The Mesozoic era began approximately 250 and ended 65 million years ago. It lasted 185 million years. The Mesozoic era is divided into the Triassic, Jurassic and Cretaceous periods with a total duration of 173 million years. The deposits of these periods constitute the corresponding systems, which together form the Mesozoic group.
The Mesozoic is known primarily as the era of dinosaurs. These giant reptiles overshadow all other groups of living beings. But you shouldn’t forget about others. After all, it was the Mesozoic - the time when real mammals, birds, and flowering plants appeared - that actually formed the modern biosphere. And if in the first period of the Mesozoic - the Triassic, there were still many animals on Earth from Paleozoic groups that were able to survive the Permian catastrophe, then in the last period - the Cretaceous, almost all those families that flourished in the Cenozoic era had already formed.
The Mesozoic era was transition period in development earth's crust and life. It can be called the geological and biological Middle Ages.
The beginning of the Mesozoic era coincided with the end of the Variscan mountain-building processes; it ended with the beginning of the last powerful tectonic revolution - the Alpine folding. In the Southern Hemisphere, the Mesozoic saw the end of the collapse of the ancient continent of Gondwana, but overall the Mesozoic era here was an era of relative calm, only occasionally and briefly disrupted by slight folding.
The progressive flora of gymnosperms (Gymnospermae) became widespread already from the beginning of the Late Permian era. The early stage of development of the plant kingdom - paleophyte, was characterized by the dominance of algae, psilophytes and seed ferns. The rapid development of more highly developed gymnosperms, which characterizes the “plant Middle Ages” (mesophyte), began in the Late Permian era and ended at the beginning of the Late Cretaceous era, when the first angiosperms, or flowering plants (Angiospermae), began to spread. The Cenophyte began in the Late Cretaceous - modern period development of the plant kingdom.
The appearance of gymnosperms was an important milestone in the evolution of plants. The fact is that earlier Paleozoic spore-bearing plants needed water or, at least, a humid environment for their reproduction. This made their resettlement quite difficult. The development of seeds allowed plants to lose such close dependence on water. The ovules could now be fertilized by pollen carried by the wind or insects, and water thus no longer determined reproduction. In addition, unlike a single-celled spore with its relatively small supply of nutrients, the seed has a multicellular structure and is able to provide food for a young plant in the early stages of development for longer. Under unfavorable conditions, the seed can remain viable for a long time. Having a durable shell, it reliably protects the embryo from external dangers. All these advantages gave seed plants good chances in the struggle for existence. The ovule (ovum) of the first seed plants was unprotected and developed on special leaves; the seed that emerged from it also did not have an outer shell. This is why these plants were called gymnosperms.
Among the most numerous and most curious gymnosperms of the beginning of the Mesozoic era we find the Cycas, or sago. Their stems were straight and columnar, similar to tree trunks, or short and tuberous; they bore large, long and usually feathery leaves
(for example, the genus Pterophyllum, whose name means “feathery leaves”). Outwardly, they looked like tree ferns or palm trees.
In addition to the cycads, the Bennettitales, represented by trees or shrubs, became of great importance in the mesophyte. They mostly resemble true cycads, but their seed begins to develop a tough shell, which gives Bennettites an angiosperm-like appearance. There are other signs of adaptation of Bennettites to conditions of a drier climate.
In the Triassic, new forms came to the fore. Conifers are spreading quickly, and among them are firs, cypresses, and yews. Among the ginkgos, the genus Baiera has become widespread. The leaves of these plants had the shape of a fan-shaped plate, deeply dissected into narrow lobes. Ferns have taken over damp, shady places along the banks of small bodies of water (Hausmannia and other Dipteraidae). Forms that grow on rocks (Gleicheniacae) are also known among ferns. Horsetails (Equisetites, Phyllotheca, Schizoneura) grew in the swamps, but did not reach the size of their Paleozoic ancestors.
In the middle mesophyte (Jurassic period), the mesophytic flora reached the culmination point of its development. The hot tropical climate in what is now the temperate zone was ideal for tree ferns to thrive, while smaller fern species and herbaceous plants preferred the temperate zone. Among the plants of this time, gymnosperms continue to play a dominant role
(primarily cycads).
The Cretaceous period is marked by rare changes in vegetation. The flora of the Lower Cretaceous still resembles in composition the vegetation of the Jurassic period. Gymnosperms are still widespread, but their dominance ends at the end of this time. Even in the Lower Cretaceous, the most progressive plants suddenly appeared - angiosperms, the predominance of which characterizes the era of new plant life, or Cenophyte.
Angiosperms, or flowering plants (Angiospermae), occupy the highest level of the evolutionary ladder flora. Their seeds are enclosed in a durable shell; there are specialized reproductive organs (stamen and pistil) assembled into a flower with bright petals and a calyx. Flowering plants appear somewhere in the first half of the Cretaceous period, most likely in a cold and dry mountain climate with large temperature differences.
With the gradual cooling that marked the Cretaceous, they captured more and more new areas on the plains. Quickly adapting to their new environment, they evolved at amazing speed. Fossils of the first true angiosperms are found in the Lower Cretaceous rocks of Western Greenland, and a little later also in Europe and Asia. In a relatively short time, they spread throughout the Earth and reached great diversity.
From the end of the Early Cretaceous era, the balance of forces began to change in favor of angiosperms, and by the beginning of the Upper Cretaceous their superiority became widespread. Cretaceous angiosperms belonged to the evergreen, tropical or subtropical types, among them were eucalyptus, magnolia, sassafras, tulip trees, Japanese quince trees, brown laurels, walnut trees, plane trees, and oleanders. These heat-loving trees coexisted with the typical flora of the temperate zone: oaks, beeches, willows, and birches. This flora also included gymnosperms conifers (sequoias, pines, etc.).
For gymnosperms, this was a time of surrender. Some species have survived to this day, but their total numbers have been declining all these centuries. A definite exception is conifers, which are still found in abundance today.
In the Mesozoic, plants made a great leap forward, surpassing animals in terms of development rates.
Mesozoic invertebrates were already approaching modern ones in character. A prominent place among them was occupied by cephalopods, to which modern squids and octopuses belong. The Mesozoic representatives of this group included ammonites with a shell twisted into a “ram’s horn”, and belemnites, the inner shell of which was cigar-shaped and overgrown with the flesh of the body - the mantle. Belemnite shells are popularly known as “devil’s fingers.” Ammonites were found in such numbers in the Mesozoic that their shells are found in almost all marine sediments of this time. Ammonites appeared in the Silurian, they experienced their first flowering in the Devonian, but reached their highest diversity in the Mesozoic. In the Triassic alone, over 400 new genera of ammonites arose. Particularly characteristic of the Triassic were ceratids, which were widespread in the Upper Triassic marine basin of Central Europe, the deposits of which in Germany are known as shell limestone.
By the end of the Triassic, most ancient groups of ammonites died out, but representatives of the Phylloceratida survived in Tethys, the giant Mesozoic Mediterranean Sea. This group developed so rapidly in the Jurassic that the ammonites of this time surpassed the Triassic in the variety of forms. During the Cretaceous, cephalopods, both ammonites and belemnites, remained numerous, but during the Late Cretaceous the number of species in both groups began to decline. Among the ammonites at this time, aberrant forms with an incompletely twisted hook-shaped shell (Scaphites), with a shell elongated in a straight line (Baculites) and with an irregularly shaped shell (Heteroceras) appeared. These aberrant forms appeared, apparently, as a result of changes in the course of individual development and narrow specialization. The terminal Upper Cretaceous forms of some branches of ammonites are distinguished by sharply increased shell sizes. In the genus Parapachydiscus, for example, the shell diameter reaches 2.5 m.
The mentioned belemnites also acquired great importance in the Mesozoic. Some of their genera, for example, Actinocamax and Belenmitella, are important fossils and are successfully used for stratigraphic division and accurate determination of the age of marine sediments.
At the end of the Mesozoic, all ammonites and belemnites became extinct. Of the cephalopods with an external shell, only the genus Nautilus has survived to this day. More widespread in modern seas are forms with internal shells - octopuses, cuttlefish and squids, distantly related to belemnites.
The Mesozoic era was a time of unstoppable expansion of vertebrates. Of the Paleozoic fishes, only a few transitioned into the Mesozoic, as did the genus Xenacanthus, the last representative of the freshwater sharks of the Paleozoic, known from freshwater sediments of the Australian Triassic. Sea sharks continued to evolve throughout the Mesozoic; Most modern genera were already represented in the Cretaceous seas, in particular, Carcharias, Carcharodon, lsurus, etc.
Ray-finned fish, which arose at the end of the Silurian, initially lived only in freshwater reservoirs, but with the Permian they began to enter the seas, where they multiplied unusually and from the Triassic to the present day they retained a dominant position.
Reptiles became most widespread in the Mesozoic, becoming truly the dominant class of this era. In the course of evolution, a variety of genera and species of reptiles appeared, often of very impressive size. Among them were the largest and most bizarre land animals the earth has ever bore. As already mentioned, in terms of anatomical structure, the most ancient reptiles were close to labyrinthodonts. The oldest and most primitive reptiles were the clumsy cotylosaurs (Cotylosauria), which appeared already at the beginning of the Middle Carboniferous and became extinct by the end of the Triassic. Among cotylosaurs, both small animal-eating and relatively large herbivorous forms (pareiasaurs) are known. The descendants of cotylosaurs gave rise to the entire diversity of the reptile world. One of the most interesting groups of reptiles that developed from cotylosaurs were the beast-like animals (Synapsida, or Theromorpha), their primitive representatives (pelycosaurs) have been known since the end of the Middle Carboniferous. In the mid-Permian period, pelycosaurs, known mainly from North America, are dying out, but in the Old World they are replaced by more progressive forms that form the order Therapsida.
The predatory theriodonts (Theriodontia) included in it are already very similar to primitive mammals, and it is no coincidence - it was from them that the first mammals developed by the end of the Triassic.
During the Triassic period, many new groups of reptiles appeared. These include turtles, ichthyosaurs ("fish lizards"), well adapted to marine life, resembling dolphins in appearance, and placodonts, clumsy armored animals with powerful flattened teeth adapted for crushing shells, and also plesiosaurs that lived in the seas, having a relatively small head, more or a less elongated neck, a wide body, flipper-like paired limbs and a short tail; Plesiosaurs vaguely resemble giant shellless turtles. In the Jurassic, plesiosaurs, like ichthyosaurs, reached their peak. Both of these groups remained very numerous into the Early Cretaceous, being extremely characteristic predators of the Mesozoic seas.
From an evolutionary point of view, one of the most important groups of Mesozoic reptiles were thecodonts, small predatory reptiles of the Triassic period, which gave rise to the most diverse groups - crocodiles, dinosaurs, flying lizards, and, finally, birds.
However, the most remarkable group of Mesozoic reptiles were the well-known dinosaurs. They developed from thecodonts back in the Triassic and took a dominant position on Earth in the Jurassic and Cretaceous. Dinosaurs are represented by two groups, completely separate - saurischia (Saurischia) and ornithischia (Ornithischia). In the Jurassic, real monsters could be found among dinosaurs, up to 25-30 m long (including tail) and weighing up to 50 tons. Of these giants, the best known forms are Brontosaurus, Diplodocus and Brachiosaurus. And in the Cretaceous period the evolutionary progress of dinosaurs continued. Among the European dinosaurs of this time, bipedal iguanodonts are widely known; in America, four-legged horned dinosaurs (Triceratops) Styracosaurus, etc.), somewhat reminiscent of modern rhinoceroses, became widespread. Also interesting are the relatively small armored dinosaurs (Ankylosauria), covered with a massive bony shell. All named forms were herbivores, as well as giant duck-billed dinosaurs (Anatosaurus, Trachodon, etc.), which walked on two legs. In the Cretaceous, predatory dinosaurs also flourished, the most remarkable of which were such forms as Tyrannosaurus rex, whose length exceeded 15 m, Gorgosaurus and Tarbosaurus. All of these forms, which turned out to be the greatest land predatory animals in the entire history of the Earth, walked on two legs.
At the end of the Triassic, the thecodonts also gave rise to the first crocodiles, which became abundant only in the Jurassic period (Steneosaurus and others). In the Jurassic period, flying lizards appeared - pterosaurs (Pterosauria), also descended from thecodonts.
Among the flying dinosaurs of the Jurassic, the most famous are Rhamphorhynchus and Pterodactylus; among the Cretaceous forms, the most interesting is the relatively very large Pteranodon. Flying lizards became extinct by the end of the Cretaceous.
In the Cretaceous seas, giant predatory mosasaurian lizards, exceeding 10 m in length, became widespread. Among modern lizards, they are closest to monitor lizards, but differ from them, in particular, in their flipper-like limbs. By the end of the Cretaceous, the first snakes (Ophidia) appeared, apparently descended from lizards that led a burrowing lifestyle.
Towards the end of the Cretaceous, there was a mass extinction of characteristic Mesozoic groups of reptiles, including dinosaurs, ichthyosaurs, plesiosaurs, pterosaurs and mosasaurs.
Representatives of the class of birds (Aves) first appear in Jurassic deposits. The remains of Archaeopteryx, the well-known and so far only known first bird, were found in lithographic shales of the Upper Jurassic, near the Bavarian city of Solnhofen (Germany). During the Cretaceous period, the evolution of birds proceeded at a rapid pace; The characteristic genera of this time were Ichthyornis and Hesperornis, which still had serrated jaws.
The first mammals (Mattalia), modest animals no larger than a mouse, descended from animal-like reptiles in the Late Triassic. Throughout the Mesozoic they remained few in number and by the end of the era the original genera were largely extinct. The most ancient group of mammals were the triconodonts (Triconodonta), to which the most famous of the Triassic mammals, Morganucodon, belongs. Appears in the Jurassic
a number of new groups of mammals - Symmetrodonta, Docodonta, Multituberculata and Eupantotheria. Of all the named groups, only the Multituberculata survived the Mesozoic, the last representative of which died out in the Eocene. Polytuberculates were the most specialized of the Mesozoic mammals, convergently they had some similarities with rodents. The ancestors of the main groups of modern mammals - marsupials (Marsupialia) and placentals (Placentalia) were Eupantotheria. Both marsupials and placentals appeared in the Late Cretaceous. The most ancient group of placentals are insectivores (insectivora), which have survived to this day.
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.
It is not yet clear when the inherent pattern of reproduction and development of eggs in the air environment, characteristic of amniotes, took shape. 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.
The warm and humid climate of the Carboniferous was favorable for 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 - the 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 ( rich in glands skin, structure of limbs, etc.). Synapsids began a special line of reptilian development. Already in the Upper Carboniferous and Permian, various forms arose, 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 the 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 complex behavior have 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 include numerous groups that once dominated the world. 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 that were found on the territory of the former USSR (Kotlasia and others) made it possible for Soviet paleontologists to determine their 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. Its largest representatives 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, 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. 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, reminiscent of 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 the Eosuchia - namely the 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 “bipedality,” i.e. e. moving on the hind limbs alone. 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 has left its 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, we can trace step by step how a characteristic feature of crocodiles - the secondary palate - developed. 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 - saurischians and ornithischians, which arose completely independently from pseudosuchians. Their differences lie mainly in the structure of the hind limb girdle. Saurischia, whose kinship with pseudosuchia is beyond doubt, was originally only carnivorous. 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, reaching 5-9 m in height, ran on their hind legs alone and were deprived of a shell, but the first finger of their forelimbs was a bone spike that could serve as a good weapon of defense. 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, big eyes. The winged lizards apparently ate fish and probably lived along the coastal rocks, since, judging by the structure of the hind limbs, they could climb from flat surface they couldn't. 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, the earth's surface began to undergo such enormous mountain-building processes and associated climate changes 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.
Origin and diversity of ancient reptiles
Some representatives of this group of historical animals were the size of an ordinary cat. But the height of others can be compared with a five-story building.
Dinosaurs... Probably, this is one of the most interesting groups of animals in the entire history of the development of the Earth's fauna.
Origin of reptiles
The ancestors of reptiles are considered Batrachosaurus
- fossil animals found in Permian deposits. This group includes, for example, Seymouria
. These animals had characteristics intermediate between amphibians and reptiles. The outlines of their teeth and skull were typical of amphibians, and the structure of the spine and limbs was typical of reptiles. Seymouria spawned in the water, although she spent almost all her time on land. Her offspring developed into adults through the process of metamorphosis, which is typical of modern frogs. The limbs of Seymouria were more developed than those of early amphibians, and it easily moved along muddy soil, stepping on its five-toed paws. It ate insects, small animals, and sometimes even carrion. The fossilized contents of Seymouria's stomach indicate that it sometimes happened to eat its own kind.
The heyday of reptiles
The first reptiles evolved from Batrachosaurus cotylosaurs
- a group of reptiles that included reptiles that had a primitive skull structure.
Large cotylosaurs were herbivores and lived, like hippopotamuses, in swamps and river backwaters. Their heads had projections and ridges. They could probably bury themselves in the mud right up to their eyes. Fossil skeletons of these animals were discovered in Africa. Russian paleontologist Vladimir Prokhorovich Amalitsky was fascinated by the idea of finding African dinosaurs in Russia. After four years of research, he managed to find dozens of skeletons of these reptiles on the banks of the Northern Dvina.
From cotylosaurs during the Triassic period (during the Mesozoic era), many new groups of reptiles appeared. Turtles still retain a similar skull structure. All other orders of reptiles originate from cotylosaurs.
Beast-like lizards. At the end of the Permian period, a group of animal-like reptiles flourished. The skull of these animals was distinguished by one pair of lower temporal fossae. Among them were large four-legged forms (it is even difficult to call them “reptiles” in the exact meaning of the word). But there were also small forms. Some were predatory animals, others were herbivores. Predatory lizard Dimetrodon had powerful wedge-shaped teeth.
A characteristic feature of the animal is a leathery ridge, resembling a sail, starting from the spine. It was supported by long bony extensions extending from each vertebra. The sun warmed the blood circulating in the sail, and it transferred heat to the body. Possessing two types of teeth, Dimetrodon was a ferocious predator. The razor-sharp front teeth pierced the body of the victim, and the short and sharp back teeth were used for chewing food.
Among the lizards of this group, animals with teeth appeared for the first time different types: incisors, canines
And indigenous
. They were called beast-toothed. Predatory three-meter lizard inostranzevia
with fangs more than 10 cm long, it received its name in honor of the famous geologist Professor A. A. Inostrantsev. Predatory beast-toothed lizards ( theriodonts) are already very similar to primitive mammals, and it is no coincidence that it was from them that the first mammals developed by the end of the Triassic.
Dinosaurs- reptiles with two pairs of temporal pits in the skull. These animals, having appeared in the Triassic, received significant development in subsequent periods of the Mesozoic era (Jurassic and Cretaceous). Over 175 million years of development, these reptiles have given a huge variety of forms. Among them were both herbivorous and predatory, mobile and slow. Dinosaurs are divided into two squads: Lizard-pelvic And ornithischians.
Lizard-hipped dinosaurs walked on their hind legs. They were fast and agile predators. Tyrannosaurus
(1)
reached a length of 14 m and weighed about 4 tons. Small predatory dinosaurs - coelurosaurs
(2)
resembled birds. Some of them had a cover of hair-like feathers (and perhaps constant temperature body). The lizard-hatched dinosaurs also include the largest herbivorous dinosaurs - brachiosaurs(up to 50 tons), which had a small head on a long neck. 150 million years ago, a thirty-meter-long diplodocus- the largest animal ever known. To facilitate movement, these huge reptiles spent most of their time in water, that is, they led an amphibious lifestyle.
Ornithischian dinosaurs ate exclusively plant foods. Iguanodon also walked on two legs, its forelimbs were shortened. On the first toe of its forelimbs there was a large spike. Stegosaurus (4) had a small head and two rows of bony plates along the back. They served him as protection and carried out thermoregulation.
At the end of the Triassic, the first crocodiles arose from the descendants of cotilosaurs, which became widespread only in the Jurassic period. Then flying lizards appear - pterosaurs
, also originating from thecodonts. On their five-fingered forelimb, the last finger was able to make a special impression: very thick and equal in length... to the length of the animal’s body including the tail.
A leathery flight membrane was stretched between it and the hind limbs. Pterosaurs were numerous. Among them were species that were quite comparable in size to our ordinary birds. But there were also giants: with a wingspan of 7.5 m. Among the flying dinosaurs, the Jurassic is the most famous rhamphorhynchus (1) And pterodactyl (2) , of the Cretaceous forms the most interesting is relatively very large pteranodon. By the end of the Cretaceous, flying lizards became extinct.
Among the reptiles there were also aquatic lizards. Large fish-like ichthyosaurs
(1)
(8-12 m) with a spindle-shaped body, flipper-like limbs, and a fin-like tail - in general outline they resembled dolphins. Distinguished by an elongated neck plesiosaurs
(2)
probably inhabited the coastal seas. They ate fish and shellfish.
Interestingly, the remains of lizards very similar to modern ones were discovered in Mesozoic sediments.
In the Mesozoic era, which was distinguished by a particularly warm and even climate, primarily in the Jurassic period, reptiles reached their greatest prosperity. In those days, reptiles occupied the same high place in nature as mammals occupy in the modern fauna.
About 90 million years ago they began to die out. And 65-60 million years ago, only four modern orders remained from the former splendor of reptiles. Thus, the decline of reptiles continued for many millions of years. This was probably due to the deterioration of the climate, change of vegetation, and competition from animals of other groups that had such important advantages as a more developed brain and warm-bloodedness. Of the 16 orders of reptiles, only 4 have survived! About the rest, only one thing can be said: their adaptations were clearly not enough to meet the new circumstances. A striking example of the relativity of any device!
However, the heyday of reptiles was not in vain. After all, they were the necessary link for the emergence of new, more advanced classes of vertebrate animals. Mammals evolved from lizard-toothed dinosaurs, and birds evolved from saurian dinosaurs.
(Go through all pages of the lesson and complete all tasks)
Vertebrates began to populate land 370 million years ago. The first amphibians - Ichthyostegas - had many more signs of fish in their structure (which, by the way, is reflected in their name). Transitional forms from amphibians to reptiles were found in fossil remains. One of these forms is seymouria. From such forms came the first true reptiles - cotylosaurs, already more similar to lizards. The relationship of all these forms is established on the basis of the similarity of the skulls of these animals.
Cotylosaurs gave rise to 16 orders of reptiles known from the fossil record. The heyday of reptiles occurred in the Mesozoic era. To date, only four modern orders have remained from the former splendor of reptiles. But it would be wrong to assume that the extinction of reptiles occurred quickly (for example, due to some kind of catastrophe). It lasted for many millions of years. Mammals evolved from lizard-toothed dinosaurs, and birds evolved from saurian dinosaurs.
The meaning of reptiles. Most lizards and snakes, eating insects, rodents and terrestrial mollusks that harm agriculture, bring benefits to people. In some countries in South America, South Asia and Africa, non-venomous snakes are kept instead of cats. In nature, reptiles exist in common system food connections: some eat plants, others eat animals (insects, amphibians, reptiles, small animals), and they, in turn, are eaten by other predators - birds of prey and animals.
Sometimes land turtles cause damage to melon fields, and water snakes cause damage to fish farms. Reptiles can spread pathogens to humans and domestic animals.
The bites of poisonous snakes are dangerous. However, studying the effect of snake venoms has made it possible to create valuable medicinal preparations based on them, which are used in the treatment of diseases of the respiratory organs, heart, and joints.
Large snakes and crocodiles are hunted for beautiful and durable leather. Sea turtles are hunted for their tasty meat. Due to overfishing, the numbers of many species have sharply decreased, some are on the verge of extinction. Nature reserves have been created for them. The elephant tortoise is listed in the WSOP Red Book, green turtle, Komodo dragon, Cuban crocodile, gattperia.
Among reptiles there are herbivorous and insectivorous species. Most are predators. By eating plants, insects, amphibians, and small animals, reptiles regulate their numbers.
Modern reptiles descended from ancient amphibians - stegocephalians, who lived about 350-400 million years ago. Cotylosaurs, which existed 230-250 million years ago, are considered the most ancient of reptiles. Some features of their organization have been preserved in turtles.
The heyday of reptiles was the period from 250 to 65 million years ago. In those days, numerous reptiles lived on land and in water, and moved in the air (Fig. 153).
Rice. 153. Ancient reptiles: 1 - diplodocus; 2 - pteranodon; 3 - ceratosaurus; 4 - ichthyosaur
Flying lizards - pterodactyls, rhamphorhynchus, pteranodons - looked like giant bats. Their wingspan reached 10-12 m. Lizards resembling dolphins and seals lived in the water - ichthyosaurs, plesiosaurs. These groups of ancient reptiles became extinct, leaving no descendants behind.
Among the ancient lizards there were two more groups that played an important role in the emergence of birds and mammals: dinosaurs and beast-like reptiles (Fig. 154).
Rice. 154. Animal-like beast-toothed reptile
Dinosaurs were a very diverse group: peaceful (herbivorous) and ferocious predators. Some walked on four legs, others only on two hind legs, in an upright position. Very large dinosaurs are known - more than 30 m long, and small ones - the size of a small lizard. Diplodocus (27 m long and weighing about 10 tons), Apatosaurus, Brachiosaurus, and Seismosaurus are also considered the largest. They lived near bodies of water and stood in the water for a long time, eating aquatic and semi-aquatic vegetation. Some dinosaurs had ridges on their backs that they used to catch solar energy. Scientists suggest that birds originated from one of the groups of dinosaurs.
Beast-like reptiles got their name for their resemblance to animals. So, unlike other lizards, their legs were not widely spaced: they were located under the body, and not on the sides. The teeth were divided (differentiated) into incisors, canines and molars. They had fleshy lips, and their skin probably contained glands.
For 200 million years, the fate of dinosaurs and beast-like reptiles was different. Dinosaurs were favored by the warm, mild climate of that era, and they dominated everywhere. The beast-like creatures were few in number and invisible. Approximately 120-130 million years ago, the ratio of the number of species began to change in favor of animal-like ones.
The extinction of dinosaurs occurred as the planet's climate changed. About 130 million years ago, a long warm period was replaced by cooling. The vegetation began to change: angiosperms gradually spread.
There are many scientifically based hypotheses about the causes of the extinction of dinosaurs, for example, active mountain building and associated climate change. Perhaps a large asteroid passed near the Earth, influencing the climate and the natural environment surrounding dinosaurs.
Did the ancient lizards disappear from the face of the planet without a trace, leaving only monuments in the form of skeletons and prints? In the modern fauna of reptiles there is a hatteria, which is called a living fossil. The appearance of this animal has many ancient features: the remains of a shell on the body, the primitive structure of the spine, and an additional parietal eye. This reptile lives on small islands off New Zealand and is strictly protected as a “living natural monument.” Turtles are close to their Mesozoic ancestors. In some organizational features, crocodiles are close to dinosaurs.
Lizards and snakes also have some similarities with dinosaurs. But if lizards are a fairly ancient group, then snakes appeared only at the end of the warm period on Earth before the cold snap, when their related groups lost their former greatness.
Reptiles descended from ancient amphibians - stegocephalians. The most ancient reptiles are cotylosaurs. A variety of ancient reptiles inhabited land, aquatic environments, and lived in the air and flourished for 200 million years. Modern reptiles, birds and mammals evolved from ancient reptiles.
Representatives of reptiles (more than 4 thousand species) are true terrestrial vertebrates. Due to the appearance of the embryonic membranes, they are not associated with water in their development. As a result of the progressive development of the lungs, adult forms can live on land in any conditions. Reptiles living in the species are secondary aquatic, i.e. their ancestors switched from a terrestrial lifestyle to an aquatic one.
Remember! Reptiles and reptiles are the same class!
Reptiles, or reptiles, appeared at the end of the Carboniferous period, approximately 200 million years BC. when the climate became dry, and in some places even hot. This created favorable conditions for the development of reptiles, which turned out to be more adapted to living on land than amphibians. A number of traits contributed to the advantage of reptiles in competition with amphibians and their biological progress. These include:
The development of horny scales on the surface of the body, protecting against adverse environmental influences, primarily from the drying effects of air, was also important. The prerequisite for the appearance of this device was liberation from skin respiration due to the progressive development of the lungs.
A typical representative of reptiles is the sand lizard. Its length is 15-20cm. It has a well-defined protective coloration: greenish-brown or brown, depending on its habitat. During the day, lizards are easy to see in a sun-warmed area. At night they crawl under stones, into holes and other shelters. They spend the winter in the same shelters. Their food is insects.
On the territory of the CIS, the most widespread are: in the forest zone - the viviparous lizard, in the steppe - the sand lizard. The spindle is a lizard. It reaches 30-40 cm, has no legs, which reminds it of a snake, this often costs it its life. The skin of reptiles is always dry, devoid of glands, and covered with horny scales, scutes or plates.
Skeleton. The spinal column is already divided into cervical, thoracic, lumbar, sacral and caudal sections. The skull is bony, the head is very mobile. The limbs end in five fingers with claws.
The muscles of reptiles are much better developed than those of amphibians.
Digestive system . The mouth leads into the oral cavity, equipped with a tongue and teeth, but the teeth are still primitive, of the same type, and serve only to capture and hold prey. The alimentary canal consists of the esophagus, stomach, and intestines. At the border of the large and small intestines the rudiment of the cecum is located. The intestines end in a cloaca. Digestive glands are developed: pancreas and liver.
Respiratory system. The respiratory tract is much more differentiated than in amphibians. There is a long trachea that branches into two bronchi. The bronchi enter the lungs, which look like cellular, thin-walled sacs, with big amount internal partitions. The increase in the respiratory surfaces of the lungs in reptiles is associated with the lack of cutaneous respiration.
Excretory system represented by the kidneys and ureters flowing into the cloaca. The bladder also opens into it.
Circulatory system. Reptiles have two circles of blood circulation, but they are not completely separated from each other, due to which the blood is partially mixed. The heart has three chambers, but the ventricle is divided by an incomplete septum.
Crocodiles already have a real four-chambered heart. The right half of the ventricle is venous, and the left part is arterial - the right aortic arch originates from it. Converging under the spinal column, they unite into the unpaired dorsal aorta.
The brain of reptiles differs from the brain of amphibians in the greater development of the hemispheres and cerebral vault, as well as the separation of the parietal lobes. Appears for the first time, the cerebral cortex. 12 pairs of cranial nerves arise from the brain. The cerebellum is somewhat more developed than in amphibians, which is associated with more complex coordination of movements.
At the front end of the lizard's head there is a pair of nostrils. The sense of smell in reptiles is better developed than in amphibians.
The eyes have eyelids, upper and lower, in addition, there is a third eyelid - a translucent nictitating membrane that constantly moisturizes the surface of the eye. Behind the eyes is a rounded eardrum. Hearing is well developed. The organ of touch is the tip of the forked tongue, which the lizard constantly sticks out of its mouth.
Unlike fish and amphibians, which have external fertilization (in water), reptiles, like all non-amphibious animals, have internal fertilization, in the body of the female. The eggs are surrounded by embryonic membranes that enable development on land.
The female lizard quickly lays 5-15 eggs in a secluded place at the beginning of summer. The eggs contain nutritional material for the developing embryo and are surrounded on the outside by a leathery shell. A young lizard emerges from the egg, looking like an adult. Some reptiles, including some species of lizards, are ovoviviparous (i.e., a baby immediately emerges from a laid egg).
Many species of lizards, when grabbed by the tail, break it off with sharp lateral movements. Throwing back the tail is a reflex response to pain. This should be considered as an adaptation thanks to which lizards escape from enemies. A new one grows in place of the lost tail.
Modern reptiles are divided into four orders:
Protolizards represented by a single type - tuateria, which is one of the most primitive reptiles. The tuateria lives on the islands of New Zealand.
Scaly animals include lizards, chameleons and snakes. This is the only relatively numerous group of reptiles - about 4 thousand species.
Lizards are characterized by well-developed five-fingered limbs, movable eyelids and the presence of an eardrum. This order includes agamas, poisonous lizards, monitor lizards, true lizards, etc. Most species of lizards are found in the tropics.
Snakes are adapted to crawling on their belly. Their neck is not pronounced, so the body is divided into head, torso and tail. The spinal column, which contains up to 400 vertebrae, is highly flexible thanks to additional articulations. The belts, limbs and sternum are atrophied. Only some snakes have preserved a rudimentary pelvis.
Many snakes have two poisonous teeth on their upper jaws. The tooth has a longitudinal groove or duct through which the poison flows into the wound when bitten. The tympanic cavity and membrane are atrophied. The eyes are hidden under transparent skin, without eyelids. The snake's skin becomes keratinized on the surface and is periodically shed, i.e. moulting occurs.
Snakes have the ability to open their mouths very wide and swallow their prey whole. This is achieved by the fact that a number of skull bones are connected movably, and the lower jaws in front are connected by a very tensile ligament.
The most common snakes in the CIS are snakes, copperheads, snakes. The steppe viper is listed in the Red Book. For its habitat, it avoids agricultural lands, but lives on virgin lands, which are becoming less and less, which threatens it with extinction. The steppe viper (like other snakes) feeds mainly on mouse-like rodents, which is certainly useful. Its bite is poisonous, but not fatal. She can attack a person only by accident, being disturbed by him.
The bites of poisonous snakes - cobra, epha, viper, rattlesnake and others - can be fatal to humans. Of the fauna, the gray cobra and sand epha, which are found in Central Asia, as well as the viper, found in Central Asia and Transcaucasia, the Armenian viper, living in Transcaucasia. The bites of the common viper and copperhead are very painful, but usually not fatal to humans.
The science that studies reptiles is called herpetology.
Recently, snake venom has been used in medicinal purposes. Snake venom is used for various bleedings as a hemostatic agent. It turned out that some drugs obtained from snake venom reduce pain due to rheumatism and diseases nervous system. To obtain snake venom for the purpose of studying the biology of snakes, they are kept in special nurseries.
Crocodiles are the most highly organized reptiles, having a four-chambered heart. However, the structure of the partitions in it is such that venous and arterial blood are partially mixed.
Crocodiles are adapted to an aquatic lifestyle, and therefore have swimming membranes between the toes, valves that close the ears and nostrils, and a velum that closes the pharynx. Crocodiles live in fresh waters, come to land to sleep and lay eggs.
Turtles are covered above and below with a dense shell with horny scutes. Their chest is motionless, so their limbs take part in the act of breathing - when they are drawn in, the air leaves the lungs, when they stick out, it enters them. Several species of turtles live in Russia. Some species are eaten, including the Turkestan tortoise, which lives in Central Asia.
It has been established that in the distant past (hundreds of millions of years ago) various types of reptiles were extremely common on Earth. They inhabited land, water, and less often air. Most species of reptiles became extinct due to climate change (cold temperatures) and the rise of birds and mammals, with which they could not compete. Extinct reptiles include orders of dinosaurs, wild-toothed lizards, ichthyosaurs, flying lizards, etc.
This is the most diverse and numerous group of reptiles that has ever lived on Earth. Among them were both small animals (the size of a cat and smaller) and giants, whose length reached almost 30 m and weight - 40-50 tons.
Large animals had a small head, a long neck and a powerful tail. Some dinosaurs were herbivores, others were carnivores. The skin either had no scales or was covered with a bone shell. Many dinosaurs ran galloping on their hind limbs, leaning on their tail, while others moved on all four legs.
Among the ancient land reptiles there were representatives of a progressive group, which resembled animals in the structure of their teeth. Their teeth were differentiated into incisors, canines and molars. The evolution of these animals went in the direction of strengthening their limbs and belts. In the process of evolution, mammals arose from them.
Fossil reptiles are of great importance because they once dominated the globe and from them came not only modern reptiles, but also birds and mammals.
Living conditions at the end of the Paleozoic changed dramatically. Instead of a warm and humid climate, cold winters appeared and a dry and hot climate established. These conditions were unfavorable for the existence of amphibians. However, under such conditions, reptiles began to develop, whose skin was protected from evaporation, a terrestrial method of reproduction, a relatively highly developed brain and other progressive characteristics appeared, which are given in the characteristics of the class.
Based on a study of the structure of amphibians and reptiles, scientists came to the conclusion that there are great similarities between them. This was especially true for ancient reptiles and stegocephalians.
All this suggests that reptiles evolved from amphibians.
