How the first bird appeared. The origin of birds: features, interesting facts and description. Importance and protection of birds. Ancestors - waterfowl
In 1861, on the territory of southern Bavaria, the remains of Archeopteryx were discovered - a feathered creature the size of a crow that lived about 145 million years ago. As many scientists believed, it was he who was the ancestor of modern birds. But for more than a century in paleontology, there was a gap between him and real birds, not filled with other finds. Only in the last 20 - 25 years, with the discovery of many new birds of the Mesozoic era, it became clear: 140 - 110 million years ago, their world was rich and diverse. True, different scientists interpret these findings differently. Which of the hypotheses put forward by them is closer to the truth, and therefore to understanding the paths and laws of evolution?
In the view of the general public, paleontologists are specialists who find and study mammoths and dinosaurs. Indeed, their huge skeletons in museums attract attention and amaze the imagination. But well-preserved specimens are rare. Much more often, individual bones, teeth and skulls can be found in the earth's layers, they describe the appearance of extinct animals and study their kinship. Fossil giants basically show us only finite, highly specialized results of evolution. The origins of most groups of vertebrates are among small and inconspicuous creatures without much anatomical diversity. Moreover, in this state, they replaced each other for many millions of years, then either died out, or found another free niche of life, where their wide, as experts say, adaptive radiation began, i.e. many new species appeared, adapted to the changed environmental conditions.
ARCHEOPTERIX
The history of birds and their flight remained a mystery for a long time. Although these questions were posed by science even before the appearance of Charles Darwin's work on the origin of species. In the middle of the XIX century. almost simultaneously with the publication of this famous work, Archeopteryx was discovered, which was perceived by natural scientists as a triumph of evolutionary theory. It seemed that here it is - the missing transitional link between reptiles and birds. Until now, in textbooks, from school to university, you can read that birds are flying creatures covered with feathers, with one legalized ancestor - Archeopteryx - a transitional form from reptiles.
Immediately after the discovery of the first specimen (by now there are already 10 known), some scientists expressed doubts that it was Archeopteryx that was the ancestor of other birds. If we consider as such all those who have wings, feathers and are able to fly, he is suitable for the great-great-grandfather of a sparrow. If you immerse yourself in anatomy, the sparrow does not work out of him: functionally he is like a bird, but structurally - a pure reptile. In addition to the feather, it has nothing in common with real birds: the skull is arranged differently, the vertebrae are not the same, the front limbs, although they have become wings, but the details of the structure of their skeleton are different, the same applies to the legs.
Researchers were divided. Some argued: birds descended from the ancient, lizard-like thecodont reptiles; others believed that Archeopteryx and beyond it all other birds trace their ancestry to carnivorous (theropod) dinosaurs.
In 1926, a solid book by the Dane Gerhard Heilmann "The Origin of Birds" was published on English language... The author's conclusions are unambiguous: birds were "born" from thecodont reptiles, not from carnivorous dinosaurs. According to scientists, theropods themselves - predatory dinosaurs - originate from the thecodonts.
Archeopteryx does have a lot in common with the latter. Their close relationship was analyzed in detail and confirmed in the 1970s by the American paleontologist John Ostrom. But he considered Archeopteryx to be the most ancient bird. This hypothesis is now adhered to both by supporters of the origin of birds from theropods, and by their opponents, who believe that Archeopteryx originates from predatory reptiles - archosauromorphs, more ancient than theropods. If this is so, then for one and the other hypotheses it is necessary to accept that evolution proceeds sequentially, in a straight line, from simple to complex. And this does not happen in nature. The entire experience of paleontological and modern molecular genetic research of recent decades shows: evolution is proceeding on a broad front, by trial, through achievements and mistakes, in beams of parallel developmental lines. And new data on the historical development of birds illustrate well just such a character of evolutionary laws. This is why reasoning about feathers and bones becomes key to understanding the main problems of her theory.
FAN OF NEW FACTS
For almost 150 years, hypotheses about the origin and relationship of birds were based almost exclusively on the study of Archeopteryx. The history of Cenozoic birds (to which all their modern representatives belong) for the last 65 million years has also been well studied. From the Mesozoic era, from the creatures of interest to us, there were only isolated rare finds that did not add up to the general picture. And suddenly there was a breakthrough.
First, in 1981, Enantiornithes were described from Argentina. Soon they began to be found on all continents in the sediments of the Cretaceous period, i.e. in the range from 145 to 65 million years ago. Outwardly similar to real birds - fully feathered, with well-developed wings, seemingly with the same paws and tails, but in terms of the details of the skeletal structure, they are completely different: they have much in common with Archeopteryx. Therefore, they can be attributed to the group of the so-called lizard-tailed, in contrast to the fan-tailed, which includes all modern birds.
Then they discovered completely unusual birds called Confuciusornithidae. Their skeleton has many primitive and original features in the structure, however, according to some features, they are similar to modern birds. In particular, their beak was covered with a horny sheath and had no teeth, and on the crest of the humerus there was a large hole of unknown purpose.
It was believed that true fan-tailed birds appeared and lived almost exclusively in the Cenozoic. But suddenly they began to be found in the sediments of the beginning of the Cretaceous period, the last in the Mesoic era, which lasted about 80 million years, i.e. longer than the entire Cenozoic. The first reliable such bird, named Ambiortus dementjevi, was found in the early 1980s in Mongolia. Then it seemed so unusual that some of the paleontologists did not believe in the reality of its existence.
And finally, a variety of theropod dinosaurs with plumage have been found in China. Moreover, in some there was a semblance of a downy cover, in others, long feathers were located only at the ends of the wings and tail, and still others were completely covered with small feathers. And suddenly scientists "met" a small dinosaur the size of a pheasant, which has preserved its real wings with the corresponding feathers, and in addition, the legs were equipped with the same feathers! Four-winged flyer! Later it turned out that different plumage is characteristic of dinosaurs from five different families of theropods (Oviraptoridae, Avimimidae, Dromeosauridae, Therizino-sauridae, Troodontidae) found on all continents except Antarctica. Moreover, even the crowning tyrannosaurs (Tyrannosauridae) of numerous carnivorous dinosaurs, most likely, were covered with feathers. What does this mean? Here the positions of the specialists were again categorically divided. Some argue: some of these dinosaurs, in fact, are not, in fact, they are birds that have lost the ability to fly, while in other dinosaurs, the collagen structures of the skin modified in a fossil state are taken for a downy cover. Other scientists believe that these findings prove the origin of real birds (along with Archeopteryx) from theropod dinosaurs.
EVOLUTION IS THE WONDERFUL FANTASY
But a different assessment of all new facts is also possible. Archeopteryx with enantiornis, having big number traits in common with theropod dinosaurs most likely originated from them, crowning one of the reptiles' attempts to master the air. Alas, it was not successful. Archeopteryx disappeared back in the Jurassic period, and enantiornis lost in competition with real birds and died out without a trace along with dinosaurs at the end of the Cretaceous period.
It turns out that real fan-tailed birds for millions of years existed simultaneously with these dinosaur birds? And did they arise from some kind of original archosauromorphs (a subclass of reptiles characteristic of the beginning of the Mesozoic) long before the flying dinosaurs? This could have happened at the end of the Triassic period (about 220 million years ago).
The Mesozoic era began about 250 million years ago and lasted for about 185 million years; is subdivided into three periods: Triassic (beginning 250 million years ago, duration about 35 million years), Jurassic (beginning 213 million years ago, duration about 70 million years) and Cretaceous (beginning 144 million years ago, duration about 80 million years).
Caudipteryx (Caudipteryx zoui Ji et al., 1998) from the Early Cretaceous of China belongs to theropod dinosaurs, but some scientists consider it a bird that has lost its flight. The caudipteryx is characterized by small feathers on the tail and ends of the forelimbs (shown by red arrows). Many caudipteryx in abdominal cavity accumulations of gastroliths have been preserved (red arrow); they are shown in magnification at the top right.
In Jeholornis (above) and Confuciusornis (below), the claws (shown by blue arrows) on the toes of the wings are bent outward, which is no coincidence: they were most likely intended to cling to branches. (Photo from the book of the Chinese paleontologist L. Hou.).
Sacred Confuciusornis (Confuciusornis sanctus Houetal., 1995) is one of the first sensational finds of Early Cretaceous birds in Liaoning Province, China. Now 6 types are described.
Longirostravis (Longirostravis hani Hou et al., 2003) from the group of enantiornis birds. The size of a starling, with an elongated thin beak, the tip of which was armed with small teeth, which probably made it possible to pull out the covered prey, holding it securely.
There is circumstantial evidence of this - finds of Late Triassic and Early Jurassic small bird tracks in South America, Africa and Europe. We do not know bird skeletons for those millions of years. However, until very recently it was not known about their presence in the deposits of the Early Cretaceous. Only traces and a large number of feathers were found, which allowed us to talk for a long time about the unknown evolution of birds during at least the Cretaceous period.
Other lineages of ancient birds are known from individual finds, which, upon careful study, do not correlate either with enantiornis, or confuciusornis, or with real fan-tailed.
It turns out that evolution has made many attempts to lift reptiles and their descendants into the sky. For various reasons, most of the experiments failed and ended in extinction. Only the fan-tailed, in the end, gave a powerful burst of adaptive radiation and mastered the air in all its layers. It turns out that evolution does not act as an economical mistress, but as a wasteful dreamer.
LIAONING PROVINCE TREASURE
Most of the sensational paleontological discoveries in recent years have been associated with the Liaoning province in northeastern China. Cretaceous localities in this region have been known to specialists since the 1920s. Previously, they were found there in a large number only fossil fish, insects and plants. But at the end of the XX century. birds and feathered dinosaurs were unexpectedly discovered. Among the first, these are true fan-tailed, and enantiornis, and confuciusornis, and several other separate genera of birds, which scientists cannot yet attribute to any of their known groups. And almost all of the mentioned feathered dinosaurs are described on the basis of materials from Liaoning. Now they were found in the Early Cretaceous and even Jurassic deposits and in other provinces of the Middle Kingdom. By the way, in addition to various birds, unknown mammals, lizards, pterosaurs, dinosaurs, turtles, amphibians, various fish, a lot of insects and rich flora materials, including the most ancient flowering plants, were found in this province. In total, more than 30 species of birds have already been described from Liaoning, the same number of dinosaurs and 6 species of mammals.
It is remarkable that many animals are represented there not just by skeletons, but also by imprints of soft tissues, external integuments (skin, scales, wool, plumage), internal organs and even the contents of their digestive system. Thus, in the place of stomachs in Caudipteryx, feathered dinosaurs from the family of oviraptorids, and Sapeomis, an ancient bird of unclear family ties, accumulations of gastroliths (small stones) have been preserved, which contributed to the grinding of plant food. In the mouth cavity of Yanornis, an ancient fan-tailed bird, remains of fish were found, in Sinosauropteryx, a small carnivorous dinosaur, the bones of a mammal, and in the mammal, Repenomamus, the remains of a dinosaur. Thus, Chinese burials make it possible to get to know the biota of this part of the world of that time in all its diversity, as well as the ecological characteristics of its individual representatives. It was named Jehol Biota.
The geological age of its deposits, established by the isotopes of argon, uranium and lead, is determined at 110 - 130 million years ago. They were formed in freshwater lakes and adjacent riverbeds and deltas. It is known that such deposits are distributed over a vast territory in many parts of China, Mongolia, southern Siberia, Korea and Japan. Why is it that only Liaoning is distinguished by its vast paleontological wealth? The fact is that strong volcanic activity was manifested in this region in the Early Cretaceous. Periodic eruptions with powerful ash emissions and the release of poisonous gases destroyed all living things, and whole animals were buried under layers of ash in lake sediments. For example, many hundreds, even thousands of specimens of the so-called "sacred Confuciusornis" (Confuciusornis sanctus) have been collected. True, they say that most of them went to private collections.
EVOLUTIONARY "LAWN"
According to our hypothesis, various birds evolved in parallel over tens of millions of years, originating among different groups of reptiles (of course, we inevitably simplify the evolutionary scenario, omitting the entire set of factual evidence already published in special scientific works, but we are trying to correctly convey the essence of the hypothetical process) ... All of the above is also supported by data from other areas of paleontology, because not only birds, but also other main classes of vertebrates evolved according to a similar scenario.
Back in the 1970s, an employee of our institute, Leonid Tatarinov (academician since 1981), showed at least 7 attempts by reptiles to become mammals, but only one or two of them were successful. Over the course of many millions of years, several evolutionary lineages of mammals existed in parallel, of which, as shown in 2007 by an employee of our institute, Doctor of Biological Sciences Alexander Agadzhanyan, only three survived: placental, marsupial and oviparous. According to the studies of Academician Emilia Vorobyeva (Institute of Ecology and Evolution named after A. N. Severtsov of the Russian Academy of Sciences), carried out in the 1970s - 1990s, fish-like fish repeatedly tried to land on land. However, not only vertebrates are characterized by such "strivings". Various invertebrates tried to become arthropods (arthropods), which is reflected in the works of recent years by Alexander Ponomarenko, Doctor of Biological Sciences (A. A. Borisyak Paleontological Institute, Russian Academy of Sciences). And even in flora As shown in 1989 by another employee of ours, Doctor of Geological and Mineralogical Sciences Valentin Krasilov, there were at least six experiments to turn proangiosperms into flowering plants, most of which surround us today.
My colleague Ponomarenko figuratively called this picture of evolution an evolutionary "lawn". Many separate "stalks" develop on it simultaneously and parallel to each other. And we added that most of them "mow down" ecological and evolutionary mechanisms. And only some evolutionary "stalks", which are usually at the edge of the evolving space, are preserved, ripen, give a "whisk of seeds" and continue their further development.
But why, for example, did enantiornis go extinct, while real fan-tailed birds continued to develop? Perhaps because the enantiornis were in a hurry to become birds. We know the skeletons of their embryos from deposits of the Upper Cretaceous of Mongolia about 70 million years old. So, their skeleton was completely formed already in the egg. And their chicks, obviously, came out into the world as an absolute copy of adults. They only had to grow to their full size, and they grew all their subsequent life. In true fan-tailed birds, chicks, as in our time, hatched from eggs with a half cartilaginous skeleton. Then he very quickly, in the majority of 2 - 4 months, completely ossified and stopped further growth. Thus, enantiornis emerged from eggs as already formed birds and subsequently followed the bird's path, sometimes, probably, not reaching all the possibilities that flight provided them.
Real birds in the postembryonic period quickly reached the perfection of flyers, keeping it throughout their lives. Perhaps this was the main reason why the enantiornis lost the airspace to the fan-tailed? Recently, we described a unique find of a fossilized bird's brain from Cenomanian deposits (about 93 million years old) of the Volgograd region. A specialist in the study of the central nervous system of animals, Doctor of Biological Sciences Sergei Savelyev (Institute of Human Morphology, Russian Academy of Medical Sciences) believes that in this brain the departments responsible for mobility, intelligence, etc., were less developed than in modern birds. According to indirect evidence, such a brain could belong to enantiornis. Was this another reason for their competitive loss to real birds?
HOW DO THEY FLY?
Previously, it was believed that the origin of the feather and flight as such are inextricably linked. Now, after the discovery of various feathered theropod dinosaurs and various ancient birds, this hypothesis has to be abandoned. It turns out that the acquisition of feather cover was due to other circumstances.
Perhaps, at first, it had a heat-shielding function or covered its owners from the harsh ultraviolet sunlight. Short soft cover feathers cannot fly. Then where did the tough and long feathers of the wings and tail come from? It is assumed that the primary elongation and increase in their size in the ancestors of birds and flying dinosaurs was caused by the formation of decorating structures associated with mating demonstrations.
But how did they fly? Until now, two hypotheses have competed in this regard. One by one, "arboreal", denoted by the direction "from top to bottom", the first flights took place at the stage of arboreal archosauromorphic ancestors of birds, which climbed up the trees, clasping them with their forepaws, and then began to jump down, after which they flew. According to another, "ground", closely related to the origin of birds from dinosaurs, the vector was different - "bottom up": they ran and ran, faster and faster, jumped and finally flew. In any case, these were bipedal ancestors - bipedal, as we call them, moving only on hind legs, with free front limbs, freed from the function of support. But both hypotheses left many questions and inconsistencies that did not allow them to be accepted in their pure form. For example, in Archeopteryx, enantiornis, and Confuciusornis, the claws on the front legs (wings) are for some reason bent outward. How can you grip the barrel with this orientation? To do this, they must be bent inward in order to cling to the trunk.
Together with Igor Bogdanovich, Candidate of Biological Sciences (Institute of Zoology named after I.I.Shmalhausen, National Academy of Sciences of Ukraine), we have developed a new compromise hypothesis of the origin of flight. After bipedality, we consider the paw structure of birds and theropod dinosaurs to be the key factor. Already in the very first known Early Cretaceous true birds, the hind paw was arranged according to the anisodactyl type: its three front toes are directed forward, and the first inner paw is completely opposed to them and is aimed backward. By the way, although no one has yet found bird skeletons in the Triassic and Jurassic, prints of their footprints from the Late Triassic of Argentina and the Early Jurassic of Africa and Europe show just such a paw structure.
The sequence of hypothetical stages of acquisition of flight by real birds:
I - bipedal terrestrial arhosauromorph;
II - the emergence of anisodactyly in the archosauromorphic ancestor of true birds;
III - jumping onto the lower branches of trees and bushes;
IV - secure roosting with the final formation of anisodactyly and the initial reduction of the long tail;
V and VI - the appearance of feathers with symmetrical webs on the distal segments of the forelimbs and tail for mating demonstrations;
VII - the formation of asymmetric aerodynamic feathers on the wings and the reduction of the long tail;
VIII - transition to real flapping flight.
Further. In the earliest known real birds from the Lower Cretaceous sediments, the tail was already fan-shaped - a short spine with a short pygostyle (a row of fused last caudal vertebrae), on which feathers sat in a fan. What did it give them? With paws with such an arrangement of fingers, they could reliably grasp the branches and hold on to them, without balancing with a long tail. And gradually he disappeared, tk. there was no need for such a rear balancer, as it served Archeopteryx and feathered theropod dinosaurs. They could not hold firmly to the branches. Their first finger never reached a completely opposed position. Therefore, they had to stay on the branches, balancing with a long tail. And they could not climb the trees along the trunks, clasping them with their front paws-wings, since the claws on the fingers were bent outward. And what, then, did the claws oriented in this way serve? We suppose, in order to hold on to the surrounding branches with an unreliable support on their hind legs - after all, their fingers did not completely grasp the branch. Note: in the earliest true fan-tailed birds, although the claws on the toes were still preserved, they were already small and almost straight - not bent.
How, then, did these early birds and theropod dinosaurs, eager to fly, climb the trees? Probably jumping on the lower branches and moving higher and higher. Moreover, the former reliably held on to the branches with the help of their anisodactyl paws, while the latter helped themselves with long wing fingers with claws bent outward.
Why did they need trees for both? First of all, not to learn to fly. The flight began only later, as a result of the development of the above-ground level of life. It can be assumed that they began to climb there in an effort to develop new forage resources. Or get away from ground predators during overnight stays. Or to arrange nests there, thereby insuring their clutches of eggs and offspring, again from predators. Or for one, the other and the third together.
Having a short, lightweight tail and a light skeleton, real birds, initially descending from the trees, fluttering with the rudiments of feathered wings, eventually flew in a real flapping flight. Feathered dinosaurs, although they received long feathers on their wings, "grew" the same feathers on their hind legs, most likely they did not acquire real flight, although they became quite perfect "glider pilots".
So it remains to wait only for at least one find of a real bird with an anisodactyl paw, with a fan-shaped tail in the Jurassic, and even better in the Late Triassic sediments. And they were. It’s just that, for many reasons, we haven’t come across yet. Indeed, quite recently, we knew almost nothing about the Early Cretaceous stage in the history of birds. They didn't just not know. Some of the experts did not even believe that even then there were real fan-tailed.
The study was supported by the RFBR grant 07-04-00306.
Doctor of Biological Sciences Evgeny KUROCHKIN, Head of the Laboratory of the Paleontological Institute named after A. A. Borisyak RAS
Reading the article will take: 4 minutes"And why don't people fly like ... dinosaurs?" ©
For the first time, the thought of the giant-toothy origin of sparrows, ducks, geese and other feathered creatures visited me on Sunday morning - some kind of stomping creature galloped along the galvanized tide outside the window, commenting on its jumps with shouts on high notes. Slightly pushing the curtain aside, I discovered a bird of the starling system - and it was at this moment that the starling somehow reminded me of the Tyrannosaurus rex, popular among filmmakers. Yes, damn it - the same head turns, body swaying when walking, unpleasant cries! Could it really be that dinosaurs were among the ancestors of chilled chicken carcasses sold in retail chains?
Tyrannosaurus - a close relative of hummingbirds
The first thing that birds have in common with dinosaurs is the eggs that they carried in order to continue their offspring. However, the only group of more or less known flying dinosaurs - pterodactyls, which, judging by the images recreated by paleontologists, had absolutely no plumage ... 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 the school course in biology, Archeopteryx is considered the ancestor of modern birds - this creature really looked like a bird with its plumage and the structure of some bones. But according to the results of studies of recent decades, Archeopteryx was not a bird, to a greater extent it is a subspecies of dinosaurs, moreover, a dead end, i.e. not further developed and completely extinct millions of years ago. So who is he - the ancestor of the birds?
Paleontologists believe that birds evolved from the therapods - carnivorous dinosaurs with strong and long legs, short upper legs, a strong skull, sharp teeth and excellent appetite. The structure of the avian skeleton and the skeletons of dinosaurs of two families from the subclass of the therapods - oviraptosaurus and dromaeosaurids - is very similar. Moreover, representatives of several dinosaur genera belonging to the families mentioned were covered with feathers and had wings!
66 million years ago, at the very end of the Cretaceous period, there were dromaeosaurids. Strong, agile, about 180 cm tall and weighing about 15 kg, the dromaeosaurus was a successful hunter for live prey - long legs allowed him to accelerate to 80 km / h, jump at a distance of up to 7 m. Each leg had a long and sharp claw, with the help of which the dromaeosaurus pierced the skin of the victim in a jump, and also climbed trees to hunt from an ambush. Short wings did not allow him to fly - the dinosaur used them for braking when cornering. If you do not take into account the long tail and toothy mouth of the raptor, then in its size the dromaeosaurus resembled modern ostriches.
In the family of oviraptosaurs, paleontologists have discovered the largest representative of avian 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 do not end there - the gigantoraptor did not have the toothy mouth characteristic of dinosaurs, it had ... a bird's beak! Like the dromaeosaurs, the gigantoraptor used short wings to slow down on turns while chasing prey.
By the way, the largest dinosaur from the suborder of therapods, although it did not have wings, but was covered with the simplest 15 centimeters feathers, was the yutirannus - 3.5 meters high, 9 meters long and weighing one and a half tons. Yutyrannus lived at the beginning of the Cretaceous period, about 125 million years ago and belonged to the tyrannosaurus family - yes, those same tyrannosaurs!
Let's return to the oviraptosaurs, erroneously called by scientists "egg stealers", 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 did not know how to 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 Avimim, a small representative of the oviraptosaurus family - height no more than 70 centimeters, weight about 15 kg. This dinosaur could not fly because of the same short wings, but it ran perfectly, its beak was equipped with teeth, which allows scientists to consider the avimim carnivorous. 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 the first birds - protoavis, ichthyornis, enantiornis, etc., which feathered dinosaurs eaten with pleasure. As you know, the Cretaceous period ended with a sharp drop in temperature on our planet, which is why all representatives of 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 to rich areas, from cold to warm. Feathered land dinosaurs also tried to warm 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.
Paleontological materials on birds, as already indicated, are very scarce and fragmentary. Therefore, talking about the ancestors of birds among reptiles and about the origin and relationships of modern groups of birds has to be mostly presumably based on the morphological features of modern groups and, to a very small extent, on fragmentary paleontological data.
According to modern ideas, the ancestors of birds were the archosaurs Archosauria - a vast and very diverse group of reptiles that prevailed in the Mesozoic and included various dinosaurs, crocodiles, and flying dinosaurs. The immediate ancestors of birds, apparently, should be sought among the most ancient and primitive group of archosaurs - thecodonts or pseudo-aids Thecodontia (Pseudosuchia), which gave rise to the rest of the more highly organized groups of archosaurs. Pseudosuchia by appearance looked like lizards. They led a predominantly terrestrial way of life, apparently ate a variety of small animal food. The hind legs were somewhat longer than the front ones, and during a fast run the animals rested on the ground only with their hind legs. In many morphological features, pseudosuchies are very similar to birds (details of the structure of the skull, pelvis, hind limbs). Intermediate forms that would make it possible to find out the stages of plumage development and the development of the ability to fly have not yet been found. It is believed that the transition to an arboreal lifestyle and adaptation to jumping from branch to branch was accompanied by the growth and complication of the structure of horny scales on the sides of the body and tail, along the posterior edge of the fore and hind limbs, which provided the possibility of planning and lengthening jumps (hypothetical stage of the forebird, according to Heilmann, 1926, fig. 13).
Further specialization and selection led to the development of the wing feathers, which provided the possibility of first gliding and then active flight. The plumage, covering the entire body of birds, probably developed not so much as an adaptation for flight (providing streamlining of the body), but as an adaptation for thermal insulation; it is suggested that it could have formed even before the development of the ability to fly. Some pseudosuchia had elongated horny scales with a distinct longitudinal ridge, from which small transverse ribs extended. Such scales, apparently, can be considered as a structure from which a bird's feather could arise by dismemberment.
The separation of birds from reptiles, apparently, took place at the end of the Triassic - early Jurassic (170 - 190 million years ago). However, the fossil remains of birds from this time have not yet been found. Fairly good remains of the two oldest birds known to us were found in the 1860s. near Zolengofen (Bavaria) on the development of shale sandstones, representing the deposits of the shallow bay of the Jurassic Sea (age about 150 million years). They were named Archeopteryx lithographica and Archaeornis simetisi... In 1956, in the same place (within a radius of up to 300 g, but at a different depth), a significantly worse preserved imprint of another individual was found. Some researchers regard these findings as the remains of three different types(two species of the genus Archeopteryx and one of the genus Archaeornis), while others are considered representatives of the same species Archeopteryx lithographica explaining the differences between individuals as individual, age and sex. This question needs additional study, but even now it is quite obvious that all these individuals are very close. All of them have a well-developed plumage of the wings, tail and body, some proportions of the skull are closer to the avian than to the reptilian, the avian features are the belt of the forelimbs and the pelvis, hind limbs... Typically reptilian features: there is no horny beak, there are weak teeth, the hand carries the primary flight feathers, but the buckle has not yet formed and there are three well-developed movable fingers with large claws, the formation of a complex sacrum has just begun (the vertebrae are not yet fused, the movable bones are connected with a small number vertebrae), the thigh joins at an obtuse angle (directed somewhat sideways), the proximal tarsal bones have not yet grown to the end of the tibia, the fibula is well developed, the formation of the tarsus is not complete, etc. morphological features and, as far as it can be assumed now, the way of life is archepteryx (and archeornis) - ancient, primitive, but birds.
The subclass of real, or fan-tailed, Neornithes birds, apparently, are direct descendants of some Archaeornithes lizard-tailed birds. Some researchers (for example, Gadov) consider Archeopteryx and Archeornis to be the direct ancestors of birds, while others (perhaps the majority of them) consider the Archeopteryx group as a primitive, but specialized lateral and blind branch, believing that the ancestors of modern birds should be others, not yet discovered lizard-tailed birds (if found, they are likely to form another order of this subclass).
The origin and relationships of modern groups (orders) of birds remain, as already mentioned, in the absence of sufficient paleontological materials, as a rule, very hypothetical. M. Furbringer paid the most attention to this issue, and G. Gadov paid much less attention. Not much that is new and indisputable has been introduced into this problem by modern authors who, to one degree or another, concerned the phylogeny of birds. Therefore, here is presented an idea of the relationship of individual groups of birds, mainly according to Fürbringer, but in a number of cases, where it is necessary, some changes were made (in some cases, these changes are not specifically mentioned).
Fossil remains of fan-tailed birds were found only in the Cretaceous period (their age is approximately 80 - 90 million years), that is, they are several tens of millions of years younger than Archeopteryx. According to several poorly preserved remains, hesperornis are described - very large (more than 100 cm long) birds, apparently, apparently somewhat similar to loons or grebes, did not fly at all (the sternum without a keel, only a small thin shoulder was preserved from the forelimb), but probably , they swam and dived well: their jaws carried their teeth. In the Cretaceous sediments, the remains of other toothed birds - ichthyornis were found. They had a well-developed sternum keel, a typical bird's wing, and, apparently, had an active flight. They were about the size of a pigeon. The relationship of toothy chalk birds with other birds is very unclear. Perhaps some of these remains belong to the Cretaceous dinosaurs, and not birds, but some are undoubtedly toothy birds. Fürbringer brought Hesperornis closer to loons and grebes, and their Thiornis to seagulls, but at the same time emphasized their very old isolation.
Gadov hesperornis singled out in a superorder, showing by this their isolated position, and ichthyornis, as an independent order (also separate), began the list of orders of keeled birds. Emphasizing the ambiguity of the origin (and the volume) of these groups, Wetmore (1960) distinguishes them into independent superorders.
Several more families of birds have been described from the Cretaceous deposits (from fragments of jaws and tubular bones), but their position and appearance are very unclear: perhaps at least some of these finds are the remains of reptiles. The remains of birds found in the sediments of the Tertiary period of the Cenozoic era (less than 55 million years old) are more or less likely to be attributed to modern orders. In any case, they belong to typical birds, close to one or another group of modern birds. Judging by these materials, it can be assumed that the intense adaptive radiation of birds and the formation of most modern orders took place at the very end of the Cretaceous period of the Mesozoic era - in the Tertiary period of the Cenozoic era, i.e., in the period about 70-40 million years ago.
The reptiles of all living and fossil large flightless ostrich-like birds were singled out into the superorder of ratites, thus emphasizing their similarity and phylogenetic relationship (i.e., monophilia), as well as their certain isolation from other groups of birds. Among keel birds the closest to ostrich-like tinam (hidden tails) are chickens, cranes and similar groups. Fürbringer and most modern authors (Wetmore, Stresemann, etc.) consider ostrich-like birds to be a combined polyphyletic group, divided into a number of independent units that start the system, which implies their certain primitiveness and isolation. Their common similarities are the result of convergence: large size, loss of ability to fly, adaptation to fast running, etc.
According to Gadov, the evolution of the rest of the birds went in two directions (two branches, see above), each of which, in turn, is divided into 2 groups of related orders. Grebe-loons (ichthyornis, grebes, loons, penguins and tube-nosed) are related to the Pelargomorphae group (storks, anseriformes, predators), and a group of chickens (tinamu, chicken, crane-like, ...
Fürbringer's evolutionary ideas are in general terms close to this scheme of Gadov (other views on ostrich-like species were discussed above), but he expounds his ideas with a greater degree of detail. The large trunk of birds - the order Pelargornithes - is divided into a number of branches: anseriformes, grebes (including grebes, loons, hesperornis); from the base of these branches another powerful branch departs, which, dividing, gives rise to copepods, diurnal predators and groups of the suborder storks (Fig. 14).
The order Palamedei Palamedeiformes occupies an intermediate position between the rhea and the order Pelargornithes. Intermediate orders of penguins Aptenodytiformes and tube-nosed Procellariiformes are rather isolated; perhaps they have long-standing weak ties with each other and, even more distantly, with the orders of the Pelargornithes and the Sandpiper Charadriornithes. Ichthyornis Ichthyornithiformes are also an intermediate order, but with somewhat more pronounced long-standing connections with sandpipers. The order of Sandpipers Charadriornithes, with very long-standing ties, apparently can be close to the order of Raksha-like. The main trunk branching of sandpipers is the suborder Laro-Limicolae - sandpipers, gulls and guillemots; goat runners and bustards are quite close to them (bucksmiths serve as a transitional group between waders and bustards). Two more large branches separated from the base of the sandpiper's trunk: the crane-like Gruiformes and the shepherd's Ralliformes. Cranes are divided into several branches: the actual cranes (cranes, aramids, trumpeters, kariams) and the sun herons and kagu, which occupy a somewhat isolated position. Shepherds are subdivided into related branches: shepherdesses, foot-footed and standing somewhat apart three-fingers and Madagascar shepherdesses.
One of the ancient trunks of the family tree of birds is the order of the chickens Alectorornithis. The most primitive branch is the Apterygiformes suborder wingless, or kiwi, which includes kiwi and moa; both groups dispersed almost immediately after their separation. The common origin with the previous branch, apparently, is related to the tinamu (or hidden tails) Crypturiformes, in turn, through ancestors close to the suborder of chickens Galliformes (almost to the modern extent). The order of chickens with very long family ties, probably more or less close to the shepherd Ralliformes, and through them to the entire order of the sandpipers.
Intermediate orders of dove-like Columbiformes (including sandgrouses and pigeons) and Psittaciformes parrots occupy a separate position in the system. Probably, through a very long-standing relationship, they are somehow connected with the vast detachment of Raksha-like. According to Gadov's ideas, pigeons and sand grouses in the rank of suborders are included in the order of sandpipers, and parrots - also as a suborder - in the order of cuckoo-like. In fact, Wetmore adheres to a similar point of view, placing a detachment of pigeons immediately behind a detachment of sandpipers, and a detachment of parrots next to a detachment of cuckoos.
The vast and varied order Coracornithes is associated with the ancestors of the order of sandpipers. The main and most powerful branch is the suborder of woodpeckers and passerines Pico - Passeriformes, which is then divided into separate groups of actually passerines and woodpeckers. Macrochires (swifts, hummingbirds) and Colii mouse birds have separated from the base of this branch. Even earlier, the trogons Thogones separated from this branch. From the very base of the branch of woodpecker-passerine birds, three other suborders of rakshiformes also separate. The suborder of cuckoo-like Coccygiformes separates the branch of the yakamar Galbulae (yakamars and puffs, and according to Wetmore it is a suborder of the order of woodpeckers), and then divides into the cuckoos Cuculidae and bananoids Musophagidae. The suborder of rakshiformes Soraciiformes is divided into the raksh Coraciae proper and into a second branch, which soon divides into owls Striges and nightjars Caprimulgi. The suborder Halcyoniformes kingfishers (it is, apparently, closer to Pico - Passeriformes than to other suborders), separating at the very beginning the lateral branch of Todi Todi (except Todi Fürbringer, this includes Momots), is divided into 3 related groups: Halcyones (Alcedinidae ), hoopoe Bucero tes (hoopoe, hornbill) and bee-eaters Meropes.
Comparison of Fürbringer's phylogenetic concepts with the views of Gadov and Wetmore (the order and order of listing the orders) shows their significant coincidence; the sharp differences in the position and relationship of individual groups are indicated above.
V last years an attempt to graphically depict phylogenetic relationships between individual groups of birds was undertaken by the German ornithologists Berndt and Meise in the three-volume capital summary "Natural history of birds" (Bernd R., Meise W. Naturgeschichte der Vogel, Kosmos, Stuttgart, 1960 (1962), v. 2, p. 668 - 673). The subclass of ancient lizard-tailed birds Palaeornithes gave rise to the subclass of new fan-tailed birds Neornithes, which includes 24 orders, usually subdivided by the authors directly into families; taxonomic categories of the rank of the suborder and superfamily are used, as a rule, only in the order of passerines. The relationship between the orders of birds, according to Berndt and Meise, is as follows:
From ancient birds, evolution proceeded in two directions (branches): branches (superorder) of terrestrial and aquatic birds Geornithes and branches (superorder) of arboreal birds Dendrornithes. From the very beginning, the branches of terrestrial and aquatic birds (Fig. 15) separated by a common trunk, later separated, the Crypturi tinamu and the ratite birds Ratitae, including all living ostrich-like birds, including kiwi, and fossils of moa and epyornis. Further, the Galli chicken birds (in the full volume of Wetmore's detachment) stand out and at the same level, but an independent branch - the loons-like Pygopodes (including the fossil chalk-toothed birds of hesperornis, loons and toadstools). All other units of this branch (superorder) have common origin- they are like a whorl of trunks extending from one site. Crane-like orders (shepherdesses, Madagascar shepherds, sun herons, Poinfoots, kagu, real cranes, aram, trumpeters, bustards, karyams, three-fingers) are relatively closely related to other groups; from fossils - diatrims and fororaks Phororhacidae and wading and gull-like birds Limicolae - Lari (yakans, various groups of sandpipers proper, guillemot gulls and - from fossils - toothy chalk birds - ichthyornis). Further, from the common base of the whorl (i.e., having common ancestors), the orders of Anseriforms (Palamedeans and Anseriformes proper), Flamingos Phoenicopteri, Ankle Gressores, diurnal predators Accipitres, and Copepods Steganopodes are successively separated. From the forms close to the ancestors of the copepods, a branch is separated, which then divides into the orders of the tube-nosed Tubinares and the penguins Sphenisci.
The development of the second branch (superorder) of the arboreal birds Dendrornithes begins from some ancestral forms, apparently more ancient than the ancestors of the first branch (the first superorder). At first, 3 orders are separated by a common trunk: the cuckoo-like Cuculi, the Columbae pigeons (doves, sand grouses and dodos) and the Psittaci parrots. The next isolated branch is divided into 2 branches, each of which forms 2 detachments. One of them gives rise to the Striges owls and the Caprimulgi nightjars, the other to the Trogones trogons and the Coracii rakshaki. Further from the common trunk, the orders of bird-mice Colii and swift-like Macrochires (swifts and hummingbirds) are also separated by a common branch, the detachment of woodpeckers Pici (in Wetmore's volume) departs as an independent branch, and the main trunk branches into numerous units of the order Passeres. In addition, the authors provide hypothetical schemes in which they try to represent phylogenetic relationships within several separate orders (diurnal predators, copepods, loons, and passerines).
The phylogenetic schemes of Berndt and Meise are clear, visual and easy to remember. However, they are practically not at all reasoned, not substantiated by materials and, apparently, to a much lesser extent reflect the actual kinship (phylogenetic) relations between individual groups of birds than the corresponding schemes of Fürbringer. It is theoretically unlikely that the subsequent biotopic specialization of birds was clearly defined already at the initial stages of the evolution of the class, which is expressed in the outlined scheme of dividing the subclass of "new birds" into only 2 separate superorders and in an almost linear, sequential separation of orders. Estimating the nature of evolution inherent in birds by modern forms, which is expressed in a wide adaptive radiation within individual groups (which was briefly mentioned above), it seems more logical to assume that a similar wide adaptive radiation was characteristic of the initial phases of the evolution of the class. If this is so, then we can say that Fürbringer's phylogenetic schemes, at least outwardly, really reflect the predominance of this type of evolution.
It is still too early to talk about a fully developed class system. However, the systems of Fürbringer, Gadow and Wetmore, apparently, can be considered as a good basis for constructing natural system... Their materials give the most general idea about phylogenetic relationships of most groups. To improve and clarify the system of the class of birds, further various studies are required at all taxonomic levels (from subspecies groupings to orders and superorders): morphological, ecological, ethological, and genetic. Perhaps, in the future, valuable materials will be provided by the use of biochemical and physiological indicators; usage modern techniques has not made a significant contribution to the taxonomy of birds so far. Hopefully, the number of paleontological materials will also increase, which will make it possible to more reasonably discuss the evolution of birds in general and of individual groups (orders, families).
All the features of birds that distinguish them from reptiles are predominantly adaptive to flight. Therefore, it is natural to think that birds are descended from reptiles.
Birds descend from the most ancient reptiles, in which the hind limbs were built in the same way as in birds. Transitional forms - Archeopteryx and Archeornis - in the form of fossil remains (imprints) were found in the Upper Jurassic deposits. Along with the features typical for reptiles, they have signs of the structure of birds.
Adaptation of birds to their habitat
Birds have adapted well to a variety of living conditions: to life in swamps, aquatic life, in the air, forests and shrubs, plains or rocks.
For some birds (swifts, swallows, etc.), air is the main habitat, since they feed on various flying insects in the air. Birds that forage in the air are inhabitants of cliffs, rocks and woody vegetation. Swallows and swifts, for example, adapted for the second time to build their nests in human buildings, replacing the slopes of the banks and rocks.
Those birds that use air both as a medium of movement and as a medium for obtaining food spend most of the day in flight. They have the most advanced aircraft.
Small and medium-sized birds (swifts, swallows, falcons) have an extremely elongated wing, pointed towards the top. Their tail is often deeply cut, or forked. These birds fly very fast and can make unexpected turns. In larger bird species, the aircraft is adapted to hover. For example, in marine forms (gulls, petrels), the wing is relatively long and narrow, while in land forms (birds of prey) it is wider and shorter.
Birds that use water as a habitat and prey for food also have appropriate adaptations. They walked in two directions: the attachments of the wings and the attachments of the legs.
Some birds (petrels) have extremely long wings and hover over the water all day long and grab the food they see. Such birds can swim on water. Other birds (penguins) use wings to move in the water, which act as oars. The feathers of the penguin's wing have turned into scale-like formations, so these birds cannot fly at all.
In those aquatic birds that use their legs for swimming and diving, in the course of evolution, membranes have appeared between the toes. An exception is the water chicken, which swims well and has no membranes on its legs.
About 150 million years ago (in the middle of the Jurassic period), a branch deviated from the reptiles, which laid the foundation for the birds.
A little later, mammals (animals) also originated from other branches of reptiles, although their ancestors - animal lizardmen - arose earlier than the ancestors of birds. Now, one can quite accurately imagine how this development took place. In the ground, in layered shales Western Europe(GDR, FRG and other places) found fossilized remains of skulls, bones of ancient birds and their ancestors, whole skeletons with scales, imprints of feathers and the entire wing.
How did this happen?
Some lizards began to run away in fear and danger. At the same time, they climbed onto their hind limbs (there are such lizards now). Then they learned to run only on their hind legs (which took millions of years). Calculations and comparisons give us the right to assert that they already had a four-chambered heart, since the ancestors of crocodiles, who have the same heart, were close to this family (pseudo-ear). It was an aromorphosis, an evolution that brought about a sharp rise in their entire organization.
The running lizards made leaps and their front limbs acted on the beta like rudders. Their horny scales began to elongate, forming combs along the edge from the hand to the elbow, scooping up more air while running. Further. These running species gradually moved on to climbing rocks and trees. For prey, they began to climb branches, which is what modern chameleons and many iguanas do.
Among the fossil lizards, some species had hollow skeletal bones filled with air. Trees were climbed both by those with such bones and those with heavy bones. But when it was necessary to jump from branch to branch, and later from tree to tree, the light-boned lizards jumped further and did not break when they fell. Soon (relatively) their scales and on the sides of the body began to lengthen, as well as along the hind edge of the forepaws. The scales lengthened and split, it was very light and "scooped up" more air during the jump, keeping the body in flight. It was easier for such an animal to jump - its body was flattened. Recall that a sheet of paper falls slowly, and if crumpled, it falls much faster. The scales stretched out in all directions acted like a parachute. Each flake was split in different ways: "herringbone" along the edges from the thickened middle rod or along the radii, to one center. In the first case, a feather was obtained from the scales, and in the second - fluff. In other parts of the body, the scales remained unchanged for a long time (for example, on the legs, the horny cover of the beak).
Ancient lizards, with still underdeveloped feathers, climbed trees and rocks using all four limbs, which had fingers and claws. Only on the forelegs were wide feathery scales, which formed flat visors along the hind edge of the paw. Such animals (pseudosuchies) are also known in the fossil state. It was they who gradually turned into first birds (Archeopteryx). Their skeletons with fingerprints and even feathers have been preserved quite well. In 1974 in Bavaria (FRG), in the quarries of Zolengofen, a well-preserved skeleton of the fourth Archeopteryx, the size of a starling, was found. The previous three finds were about the size of a pigeon. It was proven that the bones were hollow, like real birds. Consequently, air sacs extending from the lungs entered the bones. They had similarities with both lizards and birds.
Let's give the following comparison:
Signs of reptiles preserved in the first birds:
- The jaws, although narrow, do not form a beak
- On the jaws - teeth
- Tail of 21-28 vertebrae (could be bent)
- On the front legs - three free fingers
- The ribs were attached to the vertebrae, like in lizards, at one point and did not have processes facing backwards and extending into the next rib in birds.
"Bird" signs of reptiles:
- The body is covered with feathers.
- Bones (thighs and humerus) are hollow. Hence, there were air sacs entering the bones.
- The shoulder and forearm became a wing.
- On the wing, dense feathers grew, overlapping edges of each other, like real birds.
- Below the tibia, from the longitudinally fused bones, a tarsus was formed.
To this we add that air sacs are moving away from the lungs of modern chameleons. Some dinosaurs also had cavities in their bones. However, neither one nor the other have flown and do not fly. Therefore, it is not necessary to say that these devices served to "facilitate" the flight. Moreover, the best modern flyers - swifts have no hollow bones. They are "overgrown" with bone marrow.
So, the jaws of the first birds were still wide, with many small teeth. Long, like that of lizards, the tail consisted of many vertebrae and could bend in all directions. On the forelimbs, at least two fingers had disappeared, the remaining three were still well developed, with claws and, apparently, helped with lasagna. But behind the hand, the limb was already carrying a fairly well-developed wing of dense feathers. Such pioneers, probably, still did not fly well, they could only flip from tree to tree. The tail was the first to be shortened. The long tail outweighed at. planning, although it was cased along the edges with feathers. Then the forelimbs, which worked both as a climbing paw and as a wing, were gradually released from the previous load and began to work only as a wing, having lost free toes.
There are, however, and in our days birds that keep free fingers on the wing, even with claws. Hoatzin chicks climb the branches in this way. The claw on the first toe is found in certain carnivorous species, geese, and Haun's palameds. In other palameds, "spurs" protrude from the edge of the wing, undoubtedly of the same origin. On the second toe, claws are less common in modern birds. They are known among the cassowary rhea, kiwi and toucans. Finally, in the African ostrich, claws grow on all three toes of the wing.
The teeth of the first birds were still preserved for a long time: judging by the skulls from the later layers of the earth (Cretaceous period), for 50 million years. The teeth disappeared completely from birds about 70 million years ago. The remains of the fingers in the wing have been preserved in all birds to this day. There are three of them, including a short front ("thumb"), which can still turn slightly. A separate bundle of feathers is attached to it - a “winglet” at the front edge of the wing. Fast flying (predatory, etc.) birds, turning their wings, regulate flight, slow down on the fly, etc. On the legs of the birds, scales from ancient ancestors - lizards - are preserved. The structure of eggs and the development of bird embryos is very little different from the development of lizards. Body temperature became constant. The changed circulatory system with a four-chambered heart provides more active blood oxidation (connection with oxygen), which increases the body temperature, and a thick cover of feathers and down keeps warm.
So the climbing lizards, who learned to jump, and later jump from tree to tree, later became birds.
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