose into the air. Throughout the Mesozoic era - for more than 150 million years - they occupied the dominant position in almost all terrestrial and many aquatic biotopes. At the same time, the composition of the fauna changed all the time: the ancient groups were dying out, being replaced by more specialized young forms.

By the end of the Cretaceous period on earth started a new powerful cycle of mountain building (Alpine), accompanied by extensive transformations of landscapes and the redistribution of seas and land, an increase in the general dryness of the climate and an increase in its contrasts both in seasons of the year and and by natural areas. At the same time, vegetation changed: the dominance of cycads and conifers is replaced by the dominance of angiosperms, whose fruits and seeds have a high stern value. These changes could not but affect the animal world, especially since by this time two new classes of warm-blooded vertebrates had already formed - mammals and birds. The specialized groups of large reptiles that survived to this time could not adapt to the changing conditions of life. In addition, increasing competition with smaller but active birds and mammals played an active role in their extinction. These classes, having acquired warm-bloodedness, persistently high metabolic rates, and more complex behavior, have increased in numbers and importance in communities. They quickly and efficiently adapted to life in changing landscapes, more quickly mastered new habitats, intensively used new food and exerted an increasing competitive impact 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 (lizards and snakes), well-protected turtles survived and a small group of aquatic archosaurs - crocodiles.

Literature: Zoology of vertebrates. Part 2. Reptiles, birds, mammals. Naumov N. P., Kartashev N. N., Moscow, 1979