What ancient animals are considered the ancestors of birds? Dinosaurs are birds. The origin of birds from dinosaurs has been refuted

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“And why don’t people fly like... dinosaurs?” ©

For the first time, the thought of the giant-toothed origin of sparrows, ducks, geese and other feathered creatures came to me on Sunday morning - some stomping creature was jumping along the galvanized tide outside the window, commenting on its jumps with screams at high notes. Having slightly pulled back the curtain, I discovered a bird of the starling system - and it was at that moment that the starling for some reason reminded me of the tyrannosaurus, popular among filmmakers. Yes, damn it - the same turns of the head, swaying of the body when walking, unpleasant shouts! Is it really possible that among the ancestors of chilled chicken carcasses sold in retail networks, were there dinosaurs?

Tyrannosaurus is a close relative of the hummingbird

The first thing that birds have in common with dinosaurs is the eggs that they carried for the purpose of procreation. However, the only group of less well-known flying dinosaurs is the pterodactyls, which, judging by the images reconstructed by paleontologists, had no plumage at all... And one more thing - it is well known that any reptiles are cold-blooded, i.e. their bodies are not able to maintain a constant temperature like mammals. And all birds are warm-blooded.

According to school course In biology, the ancestor of modern birds is considered to be Archeopteryx - this creature really looked like a bird with its plumage and the structure of some bones. But according to the results of research in recent decades, Archeopteryx was not a bird; to a greater extent This is a subspecies of dinosaurs, and a dead-end one at that, i.e. not received further development and completely went extinct millions of years ago. So who is he - the ancestor of birds?

Paleontologists believe that birds evolved from therapods - predatory dinosaurs with strong and long legs, short upper legs, a strong skull, sharp teeth and an excellent appetite. The structure of the bird skeleton and the skeletons of dinosaurs of two families from the subclass of therapods - oviraptosaurs and dromaeosaurids - is very similar. Moreover, representatives of several dinosaur genera belonging to the mentioned families were covered with feathers and had wings!

66 million years ago, at the very end of the Cretaceous period, there lived dromaeosaurids. Strong, agile, about 180 cm tall and weighing about 15 kg, the dromaeosaur was a successful hunter of live prey - its long legs allowed it to accelerate to 80 km/h and jump up to 7 m. Each leg had a long and sharp claw, with with the help of which the dromaeosaur pierced the skin of the victim in a jump, and also climbed trees to hunt from ambush. The short wings did not allow it to fly - the dinosaur used them to brake when turning. If you do not take into account the long tail and toothy mouth of the lizard, then in its size the dromaeosaur was similar to modern ostriches.

In the family of oviraptosaurs, paleontologists discovered the largest representative of bird-dinosaurs in the history of the Earth, which had wings - Gigantoraptor, whose height exceeded 3 meters, and the total length of the body including the tail was about 8 meters. The weight of this dinosaur bird is one and a half to two tons. The interesting things don’t end there - Gigantoraptor did not have the toothy mouth characteristic of dinosaurs, it had... a bird’s beak! Like dromaeosaurs, Gigantoraptor used short wings to slow down turns while chasing prey.

By the way, the largest dinosaur from the therapod suborder, although it did not have wings, but was covered with the simplest 15-centimeter feathers, was Yutyrannus - a height of 3.5 meters, a body length of 9 meters and a weight of one and a half tons. Yutyrannus lived at the beginning of the Cretaceous period, about 125 million years ago and belonged to the family of tyrannosaurs - yes, those same tyrannosaurs!

Let's return to the oviraptosaurs, erroneously called "egg stealers" by scientists, because... paleontologists of the last century considered them as such. In fact, the two-meter and 400-kilogram oviraptors, who lived 75 million years ago, did not steal other people’s eggs at all; on the contrary, they incubated their clutches, as modern birds do. Oviraptosaurs could not fly, their wings were too short, but the body of these dinosaurs was completely covered with feathers, and the head was equipped with a bird's beak.

In conclusion, I present to you Avimimus, a small representative of the oviraptosaur family - height no more than 70 centimeters, weight about 15 kg. This dinosaur could not fly due to the same short wings, but it ran well, its beak was equipped with teeth, which allows scientists to consider Avimim as a carnivore. But look at his image again - who does he look more like, a dinosaur or... for example, a secretary bird?

The Cretaceous era gave birth not only to feathered dinosaurs, but also to the first birds - Protoavis, Ichthyornis, Enantiornis, etc., which feathered dinosaurs happily fed on. As you know, the Cretaceous period ended with a sharp drop in temperature on our planet, which is why all representatives of the dinosaurs died out, but the first birds survived - developed plumage and divided blood circulation (arterial and venous) allowed them to maintain body temperature regardless of solar heat. And the wings made it easier to move from food-poor areas to rich ones, from cold to warm ones. Feathered land dinosaurs also tried to insulate their bodies with feathers, but either they evolved too slowly, or their modernization stopped there - nevertheless, it was the era of dinosaurs that gave birth to modern birds.

The hunt for the ancestors of living birds began with the discovery of Archeopteryx, the first known bird discovered in the early 1860s. Like birds, it had feathers along its front legs and tail, but unlike modern birds, it also had teeth and a long, bony tail. Additionally, many of the bones in Archeopteryx's arms, shoulder girdles, pelvis, and legs were separated and did not fuse or shrink as they do in modern birds. Based on these characteristics, Archaeopteryx was recognized as an intermediate between birds and reptiles.

In the 1970s, paleontologists noticed that Archeopteryx shared unique features with small carnivorous dinosaurs called theropods. All dinosaur groups in this eugram, except the ornithischian dinosaurs, are theropods. Based on these similarities, scientists have suggested that theropods may have been the ancestors of birds. When paleontologists began constructing an evolutionary tree to study the question, they became even more convinced of this. Birds are just a branch coming from the dinosaur branch on the tree of life.

As birds evolved from theropod dinosaurs, many of their features were modified. However, it is important to remember that the animals were not "trying" to be birds in any sense. In fact, the closer we look, the more obvious it is that the set of features that characterize birds evolved through a complex series of steps and served different functions along the way.

After Archeopteryx appeared on the scene, birds continued to evolve in the same directions as their theropod ancestors. In many species, the bones were greatly reduced and “fused together,” which may have helped improve flight efficiency. Likewise, the bone walls became even thinner, and the feathers became longer and their blades asymmetrical, probably in this way they further improved their aerodynamic abilities. The bones in the tail almost completely disappeared, being replaced by a tuft of tail feathers and eventually taking on the function of improving stability and agility. The pectoral keel, which was present in non-pid dinosaurs, became stronger and more complex in structure, and the bones of the shoulder girdle developed and connected to the chest, securing the flight apparatus of the forelimbs. The breast bone itself became larger and developed a central keel along the midline of the chest, to which the muscles that control flight were attached. The front legs evolved to become longer than the legs as the primary form of locomotion switched from running to flying, and teeth disappeared in early birds. The ancestor of all modern birds lived sometime during the late Cretaceous period, and in the 65 million years since the extinction of the remaining dinosaurs, this branch has grown into the main groups of birds living today.

Many scientists believe that birds evolved from small theropod dinosaurs. The main thing here was the appearance of feathers = as a result, some running and climbing animals gained the ability to fly.
Scientists consider Archeopteryx, first discovered in 1861, to be the first bird itself. Judging by its appearance, it looked like a cross between a reptile and a bird, with a toothy beak, a long bony tail and distinct plumage. IN recent years remains of other feathered reptiles were also found.

The very first feathered birds.

Bird plumage performs two important functions: warms birds and helps them fly. Those feathers that serve for heating are usually shorter and softer, and those with which birds fly - the so-called flight feathers - are larger and curved in the shape of a fan. It is unlikely that the plumage of both species appeared in birds at the same time. They were almost certainly the first to grow heat-protective feathers, and then, millions of years later, some of them acquired a different, completely special form, designed specifically for flight. When exactly the plumage appeared is unknown. According to some paleontologists, some semblance of feathers is already found in a reptile that lived in Russia, however, most scientists are not completely convinced of this. The most convincing evidence in this sense comes from the presence of plumage as such in small theropods, whose fossilized remains were recently discovered in China. One of them, Sinosauropteryx, preserved obvious signs short fluffy plumage in the form of a long comb stretching along the neck and entire back. It was already a feathered dinosaur, but it quite obviously did not yet know how to fly.

Taking off from the ground.

Sinosauropteryxes appeared somewhat later than Archeopteryxes, which makes it clear that the former were not their direct descendants. Meanwhile, judging by the presence of fluffy plumage in the ancestors of flying birds, it is easy to imagine what they looked like long before full plumage. But what is much more important is not even this, but how the wings developed and, most importantly, why? According to one theory, wings developed among the ancestors of today's birds as a special adaptation for hunting insects and other small animals. So, according to this very theory, the first birds, trying to overtake the victim, took off from the ground and overtook it in a jump, already in the air. Then, following the same theory, a long time later, the front legs of the first birds began to grow feathers, which helped them maintain balance or, perhaps, hold prey. The feathers gradually stretched out, and the muscles on the front legs became stronger. This is probably how animals arose that one fine day had the strength to get off the ground.

Avimim (left) was a feathered theropod, but it could not fly. Archeopteryx (center) was smaller and lighter, and also had well-developed flight feathers. Compared to Archeopteryx, modern birds like the pigeon (right) have no teeth or claws on their wings, with the possible exception of the gaocin, and their tails are noticeably shorter.

Tree flying squirrels.

This "down-to-earth theory" was based on some characteristic features, identified in Archeopteryx, for example, the extraordinary strength of the paws. However, according to most paleontologists, modern birds descended from reptiles that lived not on land, but in trees. With the development of exceptionally long feathers, such animals gained the ability to float in the air, which allowed them to easily move through wooded areas without descending to the ground. Well, over time, they learned to fly for real - by flapping their wings. But it took the reptiles a lot of time to get the hang of soaring. This was achieved, for example, by coelurosaurus and other arboreal reptiles; the same can be said about some modern lizards. And supporters of the “tree” theory consider this direct evidence that the first birds started from the same thing.
Archeopteryx had asymmetrical, or rather curved, feathers on its wings, like modern birds. Feathers like these help birds fly when the wind blows over them, which in turn confirms that Archeopteryx could fly.

Weight and flight.

It doesn’t take much strength to soar, but flapping your wings is not an easy task. Over time, serious changes occurred in the anatomy of the first birds, thanks to which they learned not only to stay in the air for a long time, but also began to differ strikingly from their ancestors - dinosaurs. In this sense, evolution took a completely different path. And as they developed, the first birds began to spend more and more time in the air. Thanks to the same changes, the birds got rid of excess weight. The bones of the first birds were mostly fused, due to which their skeleton was slightly lighter. Like their theropod ancestors, the bones of the first birds were hollow, filled with air - over time, the air cavities expanded, especially towards the wings and paws. In addition, their sternum expanded and became stronger. pectoral muscles, which ensured flight, as well as a triangular fork, or arch, that supported the sternum during flight. Such anatomical changes turned out to be quite successful. In the Cretaceous period, birds literally filled the Earth, especially since the time of reptiles was nearing its fatal end. Therefore, birds were the only surviving descendants of dinosaurs.

Archeopteryx closely resembled a small theropod. Archaeopteryx fossils found in the 1950s were thought to belong to Compsognathus until the faint outline of feathers was discovered next to them.

Similarities between birds and reptiles
It is easy to see the similarities between the classes of birds and reptiles. In both, the skin is almost devoid of glands, but is protected by horny scales in reptiles and feathers in birds. Note that in birds scales are developed on the non-feathered parts of the skin (tarsus). Bird feathers are also horny structures that develop from scales. Both classes are oviparous, and eggs are arranged in a similar way: shell, yolk and white. The embryos of birds and reptiles are similar in appearance.

The ancestors of birds are ancient reptiles

In the search for immediate reptilian ancestors, small primitive reptiles were selected pseudosuchia, who lived approximately 200 million years ago (Triassic period). In search of food, some of these creatures adapted to climbing trees and jumping from branch to branch. In the course of evolution, this method turned out to be promising and helped primitive birds avoid competition among related species and escape from predators. As the scales lengthened, they turned into feathers, which helped the ancient ancestors of birds acquire the ability to plan, and then to be active, i.e. flapping, flight, which most modern birds have.

The oldest bird

Protoavia (1984) was found in Post, Texas, USA, with an estimated age of 225,000,000 years.

The first birds appeared in the Mesozoic era

The development of the Earth is divided into five periods of time called eras. The first two eras, Archeozoic and Proterozoic, lasted 4 billion years, that is, almost 80% of all earthly history. During the Archeozoic, the formation of the Earth occurred, water and oxygen appeared. About 3.5 billion years ago, the first tiny bacteria and algae appeared. During the Proterozoic era, about 700 years ago, the first animals appeared in the sea. These were primitive invertebrate creatures, such as worms and jellyfish. The Paleozoic era began 590 million years ago and lasted 342 million years. Then the Earth was covered with swamps. During the Paleozoic, large plants, fish and amphibians appeared. The Mesozoic era began 248 million years ago and lasted 183 million years. At this time, the Earth was inhabited by huge dinosaur lizards. The first mammals and birds also appeared. The Cenozoic era began 65 million years ago and continues to this day. At this time, the plants and animals that surround us today arose.

Descended from coelurosaurs

Living at the end of the Triassic and in the Jurassic period, small carnivorous dinosaurs from the group coelurosaurs were bipedal from long tails and small forelimbs of the grasping type. They did not need to climb trees and glide from branch to branch. The active flight of ancient birds could have arisen on the basis of the flapping movements of the forelimbs, which helped knock down flying insects, for which, by the way, predators had to jump high. Coelurosaurs survived mass extinction dinosaurs at the end Mesozoic era.

The very first dinosaur birds
In the Mesozoic era, that is, 150 million years ago, the ancestors of birds constituted the main group of land animals in Argentina. They are called theropods (Argentavis magnificens), beast-footed lizards, and they already knew how to fly. Therapods moved on two legs, their front legs turned into short grasping limbs. It was no longer possible to rely on them, but it was convenient to fight with prey. The powerful jaws of theropods were densely lined with teeth and resembled a saw blade. In place of worn-down teeth, new ones grew, so even when they grew old, the lizards could still torment their prey with the same fervor. (Sharks also renew their teeth.) During the process of evolution, some theropods developed a horny beak. Analyzing the anatomical features of theropods, it is believed that birds originated from these animals.

Fossils found in Argentina in 1979 indicate that this huge vulture-like bird had a wingspan of more than 6 m, a height of 7.6 m, and a weight of 80 kg.

Beast-like predatory lizard ornitholestes, which had a body length of 2.5 m, gives an idea of ​​ancient birds.

their wingspan was 7.5 m; they lived in Europe, Africa, North and South America and were carnivores (eating fish and aquatic invertebrates).

Modern bird that lived 120 million years ago

After studying the fossilized remains of a small bird found in Liaoning province in northern China, scientists came to the conclusion that "Confuciusornis sanctus" - as the ancient bird was dubbed - lived 120 million years ago. Judging by the structure of the beak, Confuciusornis resembled modern birds: the teeth were no longer there, but a horny sheath had appeared.

The appearance of flapping flight

In the Jurassic period, birds acquired the ability to actively fly. Thanks to the swings of their forelimbs, they were able to overcome the effects of gravity and gained many advantages over their ground-based, climbing and gliding competitors. Flight allowed them to catch insects in the air, effectively avoid predators and choose the most favorable environmental conditions for life. Its development was accompanied by a shortening of the long tail, replacing it with a fan of long feathers, well suited for steering and braking. Most of the anatomical transformations necessary for active flight were completed by the end of the Early Cretaceous (about 100 million years ago), i.e. long before the extinction of the dinosaurs.

There can be no talk of a direct relationship between lizards and birds.

Found by American scientists from North Carolina State University. They compared the changes in theropod limbs with the evolution of the wings of chickens, ostriches and cormorants. In the process of evolution, both of them retained only three fingers from the original five. However, American biologists have found that birds lack both external fingers, that is, the first and fifth. The lizards have lost their fourth and fifth fingers.

long bird
Skeleton of the lizard "unenlagia comahuensis", " long bird", found in May 1996 in Argentina, fills the gap separating the ancient theropod reptiles and the first bird, Archeopteryx.

Differences between birds and reptiles

The higher development of birds is evidenced by an enlarged brain (in particular, large sizes cerebral hemispheres and cerebellum in birds), perfection of respiratory and circulatory systems- double breathing and separation of arterial blood from venous blood, as well as constant body temperature. All these improvements in the organization of birds are absent in reptiles.

The oldest bird flew

The debate over whether Archeopteryx could fly has continued since 1861, when the first fossil was found, until now. The answer was found only recently. The creature's fossilized brain was placed in an X-ray machine, allowing thin "slices" of the object to be obtained. These slices were combined in a computer into a three-dimensional model. It turned out that in its anatomy the brain of Archeopteryx is much closer to the brain of modern flying birds than to the brain of dinosaurs, as paleontologists previously assumed. The analysis revealed, in particular, semicircular canals in the inner ear used for balance, and enlarged lobes of the brain responsible for vision - features that affect flight efficiency. The “flying” brain developed simultaneously with wings, and the ability to fly itself developed in the process of evolution much faster than scientists previously thought.

Bones served as conditioner

When hunting, ancient lizard-bird theropods regulated their body temperature to avoid overheating. The function of the air conditioner was performed by hollow bones.

Archeopteryx is the direct ancestor of modern birds

Remains of an extinct bird resembling a magpie that lived in the second half Jurassic period, i.e. 140 million years ago, were discovered in Europe. In the layers of the earth's crust, scientists discovered the fossilized bones of the skeleton of an unknown creature, and nearby the imprints of its feathers. The bird got a name archaeopteryx (Archaeopteryx litographica), What does "ancient bird" mean? This little bird had sharp teeth in cells, a long, lizard-like tail and forelimbs with three fingers bearing hooked claws.

Archeopteryx resembled a reptile

The shape of the Archeopteryx skull with teeth in both jaws and a very long tail with 20 vertebrae resembled a reptile. In most features, Archeopteryx was more like a reptile than a bird, except for the real feathers on the forelimbs and tail.

How did Archeopteryx fly?
The entire body of this creature, except the head, was covered with feathers, and the forelimbs had all the basic features of bird wings with flight feathers. Only the wing fingers were longer than those of modern birds and had claws. The feet had four toes: the first toe faced back, the rest - forward, which helped to grasp the branches well with the fingers. Tail feathers were attached in pairs on each vertebra of the long tail, and not, as in modern birds, in a wide fan on the coccygeal bone. Features of Arechaeopteryx indicate that it was capable of flapping flight, but only over very short distances.

An animal the size of a crow

Rahonavis This crow-sized animal, which lived about 80 million years ago, belongs to the same group of dinosaurs as Velociraptor. True, the creature also has a lot in common with birds. Rahonavis had a retractable sickle-shaped claw on its middle toe, feather cover, and a long, clawed tail similar to Archeopteryx.

The first birds lived in the forest

The first representatives of the class arose and began to master flight, living in the forest on tree branches, jumping and climbing branches, clinging to them with long fingers of the forelimbs with claws. Having spread their wings, they glided in the air from top to bottom along an inclined plane, and also flew short distances by flapping their wings. Only later did some birds begin to adapt to life in the steppes and deserts, on the banks of reservoirs and in other places.

Firstbird - another bird-dinosaur

Archeopteryx for a long time remained the only one known to science a connecting link between birds and reptiles, but in 1986 the remains of another fossil creature were found that lived 75 million years earlier and combined the characteristics of dinosaurs and birds. Although this animal was named Protoavis (protobird), its evolutionary significance is controversial among scientists.

Many bird species appeared during the Cretaceous period

After Archeopteryx, there is a gap of about 20 million years in the fossil record of birds. The following finds date back to the Cretaceous period, when many species of birds appeared, adapted to different habitats. Among the approximately two dozen Cretaceous taxa known from fossils, two are particularly interesting: Ichthyornis And Hesperornis. Both were opened in North America, in rocks, formed on the site of a vast inland sea.

Ichthyornis - an ancient gull

Ichthyornis was the same size as Archeopteryx, its body length was about 50 cm, and it weighed 5 kg. Outwardly, it resembled a seagull with well-developed wings, indicating the ability to fly powerfully. Like modern birds, it had no teeth, but its vertebrae were similar to those of a fish, hence its generic name, meaning “fish bird.” His remains were found in the USA. Ichthyornis lived 65-90 thousand years ago.

Hesperornis - an ancient loon

Hesperornis ("western bird") was 1.5–1.8 m long (up to 2 m) and almost wingless. His weight was 40 kg. With the help of huge flipper-like legs extending sideways at right angles at the very end of the body, it apparently swam and dived no worse than loons. It had teeth of a "reptilian" type, but the structure of the vertebrae was consistent with that typical of modern birds. The remains of Hesperornis were found in the USA. This bird lived 70 thousand years ago.

Modern birds formed 65 million years ago

With the onset of the Tertiary period (65 million years ago), the number of bird species began to increase rapidly. The oldest fossils of penguins, loons, cormorants, ducks, hawks, cranes, owls and some songbirds date back to this period.

Huge flightless birds
In addition to the ancestors of modern species, several huge flightless birds appeared in the Tertiary period, apparently occupying the ecological niche of large dinosaurs. One of them was Diatryma, discovered in Wyoming, 1.8–2.1 m tall, with massive legs, a powerful beak and very small, underdeveloped wings.

During the Cretaceous period there lived flying lizards or pterosaurs,

Their wingspan was 7.5 m; they lived in Europe, Africa, North and South America and were carnivores (eating fish and aquatic invertebrates).

Large prehistoric birds resembled ostriches

According to paleontological data, there were large, partially feathered lizards. In 1834, the French traveler Goudeau found half eggshells such a size that it could be used as a water dish. Then several giant bones were found in the swamps of the island, which were initially mistaken for the remains of an elephant or rhinoceros. But the bones belonged to a bird that must have weighed at least half a ton. Madagascar ostriches epiornithes (Aepyornithes), reached a height of 5 m, laid eggs 32 cm long and 22 cm wide, containing 8.5 liters of liquid contents. The largest egg in the Epyornis clutch is considered to be 24 cm long and 11 liters in volume.

Roc

The Venetian traveler Marco Polo did not have a chance to visit Madagascar himself, but he also heard amazing stories: “They say that there is a vulture bird there that appears in known time years, and in all respects the vulture is not what we think and how it is portrayed. They say that the vulture is half bird, half lion, and this is not true. Those who saw him claim that he looks like an eagle, but only very big... On the island they call him Ruk.”

Epiornis were ringed 5 thousand years ago

French zoologists discovered the remains of an apiornis in Madagascar with a bronze ring attached to the bird's leg. Experts came to the conclusion that the signs on the ring are nothing more than an impression of a seal from the era of the most ancient civilization in India - Mohenjo-Daro. made about five thousand years ago. Radiocarbon dating of the bird's bones helped establish its age: it is five thousand years old! In the 3rd millennium BC, the inhabitants of Hindustan made daring sea expeditions. By this time they had accumulated centuries of experience in driving ships, and the Indians had also visited Madagascar. At that time, apiornis were found here in abundance. In the stories of the sailors who returned home, they received a lot of attention.

Do aepornis still exist today?

The eggs, which were found on sand dunes and swamps in the southern part of the island of Madagascar, looked suspiciously fresh. They seemed to have been demolished quite recently. Local residents are sure that giant birds still live in the deepest forests of the island, but it is not easy to see them. In Madagascar, there are still huge areas of protected jungle and untrodden swamps; there is enough space for apyornis.

Ostrich dromomys from Australia

Judging by fossil leg bones found in 1974 near Alice Springs, flightless Dromomis stirtoni, a giant, ostrich-like bird that lived in central Australia from about 15 million to 25,000 years ago, reaching a height of 3 m and weighing about 500 kg.

Moa ostrich from New Zealand

A giant bird that looks like an ostrich moa (Dinornis maximus), inhabited the islands of New Zealand presumably until the beginning of the 19th century, probably still had greater growth- 3.7 m, and weighed about 230 kg.

When did Australia's last giant birds go extinct?

Analysis of ancient eggshells suggests Australia's enormous flightless birds went extinct 45,000 to 55,000 years ago after humans scorched their habitat.

What did the first birds eat?

An international team of scientists has analyzed hundreds of eggshell fragments from an extinct flightless bird called Geniornis that lived 130,000 to 50,000 years ago. Carbon isotopes from eggshells reveal what the birds ate when they laid their eggs. It was discovered that Geniornis's diet was strict and always included grass.

The largest ancient bird capable of flight

At the end of the Tertiary period (1 million years ago) and throughout the early Pleistocene, or glacial era, the number and diversity of birds reached a maximum. Many of today's species emerged, as well as others that later became extinct. Teratornis incredibilis from Nevada (USA), a huge condor-like bird with a wingspan of 4.8–5.1 m; was probably the largest known bird capable of flight.

Difference between birds and mammals

Characteristics specific to the class of birds are primarily associated with the ability of these animals to fly, although some of their species, such as ostriches and penguins, lost it during their later evolution. What makes them stand out even more is their feathers, which are not found on any other animal. They differ from most mammals in that they lay eggs.

Extinct and endangered birds

The first documented case of this kind was the destruction of the dodo. Mauritian dodo Raphus cuculatus large flightless pigeons, resembling turkeys in appearance, three species of which lived on three islands of the Mascarene archipelago in Indian Ocean(Mauritius, Reunion and Rodrigues). They were quickly destroyed by humanity almost immediately after their discovery: the archipelago was discovered in 1507, the last dodo was seen in Mauritius in 1681. In the 174 years after the discovery of Mauritius by Europeans in 1507, the entire population of these birds was exterminated by sailors and the animals they brought on their ships. On Reunion Island, the last bird was killed in 1750; on Rodrigues Island, the last bird also did not survive until the end of the 18th century.

The most famous extinct birds

Passenger pigeon
In 1914, Martha, the last representative of a previously large genus, died at the Cincinnati Zoo (North Carolina, USA). passenger pigeons (Ectopistes migratorius). Passenger pigeons were mercilessly exterminated for meat.

The first species to become extinct at the hands of man North America
...became great auk (Alca impennis), extinct in 1844. It also did not fly and nested in colonies on the Atlantic islands near the continent. Sailors and fishermen easily killed these birds for meat, fat and to make bait for cod.

Soon after the disappearance of the great auk, two species in the east of the North American continent became victims of humans. One of them was Carolina parrot (Conuropsis carolinensis). Farmers in large quantities these flocking birds were killed as thousands of them regularly raided the gardens.

100 species of birds have disappeared
Since 1600, perhaps 100 bird species have become extinct worldwide. Most of them were represented by small populations on sea islands. Often incapable of flight, like the dodo, and almost unafraid of man and the small predators brought by him, they became easy prey for them.

Many species of birds are also on the verge of extinction. Currently, many species of birds are also on the verge of extinction or, at best, are threatened by it. In North America, the California condor, yellow-legged plover, whooping crane, Eskimo curlew and ivory-billed woodpecker (possibly already extinct) are in the worst position. In other regions, the Bermuda typhoon, the Philippine harpy, the kakapo (owl parrot) from New Zealand, a flightless nocturnal species, and the Australian ground parrot are in great danger.

Birds at risk of extinction

IN natural conditions only one lives nowadays blue macaw (Cyanopsittaspixii), however, approximately 30 of these birds are kept in captivity.

Hawaiian Warbler, lepidopteran mojo (Moxobracattus), considered completely extinct and rediscovered only in 1960, apparently, is represented by only 2 pairs of individuals.

There are less than 20 survivors in the world (mostly in captivity) Red-legged Ibis (Nipponia nippon), but they are all apparently too old to reproduce.

As a result of uncontrolled hunting New Zealand owl parrot (Strigops habroptilus) was on the verge of extinction. The second reason for the extinction is that this flightless bird cannot escape from predators, so only 10 specimens remain alive.

Nowadays, only a few exist in natural conditions. California condors, bred in captivity and released in 1992.

Other known extinct bird species include

Labrador eider Camptorhynchus labradorius.
Samoan moorhen Gallinula pacifica.
White plume Porphyrio albus.
Mauritius blue pigeon Alectroenas nitidissima.
Norfolk ground pigeon Hemiphaga argetraca.
Slender-billed nestor Nestor productus.
Cuban macaw Ara tricolor.
Cayman bluebird Turdus ravidus.

The birds listed above found themselves in an unenviable position mainly due to the fault of humans, who brought their populations to the brink of extinction through uncontrolled hunting, ill-considered use of pesticides, or radical transformation of natural habitats.

26 species of birds and 132 species of mammals are now on the verge of extinction.

Forest inhabitants of the Chinese province of Liaoning 130 million years ago. A small four-winged dinosaur, Microraptor gooi, hovers in the foreground. Cathayornis flying on the right are also not considered birds. But on the left on the branch sits Confuciusornis, representing one of the evolutionary lines close to birds. It is obvious that various groups of feathered animals tried to master the air environment in the Cretaceous period

Until recently, the early evolution of birds represented perhaps the darkest chapter in the fossil record. And although recent paleontological discoveries have clarified a lot, it is not possible to read it completely. What is known is that birds evolved from reptiles. But from which ones exactly? The direct ancestors of modern birds have never been found, and plumage and the ability to fly arose repeatedly in various animals of the Mesozoic era. There are more than enough hypothetical ancestors: among them are pseudosuchians, ornithosuchians, pterosaurs, dinosaurs and even crocodiles. But Archeopteryx, familiar to everyone from the picture in a school textbook, has to be crossed out from this list.

Birds, along with insects, are the main inhabitants of the Earth's air spaces. Several devices allow them to take to the sky and control their movements in flight. First, a special skeleton. A complex wing is capable of holding the entire weight of the body in the air. Its swing movements depend on the structure of the shoulder girdle, formed by the scapula, coracoid, sternum and clavicles fused into a fork. There, for example, there is a three-bone hole through which passes the tendon of the muscle that lifts the wing up after it is lowered. To hold the tail feathers, which serve as a rudder in flight, the end of the spine formed a short and wide bone - the pygostyle. Secondly, plumage helps birds fly. Controllability in flight is provided by very specific feathers: flight feathers and tail feathers. But there are also feathers, the purpose of which is different: they create a streamlined body shape for birds both during flight and when diving, serve as a heat-protective cover and, being brightly colored, help in communication between relatives.

Apart from birds, the only vertebrates currently able to fly are bats and fruit bats. However, they have a fundamentally different wing structure and no feathers, which makes their flight unlike that of a bird. In the past, the variety of flying and feathered creatures was extremely large. In addition to the long-known pterosaurs and archeopteryxes, paleontologists have discovered large number unusual species, the existence of which was not even suspected. It seems, fauna there was no shortage of people willing to conquer the sky.

There are two main hypotheses for animals acquiring flapping flight: from faster running on the ground or from jumping and gliding from some elevated places - trees, rises in the mountains. The latter hypothesis received indirect confirmation after the discovery of various feathered dinosaurs in China, in the Liaoning province. Now most scientists believe that flying species came from the environment of the forest-dwelling, probably some very small, no larger than a pigeon, species of reptiles and birds. Their descendants quickly passed the primitive stage - gliding from elevated places - and learned to fly for real. How long did all this take, how many species changed before birds acquired flight? No one will say, since the flying creatures found by paleontologists may not have been the first, and the very beginning of the evolution of birds is still hidden from us.

For a long time it was believed that the plumage of birds is the scales of reptiles modified over millions of years of evolution. However, the results of the latest research cast doubt on this. Both plumage and scales, like all integumentary formations in vertebrates, originate from the cells of the outer layer of the skin - the epidermis. Reptile scales consist of so-called alpha-keratin, a protein with short peptide chains. It is formed from protruding areas of one outer layer of the epidermis. During the development of feathers in birds, a tubercle of the epidermis also first appears, but it is formed not by one, but by its two outer layers. Then this tubercle sinks inside the skin, forming a kind of sac - a follicle, from which the feather grows. Moreover, the material for the feather is slightly different - beta-keratin, composed of long peptide chains, which means it is more elastic and strong, capable of supporting the feather plates. Alpha-keratin is also present in birds; it is used to form the covering of the beak, claws and scales on the tarsus. In addition, the feathers of birds have a tubular structure, and the scales of reptiles are solid. Apparently, the feather is an evolutionary innovation that has proven its usefulness over time.

Plumage that easily acquires different shape and coloration, opened up almost unlimited possibilities for birds for various types of flight, the development of signal and identification structures, and the development of many ecological niches. It was plumage that helped birds achieve the enormous diversity that we now see. Almost ten thousand species are more than all other land vertebrates.

If most feathered dinosaurs couldn't fly, why did they need down or feathers? Clearly not for flying. In any case, not immediately for the flight. It is possible that various downy formations arose among predatory lizards as a thermal insulation cover, as indicated by paleoclimate data. In the middle and end Triassic period(230-210 million years ago), when the first dinosaurs appeared, a cold snap occurred on Earth. Along the outskirts of the huge continent of Pangea, the only one at that time, latitudinal climatic zones with cool humid climate. The animals that lived there adapted to the cold, including with the help of plumage. On the contrary, the center of Pangea was occupied by dry and desert areas with high level solar radiation, since cloudiness was rare in those parts. To protect against radiation, reptiles again used down and feathers. Over time, the feathers at the ends of the forelimbs, on the tail and on the head could turn into elongated feathers that served as decorations or identifying marks. They became the basis for the appearance of flying feathers in some dinosaurs. In a similar way, other reptiles could have acquired plumage, among which were the distant ancestors of birds.

Doesn't appear in birds

For almost 150 years, since the first discovery, Archeopteryx was considered the progenitor of modern birds. In fact, other than knowledge about this creature, scientists for a long time had no other information about the origin of birds. It would seem that such features as plumage and wings undeniably indicated that Archeopteryx was the oldest bird. On the other hand, in terms of the structure of the skull, spine and other parts of the skeleton, it was similar to predatory dinosaurs. These observations gave rise to the hypothesis about the origin of birds from ancient lizards, which has now become especially popular.

As often happens in science, an alternative hypothesis also found support. Long-expressed doubts about the direct relationship of Archeopteryx and birds (they are too different anatomically) have turned into conviction, since since the early 1980s, paleontologists have found feathered dinosaurs, ancient birds, and their close relatives. New skeletons of Archeopteryx were also found. Today, ten of them are known, all of Upper Jurassic age (145 million years ago) from the Altmühl River in Bavaria. The last specimen, which is better preserved than the others, described at the end of 2005, finally convinces that Archeopteryx comes from predatory dinosaurs, but has nothing to do with modern birds. He is something else: not a dinosaur, but not a bird either. I had to look for another candidate for the role of the ancestor of birds.

Dinosaur down jacket

The existence of feathered dinosaurs has long been suspected, but there has been no evidence of it. They appeared in the 1990s in China, in Liaoning province. There, paleontologists discovered a whole cemetery of forest flora and fauna 130-120 million years old. What makes the event unique is the excavation natural area. Marine or near-aquatic communities of animals and plants are usually available for study due to better conditions burials. Forest, steppe or mountain inhabitants of the past most often are not preserved in a fossil state, because they are quickly converted into dust by bacteria. And here is a snapshot of forest life in the mid-Cretaceous period, recorded by volcanic ash.

The first discovered skeleton of a lizard with short grooves similar to fluff along the contour of the entire body - Sinosauropteryx prima - caused numerous disputes: not everyone agreed that the small grooves on the fossilized clay were left from fluff. Then they dug up another creature, which, no doubt, already had feather imprints on its tail and front legs. For its resemblance to Archeopteryx, it was given the name Protarchaeopteryx robusta. On the limbs of another dinosaur, Caudipteryx zoui, the feathers grew even thicker, and the body was covered with fluff.

Now more than a dozen lizards have been described, with surprisingly varied feathers: from short down to real asymmetrical feathers on the limbs, indicating the ability to fly. In addition, the skeleton of these predatory dinosaurs revealed some features characteristic only of birds: a fork, hook-shaped processes on the ribs, and a pygostyle. But still, these were not birds, but small predators that moved mainly by running. With long tails, toothy, scaly skin, shortened front legs and long clawed toes. Judging by the structure of the skeleton, most of them could not really fly, that is, flap their wings. Only one species is known that has risen one step higher. This is Microraptor gui - an interesting specimen of a small dromaeosaur, found there, in Liaoning. All in fine plumage, with a crest on the head. Its front legs were covered with asymmetrical (with narrow outer and wide inner webs) flight feathers exactly like those of birds. The hind legs were also covered in flying feathers, longer on the metatarsus and shorter on the lower leg. It turns out to be nothing more than a four-winged feathered dinosaur that could fly from tree to tree. However, he turned out to be a poor flyer. In the absence of binocular vision (when the field of view of both eyes overlaps), Microraptor could not accurately target its landing site and descended into the trees, apparently rather awkwardly.

It would seem possible to assume that birds descended from predatory dinosaurs soaring among the trees. However, too significant anatomical differences between them do not allow this to be done. So there is no need to rush and record feathered dinosaurs as the ancestors of birds.

Established competitors

Living side by side with feathered dinosaurs were enantiornis, which in Greek means “anti-birds,” creatures especially important for understanding the evolution of birds. Judging by the findings, this was the largest and most diverse group of flyers that lived in the Cretaceous period.

Externally, enantiornhis closely resembled modern birds. Among them there were small and large species, toothless and toothed, running, waterfowl, arboreal, and, most importantly, they all flew perfectly. There was also a lot of familiarity in the skeleton: the same bones of the wing, torso and hind limbs. Only some things articulate differently in the shoulder blade, some in the heel, lower leg and spine. Small differences at first glance. And the end result is a different wing lifting system and footwork. Most real birds can move their feet in different directions: turn in, turn out. This helps predators, eagles and falcons, to deftly grab and hold their prey. The legs of enantiornis (many of which, by the way, were also predators) are designed differently, which is why they walked on the ground, rather, clumsily waddling from side to side, like geese. All this greatly distances Enantiornis from real birds. It turns out that their external similarity is formal. Just as the tail of the aquatic lizards ichthyosaurs is similar to the tail of fish, so the paws and wings of enantiornis are similar to the paws and wings of real birds.

Many anatomical features make Enantiornis similar to carnivorous dinosaurs. This is confirmed by the findings of embryos inside fossil eggs in Mongolia. It turned out that the bones of the skeleton were finally formed in these primitive birds very early. The joints of the unhatched chicks were already bone, like dinosaurs, and not cartilaginous. In chicks of modern birds, the joints remain cartilaginous for a long time and only after a few months are replaced by growing bone. In addition, cross-sections of enantiornis bones show lines of growth retardation, similar to growth rings on tree trunks. This suggests that their bones did not grow to their final size in one season, but were formed in cycles over several years, slowing down during the cold seasons of the year. This means that antibirds could not maintain their body temperature at a constant level - just like reptiles. Apparently, it was the carnivorous dinosaurs that were the ancestors of enantiornis. About 67 million years ago, both of them became extinct, leaving no descendants behind.

An ancestor who may not exist

For a long time it was believed that true birds, or fantails as they are also called, appeared at the beginning Cenozoic era, that is, no earlier than 65 million years ago. And suddenly finds 100 and 130 million years old began pouring in from the United States, Mongolia and China. At first they didn’t even believe the age determinations, but subsequent work confirmed that, yes, during the time of dinosaurs and enantiornis, fan-tailed birds were already found. They looked just like modern ones and even achieved some variety. Where did they come from if the feathered and flying creatures discussed above are not suitable as their ancestors? Now there is only one assumption.

In 1991, American paleontologist Shankar Chatterjee described what he found in Texas unusual creature, in many ways similar to birds. Its age is 225 million years, which is 80 million more older than age Archeopteryx. The creature was called Protoavis texensis - “proto-bird”, and not without reason. His voluminous skull contained a fairly large brain with hemispheres and a cerebellum, which other vertebrates did not have in the Late Triassic time when he lived. Judging by the structure of the skull, Protoavis had binocular vision and wide-set large eyes, which indicates its ability to hunt deftly and navigate well in the surrounding world, as is typical of birds. In general, the skeleton of Protoavis has many features similar to fan-tailed birds, but the proportions of the body, short and powerful limbs, and the position of the center of gravity indicate that it could not fly. And he apparently had no feathers. Despite this, Protoavis is more similar to a real bird than Archeopteryx, and at this moment it is Protoavis that can be considered the closest ancestor of modern birds. If this is so, then their evolution should be carried out not from dinosaurs, but from more ancient reptiles, united in the group of archosaurs.

The discovery of protoavis made it possible to find an answer to another question: how do birds differ from dinosaurs? Because birds expend enormous amounts of energy to fly, their metabolic rate is much higher than that of reptiles. In birds, oxygen consumption during metabolism per kilogram of weight is 3-4 times higher than in reptiles. Since the metabolic rate is high, therefore, toxins must be removed from the body quickly. This requires large, powerful buds. In modern birds, the pelvic bones have three deep cavities in which these large buds are located. The same cavities for the kidneys are also present in the pelvic bones of Protoavis. Obviously, his body had a high level of metabolism, unusual for reptiles.

Everything would be fine, but the reconstruction of Protoavis does not inspire confidence in many paleontologists. Its remains were interspersed with the bones of other reptiles; in such conditions, it is not surprising to confuse and count parts of two or even several different animals as a single creature. In general, for final conclusions we must wait for other finds, and modern birds will remain without direct ancestors for now.

However, like ancient birds without direct descendants. Because it is not possible to trace the evolution of birds sequentially from beginning to end. There are still plenty of gaps. In particular, no intermediate links have been found between the ancient fantails, which still retained the features of reptiles - teeth growing from the alveoli, abdominal ribs and long row vertebrae in the tail, and modern groups of birds. Suddenly, as if out of nowhere, ancient geese, loons, albatrosses, cormorants and other aquatic birds appeared at the end of the Mesozoic era.

As a hypothesis

So, we saw a number of amazing feathered creatures that lived on Earth at least at the end of the Mesozoic, from 145-65 million years ago. At that time, the world was full of animals trying to master the airspace. In addition to the ubiquitous enantiornis, the seas of North America were inhabited by toothy, gannet-like ichthyornis. Hesperornis lived in the Late Cretaceous in the seas of ancient Eurasia. In Europe, there were gargantuavis, a bird of unknown origin the size of a turkey. The forests of Mongolia and China were inhabited by arboreal Ambiorthus, Liaoningornis and feathered dinosaurs. And there are many more single forms whose position on the evolutionary tree of birds is difficult to establish. Only two branches can be clearly traced: from protoavis to fan-tailed birds and from feathered dinosaurs to Archeopteryx and then enantiornis.

A number of fossil forms are known that have not progressed beyond planning. While real flapping flight was achieved only by pterosaurs (we are not discussing them here, since they are not at all related to birds), microraptor gooi, enantiornis and real fan-tailed birds. All of them were successful in mastering air environment. Pterosaurs reigned in the air for 160 million years, enantiornithes for at least 80 million years. Both of them were probably surpassed in competition by fan-tailed birds, which have spread widely across the planet in the last 65 million years.

Over the past couple of decades, paleontologists have shown that parallel evolution is a widespread path among living things. There were several attempts among invertebrates to become arthropods, among ancient fish to come to land and become amphibians, among reptiles to become mammals, among plants to acquire flowers and become angiosperms. But usually only one or two of them turned out to be successful in the future.