In a series of papers published by Ostrom (a scientist at Yale University in the US in the 1960s), he went on to identify a set of common features between Archeopteryx, Deinonychus and other theropods. Based on these studies, he came to the conclusion of where birds came from - that birds are direct descendants of small theropod dinosaurs.
When he collected evidence of the origins of birds, in the natural museums of New York and Paris, a new method was used to decipher the connections between organisms.
Where did birds come from - birds are dinosaurs!
This method, called phylogenetic systematization, or more generally cladistics, became the standard for comparative biology, the application of which clearly confirmed Ostrom's conclusions. Cladistics groups organisms solely on the basis of certain types of common traits, which is particularly informative.
This method is based on Darwin's law, according to which evolution continues provided that a new hereditary trait arises in a certain organism and is genetically transmitted to its descendants. This law states that two groups of animals with a common set of such new “acquired” traits are more closely related to each other than to species, and exhibit only the original traits.
Today, the theropod-to-bird lineage cladogram shows that for the bird (Aves) clade it consists of the Archeopteryx ancestor and all its other descendants. It is a subgroup of a broad clade that includes the so-called maniraptor theropods, a subspecies of tetanuran theropods descended from the first theropods.
These archaic theropods in turn evolved from non-theropod dinosaurs. The cladogram shows that birds not only evolved from dinosaurs, they are them, just as humans are mammals, although humans are as different from other mammals as birds are from other reptiles.
Where did the birds come from? Looking at the birds from the depths of the primary forests of the early Melka, we will notice only their slight similarity with modern ones. These early birds may have spent most of their lives in trees, were able to nest, but there is no evidence that they were capable of nesting, had complex songs, and migrated long distances.
They did not fledge like modern birds and did not grow as quickly as today. However, there is no doubt that they looked rather strange - with clawed fingers and toothy beaks. However, during the Early Cretaceous, some skeletal features became similar to modern ones, which made it possible to fly quite well.
Then an additional wing appeared - part of a bird's wing, necessary for controlling flight at low speed, as well as a long first finger, intended for shrinking the nest.
Where did birds come from - ornithologists, wading through the thicket after fifty million years, could again encounter representatives of birds of very primitive origin. Among them one could recognize early representatives of modern species.
At least four major lineages of modern birds—among them the ancient relatives of shorebirds, sea loons, ducks, and geese—were already in existence several million years before the end of the Cretaceous.
Most bird species evolved during the Cretaceous and became extinct at the same time.
From whom did birds descend? There is no reason to doubt that all species of birds - modern and extinct - descend from small carnivorous theropod dinosaurs. So, modern birds are nothing more than small, feathered, short-tailed theropod dinosaurs!
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 structured 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 reptile 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 earth 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 with 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 the mass extinction of the dinosaurs at the end of the 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
The skeleton of the lizard Unenlagia comahuensis, the "long bird", found in May 1996 in Argentina, fills the gap separating the ancient theropod reptiles and the first bird, Arechaeopteryx.
Differences between birds and reptiles
The higher development of birds is evidenced by an enlarged brain (in particular, the large size of the cerebral hemispheres and cerebellum in birds), the perfection of the respiratory and circulatory systems - double breathing and the 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
The remains of an extinct bird resembling a magpie that lived in the second half of the 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 small bird had sharp, slotted teeth, a long lizard-like tail, and forelimbs with three toes 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 clasp 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 link between birds and reptiles known to science, 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 discovered 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 explorer Goudeau found half an eggshell in Madagascar so large that it could be used as a water container. 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, it appears at a certain time of the year, and in everything the vulture is not the same as we think and how it is depicted. 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 of India - Mohenjo-Daro. made about five thousand years ago. Radiocarbon dating of the bird's bones helped determine 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), living on the islands of New Zealand, presumably until the beginning of the 19th century, was probably even greater in height - 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 period, 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 the 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.
First North American species to become extinct at the hands of humans
...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 killed these flocking birds in large numbers as thousands of them regularly raided 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 in our time 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 its 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.
The question of the origin and evolution of birds has been clarified only in the most general terms. There is no doubt that their ancestors were ancient reptiles. The separation of the branch of reptiles, which ultimately led to birds, must be attributed to the very beginning of the Mesozoic (Triassic). Closest to birds are pseudosuchia (Pseudosuchia), which gave rise to dinosaurs, crocodiles and some other groups of reptiles. Among them, ornithosuchus (Ornithosuchus) especially stood out, showing the greatest morphological similarity to birds. Like birds, they moved on their hind legs, and their forelimbs were used for grasping food. The tail was long. There were also similarities in the structure of the pelvis, which amounted to a significant strengthening of this formation. The outer integument consisted of elongated scales with a longitudinal axis, from which short grooves branched off on the sides, so that the scale to a certain extent resembled a feather in its structure.
Pseudosuchians themselves were highly specialized reptiles and were not the direct ancestors of birds. The phylogenetic roots of the latter must be sought among even more ancient reptiles, which also gave rise to pseudosuchians. The evolution of this group apparently proceeded by initially adapting to climbing trees, in connection with which the hind limbs remained a tool for supporting the body on a solid substrate, and the forelimbs were specialized for climbing by grasping branches with the fingers. Subsequently, the ability to jump from branch to branch developed. The scales covering the outer part of the forelimb elongated, forming the rudiments of a wing plane.
Let us recall the amazing ability of the chicks of modern hoatzins to climb trees using their wing fingers. Climbing trees caused an adaptation in the form of opposition of the first toe of the hind limbs to the remaining toes. The next stage was the expansion of the edges of the scales and their transformation into feathers, which first developed on the wings and tail, and subsequently spread throughout the body. The appearance of feathers not only made it possible to fly (initially, apparently, only to flutter), but also played a very important thermal insulating role, i.e., it largely determined the homeothermy of birds.
The immediate ancestors of birds have not yet been discovered. In the fossil record there are four facts of discoveries of amazing animals that, in a certain sense, occupy an intermediate position between reptiles and birds. In the last century, first a feather imprint and then two relatively complete skeletons were found in Jurassic deposits. According to one of them, Archeopteryx was described, and according to the other, the closely related Archaeornis. Later it was proven that Archaeornis is not an independent species and was described from a different print of Archeopteryx. These animals, of course, have avian features: the feather cover, the forelimbs modified into wings, the saber-shaped shoulder blades fused into the arch of the collarbone, the structure of the pelvis, the presence in the hind limbs of a fused metatarsus - the tarsus - and the first toe, opposed to the other three toes. Along with this, these animals are characterized by many features of reptiles: the absence of a horny beak. The presence of teeth, a long (about 20 vertebrae) caudal spine, a narrow and keelless sternum, and abdominal ribs. The three fingers of the forelimbs were distinctive, well developed and armed with claws; the pelvis is connected to four to six vertebrae, and not fused, like in birds.
Analysis of the structure of Archeopteryx gives grounds for assumptions about their way of life. They were arboreal, climbing animals that could flutter and glide, but not fly. This is evidenced by the weak skeleton of the forelimbs, loose fingers, weak sternum without a keel and the smooth surface of the wing bones, indicating the absence of powerful flight muscles. Judging by the structure of the pelvis, they laid small eggs, the size of ¼ chicken eggs. Weak teeth indicate feeding on insects or fruits. They could hardly walk on their hind legs alone, but they climbed trees well, as evidenced by the structure of their limbs and their girdles.
No links connecting the first birds with real flying birds have been found. Two very distinctive groups of birds are known from the deposits of the Cretaceous period: ichthyornis (Ichthyornis) and hesperornis (Hesperornis). Hesperornis were aquatic birds that did not have the ability to fly. There were no wings, and their forelimbs were represented only by the rudiments of a shoulder. The sternum had no keel. The birds led an aquatic lifestyle and rowed while swimming with well-developed hind legs. Outwardly, they somewhat resembled loons. Ichthyornis were good fliers, as can be judged by the developed wing skeleton and large sternum with a high keel. Both groups had jaws armed with teeth.
In the Tertiary period, quite typical birds very close to modern ones appear. In the Eocene, toothed forms (Odontopteryx), systematically close to modern copepods, are still found, but passerines, swifts, woodpeckers, rollers, waders and other modern groups already appear. In the Oligocene and especially in the Miocene, the similarity in the composition of the avifauna becomes even greater. A lot of representatives of modern genera appear: eagle owls, owls, flamingos, herons, lapwings, hazel grouse, loons, gulls, coots, geese, etc.
Summarizing the above, we come to the conclusion that the ancestors of birds were Early Mesozoic reptiles, systematically close to pseudosuchians. Initially, they represented land animals that ran only on their hind legs.
Their forelimbs had a grasping function. Subsequently, the lifestyle became arboreal climbing. The ability to jump and then to glide began to develop, which was associated with the growth and elongation of the scales. The ability to flutter from branch to branch, from tree to tree and back has appeared. The development of this ability led to the emergence of flight. The initial environment for birds was the forest. This is evidenced by the fact that we now find the largest number of bird species and the greatest diversity of ecological types in the forest.
Simultaneously with the adaptation to flight, many structural features were improved. The appearance of feather cover served as the most important prerequisite for homeothermy.
The hypothesis that birds evolved from reptiles was put forward in the second half of the 19th century. However, the question of the origin of birds still causes heated debate among paleontologists.
Ancestors
The problem is the lack of avian ancestors or the “first bird.” The found prints are interpreted differently and not a single find is definitely considered the ancestor of modern birds. Briefly talking about the origin of birds, we should describe the most significant finds that give an idea of the origin of birds from reptiles.
- Archeopteryx . The very first find discovered in Bavaria in 1861. Based on the discovered prints, a small creature the size of a crow was described that lived about 150 million years ago. The presence of feathers indicates that they are birds. Anatomically more similar to a reptile. I couldn’t fly fully. Perhaps he was just planning from branch to branch. However, Archeopteryx is classified in the class Birds, subclass Lizard-tailed.
Rice. 1. Archeopteryx is the most ancient bird.
- Enantiornis . The remains of ancient birds were discovered in Argentina in 1981. They lived 70-65 million years ago and had the characteristics of birds: they had well-developed wings and could fly. The presence of teeth and the structure of the skeleton make the find similar to Archeopteryx.
- Confuciusornis . The oldest bird to independently lose teeth was found in China. Lived about 120 million years ago. The beak was covered with a horny sheath. In some respects, the skeleton is similar to modern birds.
- . They lived between 168 and 66 million years ago. This extensive family, belonging to the suborder Theropods, order Saurischians, contains several species of feathered dinosaurs (Deinonychus, Utahraptor, Sinornithosaurus). The most significant is Microraptor, or the “four-winged dinosaur,” which had wing-like surfaces on its fore and hind limbs.
Rice. 2. Dromaeosaurids.
- . Found and described in China in 2009. Belongs to the Troodontidae family, Lizard-pelvic order. Lived 167-155 million years ago. It reached 30-40 cm in length and weighed 100 g. It had plumage, a long tail, and a beak.
Rice. 3. Anchiornis.
There are other forms that indicate the presence of feathers in dinosaurs. For example, Caudipteryx, which lived 120-125 million years ago, had fan feathers on its tail, which most likely served to attract a sexual partner.
Evolution is not a linear process. The forms found indicate attempts by different species to master the airspace. Exactly which lineage the birds originated from remains to be seen.
Hypotheses
Analysis of the finds allowed us to formulate a hypothesis of the origin and evolution of birds from their dinosaur ancestor. The first birds appeared during the Jurassic period (between 201 and 145 million years ago). Troodontids and dromaeosaurids - "feathered dinosaurs" - were long thought to be the closest ancestors of modern birds.
Reptiles acquired the ability to fly after mastering trees. By retaining claws on their front limbs and powerful hind limbs, dinosaurs could climb trees. In the process of evolution, they acquired the ability to glide using modified scales, which later became feathers. According to another hypothesis, reptiles learned to fly “from the ground”, jumping after insects.
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The well-coordinated “dinosaur” hypothesis began to have opponents when, in 1991, in Texas, Shankar Chatterjee found two fossil birds - protoavis, who lived 220-200 million years ago, i.e. 50-70 years earlier than Archeopteryx. Unlike the "Bavarian bird", Protoavis has more features in common with modern birds. This means that theropods that lived later than Protoavis are at best “brothers” and not direct ancestors of birds. This hypothesis was actively supported by paleontologist Evgeniy Kurochkin.
Chatterjee's find was met with harsh criticism. Many paleontologists believe that Chatterjee found a chimera - bones belonging to different animals. It is unscientific to base a hypothesis on such data.
The first warm-blooded egg-laying animals. The birds' body is covered with feathers, the forelimbs have turned into wings, and the jaws form a beak. Birds have adapted to different habitats, to different food sources and have spread widely across the Earth. The class includes about 9,000 species, which are grouped into 40 orders.
Birds are divided into two subclasses: lizard-tailed birds and fan-tailed birds.
Subclass 1. Lizard-tailed, or ancient birds. This includes only Archeopteryx, a fossil bird.
Subclass 2. Fantails, or true birds, are divided into three main superorders.
Superorder 1. Ratites, or ostriches. This includes African, South American and Australian ostriches and kiwi. All of them are exclusively running birds with underdeveloped wings and a flat, keelless sternum. The sizes, excluding kiwi, are very large. The coccygeal gland is absent.
Superorder 2. Penguins. Birds of Antarctica, but following cold currents, can penetrate far to the north, in some places to the equator. These are not flying birds, but excellent swimmers and divers, which differ from all other birds in their forelimbs modified into flippers and a primitive tarsus. The largest, the emperor penguin, weighs up to 40 kg.
Superorder 3. Carinae. This includes all other birds, of which there are about 15 thousand species.
Basic characteristics of birds.
The body is covered with feathers, which perform a thermal insulation function and ensure streamlining of the body. The skin is thin, elastic, and practically devoid of glands. There is only the coccygeal one.
There are no teeth in the skeleton; they have been replaced by horny sheaths on the beak.
The transformation of the forelimbs into wings was accompanied by a restructuring of the skeleton and muscles of the limbs and shoulder girdle.
Transformation of the skeleton and muscles of the hind limbs and pelvic girdle provided the possibility of bipedal walking on a solid substrate and swimming. A tarsus appeared in the foot, and four toes remained.
Pneumatization of the bones occurred, which increased their strength. A powerful keel has formed on the sternum.
The musculature is more differentiated than in reptiles. The muscles that move the wings are the most well developed.
The stomach consists of two sections - glandular and muscular. The intestine opens into the cloaca. Birds are characterized by eating a wide variety of foods and fast digestion.
Complete separation of the systemic and pulmonary circulation contributed to a better supply of tissues with oxygen and nutrients. A four-chambered heart emerged. The right aortic arch is preserved, and the left one is reduced. The arterial trunk is represented by two vessels - the pulmonary artery and the right aortic arch.
There was an intensification of breathing due to the system of air sacs connected to the lungs. The lungs themselves are small, spongy, attached to the ribs and spine. Double breathing appeared.
There is a progressive development of the forebrain and cerebellum, and due to flight, the sense organs become more complex, especially the organs of vision.
The excretory system lacks a bladder and pelvic kidneys.
Increased but constant body temperature allowed the birds to master zones with cold climates.
In female birds, reduction of the right ovary and oviduct occurred. Eggs with a large supply of nutrients. Birds incubate a clutch of eggs and take care of their offspring.
Birds are similar in many morphological characteristics to reptiles: the presence of horny scales on the limbs, the almost complete absence of skin glands, a similar structure of the genitourinary system, the nature of embryonic development, the scheme of the peripheral circulatory system and the presence of one occipital condyle.
