Are birds descendants of dinosaurs? These amazing ancient birds.

Everyone has long known that birds evolved from dinosaurs, but few people know about ancient birds. mesozoic era who lived side by side with giant reptiles, or cenozoic era- the space of geological time after the extinction of the dinosaurs. The following 10 paragraphs of the article provide a description and photos of extinct species prehistoric birds(in chronological order their appearance), which had a decisive influence on the evolutionary development of feathered animals.

1. Aurornis (160 million years ago)

Perhaps someone thought that the first on the list should be Archeopteryx, but small birds of the genus aurornis appeared before Archeopteryx by 10 million years. However, aurornis had more in common with dinosaurs than with birds, and its feathers were too thin to be useful in flight. However, we will consider aurornis the most ancient bird, and we will leave disputes with reflections to paleontologists.

2. Confuciusornis (130 million years ago)

Unlike the previous representative of fossil birds, Confuciusornis were more like modern birds. These were the first birds to have a genuine beak. They had no teeth (the main feature of reptiles), the body was covered with a thick layer of feathers, and long, curved claws made it possible to sit confidently on the branches. tall trees. Despite the foregoing, it cannot be definitively concluded that all modern birds are descended from Confuciusornis: it is likely that birds appeared and died out independently of each other several times during the Mesozoic era.

3. Gansus (110 million years ago)

As you already understood from the first paragraphs, it is very difficult (or even impossible) to fully understand the evolution of birds that lived tens of millions of years ago. Gansus- another species of prehistoric birds, which is presented in paleontological circles as the oldest representative of the subclass of true birds (that is, the direct ancestor of all modern birds). This theory causes a lot of controversy, but still, long extinct gansus the best contender as the progenitor of modern ducks and loons.

4. Hesperornis (75 million years ago)

Ancient birds had enough time to develop and de-evolve in the second half of the Mesozoic era. What is fascinating is the fact that birds of the genus Hesperornis were secondary flying birds (that is, they evolved from early flying birds, but gradually lost the ability to fly like a penguin or a turkey). Perhaps this happened due to competition with large pterosaurs of the late Cretaceous North America, in particular the ubiquitous pteranodons, so that the Hesperornis had to be content with a terrestrial ecological niche.

5. Gastornis (55 million years ago)

After the death of dinosaurs, about 65 million years ago, birds were able to develop in the vacant ecological niches. The role of a frightening bipedal predator passed to 2 meter birds from the genus Gastornis (also known as diatryms). It is assumed that the Gastornis hunted in packs, chasing their victims like smaller copies of the Tyrannosaurus rex.

6. Eocypselus (50 million years ago)

Have you ever wondered what it looked like prehistoric ancestor hummingbird? Paleontologists do not particularly cover this, but it has long been known that hummingbirds originated from eocypselus- a species of small birds living in the forest area of ​​the early Eocene of North America, about 50 million years ago. Wings eocypselus were larger than those of a modern hummingbird, so its flight could not be called graceful.

7. Icadyptes salasi - the ancestor of penguins (40 million years ago)

It can be assumed that the ancient penguins, who lived about 40 million years ago, had the same lifestyle as modern ones: they lived on ice floes, dived for fish and cleaned their feathers at every opportunity. To a large extent, this assumption is true, with the exception of life on ice. At the end of the Eocene icadyptes actually lived in tropical climate near the equator South America. These penguins were larger than modern species and reached 1.5 m in height and weighed about 35 kg.

8. Fororacos (12 million years ago)

Remember the Gastornis (see point 6), 2m tall and weighing over 100kg, that lived ten million years after the dinosaurs? So, after 40 million years, fororakos became a worthy replacement for gastornis. To a large extent, the Phororacos led the same way of life as the Gastornis. Although, they had an additional weapon in their arsenal: a long, ax-like beak that they used to inflict deep, fatal wounds on their victims.

9. Argentavis (6 million years ago)

As impressive as birds looked during the Cenozoic era, they never matched the size and grandeur of the largest pterosaurs. At the end of the Miocene era, Argentavis was the largest flying bird, with a wingspan of up to 7 m and a mass of 70-72 kg. Impressive? But, 60 million years before that, the pterosaur Quetzalcoatl had a wingspan of about 12 m (like that of a private jet). Oddly enough, the smaller Argentavis flew like pterosaurs, also hovering on air currents rather than actively flapping its wings.

10. Epiornisidae (2 million years ago)

The Pleistocene epoch, from 2 million to 10 thousand years ago, was the period of the return of the megafauna. In addition to saber-toothed tigers and mammoths, the Pleistocene produced giant birds such as the Madagascar epiornis from the epiornis family. In height, these birds reached 3-5 m and had a body weight of up to 500 kg, and their eggs were approximately 100 times the volume of a standard chicken egg.

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praporweg September 7, 2015 at 04:55 pm

Comparative physiology of dinosaurs and birds. Popular about the unknown. Part 1 "Bones of the Titans"

• Popular science

In one of mine, you got acquainted with the chronology of the largest geological and space disasters in the history of our planet. The last of the 5 largest "apocalypses", supposedly put an end to more than 150 million years of the existence of the "kings" of the Mesozoic era fauna - dinosaurs. However, the “terrible lizards” nevertheless left behind paleontological “traces” that allow us to get acquainted in detail with the difficult life of these reptiles.

In several parts of this voluminous review, I will try to give you little-known details about the physiology and life of the ancient giant (and not so) "terrible" reptiles. Below in common features ah will be described Comparative characteristics skeleton, intelligence and genetics of dinosaurs with those of their modern descendants - birds, and related crocodiles.

"Dissimilar Relatives"

In general, a huge difference is recorded in the structure of the skeleton of modern birds and dinosaurs, this is explained by 160 million years of adaptation of a certain group of maniraptors to active flight, which caused a cardinal "restructuring" of the skeleton and physiology of birds. Something similar is observed in mammals when comparing ungulates and their marine relatives (cetaceans).
Such acquisition of significant differences in the morphology of related animals during their adaptation to different ecological niches in science is called divergence.

Who is relative to whom? Systematics predatory dinosaurs and birds

Maniraptors are a large group of dinosaurs, including both modern birds and their close relatives - deinonychosaurs (small predators with a "terrible claw"). Deinonychosaurs themselves were divided into troodontids (by the name of the known kind- Troodon, who lived at the end of the dinosaur era), and dromaeosaurs (eg Bambiraptor and Deinonychus). In turn, maniraptors, along with tyrannosaurids and ornithomimosaurs ("bird mimics"), were part of an even larger group of tyrannoraptors. The latter, together with comsognathae (small predatory theropods), formed the most numerous group of theropods - cellurosaurs.

The most studied representatives of the family of deinonychosaurs, the feather cover is supposed to be based on the traces of "feather" cells preserved on the wing-like hands of Velociraptor and Deinonychus

However, cellurosaurs do not cover all known theropod predators. The Jurassic (and early Cretaceous) period was dominated mainly by carnosaurs, which diverged (genetically) from cellurosaurs c. 170 million years ago, and with which they are included in the giant infraorder tetanurs. Of the most significant carnosaurs, carcharadontosaurus, giganotosaurus, and allosaurids should be noted. Spinosaurus, the largest predatory theropod of the era of dinosaurs, was also part of the titanur group, but as a representative of a separate order of spinosaurids from cellurosaurs.

Relative sizes of the largest carnivorous theropods

In addition to tetanurs, other groups of predators are also known. One of the main "villains" of the video game "Turk" - carnotaurus, belonged to the infraorder of ceratosaurids, relatively primitive small predatory dinosaurs.

In general terms, the morphology of dinosaurs was a cross between the archaic features of reptiles (bone structure, genetics and metabolism) and the progressive features of birds and mammals (upright walking, feather cover, structure of the jaw apparatus of herbivorous dinosaurs). The dominance of certain (progressive or archaic) traits most likely varied greatly among different orders and even families of dinosaurs.

All dinosaurs are divided into two main groups - lizards and ornithischians:

In bipedal lizard dinosaurs - theropods (diagram below), the center of gravity was located on the line of the pelvis, a heavy tail balanced the massive head of the animal. The pubic (red) and ischium (green) pelvic bones were located perpendicular to the spine along the hind limbs of the animal. The ilium is highlighted in blue, on which the thigh muscles are attached (including in humans).

Tyrannosaurus rex, a typical saurischian predatory theropod related to birds in the cellurosaur group

The hip joint of the main part of the "four-legged" herbivorous dinosaurs differed significantly from that of theropods. In particular, the pubis and ischium were located behind the pelvis of animals parallel to each other (similar to birds, the so-called "ornithischian dinosaurs"). However, such a division into "two-legged" and "four-legged" is very arbitrary, since four-legged sauropods had a hip joint similar to theropods, and many ornithischian dinosaurs actively practiced locomotion on their hind limbs.

Ornithischian dinosaur of the hadrosaur family ("duck-billed" dinosaurs)

Sauropod from the genus Brachiosaurus, it can be noted that it belongs to the lizard dinosaurs, despite moving on four limbs

The hip joint of birds is much less mobile, the pubic and ischial bones are directed backward and fused with each other and often with the back of the pelvis and caudal vertebrae, forming a complex sacrum. The tail of birds is strongly reduced to a pygostyle (which was also present in some oviraptosaurs), the spine is inactive. The ribs of birds have hooked processes that allow the thoracic region of the animal not to move during flight. At the ends of the ribs of most birds, the sternum and keel are attached, which in turn are attached to the strong flywheel muscles of the wings. The ribs and spine of dinosaurs were more mobile than those of birds, they also did not have a keel (however, modern non-flying birds such as ostriches do not have it either).

Separately, the different structure of the cervical vertebrae of birds and dinosaurs should be mentioned. In the latter, they are amphicoelous (biconcave) or procoelous/opisthocoelous (concave on one side and convex on the other, like in most reptiles). Cervical vertebrae in birds are heterocoelous - saddle-shaped, convex-concave on both sides, which provides them with great mobility of the cervical region, inaccessible to any known species of dinosaurs and mammals.

Skeleton of a modern bird (pigeon)
1 - skull, 2 - cervical vertebrae, 3 - fork, 4 - coracoid process, 5 - uncinate processes of the ribs, 6 - keel, 7 - patella, 8 - tarsus, 9 - fingers, 10 - tibia (tibiotarsus), 11 - fibula (tibiotarsus) 12 - thigh, 13 - ischium, 14 - pubic bone, 15 - ilium, 16 - tail vertebrae 17 - pygostyle, 18 - compound sacrum, 19 - scapula, 20 - lumbar vertebrae, 21 - humerus, 22 - ulna, 23 - radius, 24 - wrists, 25 - hand, 26 - fingers, 27 - wing

The femurs of birds, even those that do not fly, are inactive and point away from each other. Land birds move mainly with the help of the movement of the tibiotarsus (the lower leg of a bird with an adherent fibula) and the tarsus (fused bones of the metatarsus). Those. the tibiotarsus of birds, mechanically, plays the role of the femur in mammals and dinosaurs. Dinosaur limbs, on the contrary, were located parallel to each other and under the body of animals, in contrast to other reptiles and similarly to modern mammals. Obviously dinosaurs were not reptiles in the literal sense of the word. The dinosaur tibia, like the mammalian tibia, consisted of two tibia bones, many (especially small dinosaurs) did not have a tarsus, and similarly to humans, they had non-fused metatarsal bones.

From left to right, a comparison of the hind limbs of a theropod family of tyrannosaurids (rex species), wolf mammals (foxes) and land birds (ostriches). 1 - thigh bone, 2 - lower leg bones (tibia and tibialis / tibiarzus in birds), 3 - metatarsus bones, fused into the tarsus in birds (with the exception of penguins) and some dinosaurs - theropods. Green color indicates the bones actively involved in the movement of the animal. Roughly speaking, the role of the knee in modern birds is played by the ankle joint.

Running simulation of dinosaurs (Gallimimus and Tyrannosaurus rex) from Jurassic Park compared to modern ostrich running (bottom)

The sedentary hips of birds allow them to actively move along the ground, without risking the collapse of the air sacs necessary for active breathing (in flight and running, the lungs of birds do not expand like those of mammals, the same air sacs “pump” air through them). Some paleontologists accept this fact as indirect evidence of a different theropod respiratory system than an avian one.

The discovery of an aerosteon, a predatory theropod of the carnosaur group that lived 80 mya, partly refutes the conclusions above. The "air bones" of the dinosaur supposedly bear traces of the presence of air sacs. Initially, such bags could serve for thermoregulation of dinosaurs, and only then, with the improvement of metabolism, they began to be used for intensive gas exchange.

The differences between the two groups of animals become even more pronounced in a comparative analysis of their skulls. The skull of a bird is attached to the cervical vertebrae from below, while the cervical vertebrae of dinosaurs were attached to the back of the skull. The skull of birds has a spherical shape and has two diapsid arches, the upper of which is strongly reduced. The dinosaur skull is less spherical and has two developed diapsid arches (most often with temporal fenestrae). The jaws of dinosaurs are complex, and like mammals are filled with teeth. Modern birds have no teeth, and instead of a complex jaw apparatus, they have a relatively simple, light, but strong beak.

Reservation. The last comparison is not entirely correct, since scientists know both “toothless” dinosaurs (oviraptors) and “toothy” birds (enanciornis birds that dominated the Cretaceous period had a dinosaur-like jaw apparatus.)

Graphical representation of the evolution of progressive dinosaur traits from "terrible lizards" to "terrible birds"

(Time scales and order of appearance of animals are not respected)

Tyrannosaurus Rex, who lived 70-65 million years ago, was a very typical (if not standard) theropod. Of the typical features of a dinosaur, two powerful hind limbs, a lizard-like hip joint, and a massive tail, which serves as a balance for the large and overweight head of the animal, catch the eye. The skull is attached to the cervical vertebrae at the back, there are powerful jaws covered with teeth, preorbital foramina (lightening the skull) and for the orbital diapsid foramina where the jaw muscles of the animal (an analogue of the human temporal cavity) were attached. Against the background of closer relatives of birds - dromaeosaurs, it is distinguished by the absence of a furcula (fused bones of the clavicle) and greatly reduced relative sizes of the forelimbs

Deinonychus, who lived 40 million years earlier than Tyrannosaurus rex, had such bird-like features of his skeleton (in life, the animal was the size of a wolf), which served for paleontologists (features for the famous John Ostrom), one of the first convincing evidence of the origin of birds from dinosaurs . In particular, the hands of its forelimbs very strongly resemble the hands of the wings of the archeopteryx, and remotely the hands of modern birds. Being "broken", the hands presumably folded on the sides of the animal and most likely possessed feathers (as in the bird-like ancestors of Deinonychus). There are hooks on the ribs, like those of birds. The light bones of the animal and the stiff, tendon-covered tail (improving maneuverability when turning) indicated its high speed, and for the first time led paleontologists to the idea that dinosaurs were warm-blooded. Like all dromaeosaurs, Deinonychus had a “fork” in the front of the chest, which serves as a “shock absorber” for modern birds during strong wing beats.

Archeopteryx, who lived 150 million years ago, first showed a direct relationship between birds and reptiles, and is himself considered one of the first birds, as a whole strongly resembles a deinonychus reduced to the size of a dove. It differs from the latter in a large relative size of the brain, a decrease in the size of the jaws, and a reduction in the diapsid foramen. Archeopteryx was not an ancestor of birds, but is considered its closest relative, had a developed plumage, but could not fly, planning from tree to tree

Microraptor, a dromaeosaur dinosaur about the size of Archeopteryx, also closely resembled its older relative, making their skeletons almost indistinguishable to non-specialists. The animal lived 125 million years ago and in its way of life resembled Archeopteryx, having a developed black feather cover. He hunted insects and early birds, which he swallowed almost whole. Like the aforementioned Deinonychus dromaeosaurus, the pubic and ischial bones of the animal tend to "bend" back

A contemporary of the microraptor, and its "neighbor" in the region (northeastern China, southern Mongolia), Confuciornis was already halfway between dinosaurs and birds. Its jaws were devoid of teeth, the shoulder joint was highly developed, and instead of a long tail, the bird already had a pygostyle - a place for attaching the tail, which improved maneuverability during flight. Like the microraptor, the bird's ribs had hooks that rigidly fixed the abdominal cavity during flight. The site of articulation of the cervical vertebrae and the skull was halfway between its position in dinosaurs and modern birds. However, the structure of the shoulder joint did not allow the bird to fully master the flight, just like the underdeveloped keel. The hip joint still strongly resembled that of dromaeosaurs

Sinornis were among the first birds to master full-fledged flight. Despite this, the mechanics of their flight was very different from that of modern birds, as well as other enanciornis birds (“counterbirds”). There was a keel, a pygostyle, and the fingers of the forelimbs were partially fused to each other. The jaw apparatus and hip joint were more similar to those of dinosaurs than modern (fan-tailed) birds. An almost complete skeleton of Sinornis was discovered in the belly of a fossil Microraptor that hunted them.

Microraptor attacking a group of Sinornithes

However, the oldest birds that mastered a full-fledged flight were the ancestors of modern fan-tailed birds (Archaeornithura meemannae), the “cousins” of the enantiornithes in the clade of Ornithothoras - the euornites. The latter separated from the enantiornithes presumably at the very end jurassic 140-145 million years ago. Even then, the tendency of euornites to specialize in hunting in shallow water and on coastlines began to appear. Late Cretaceous ichthyornithids lived a lifestyle similar to gulls and terns and were physiologically almost the same as modern birds (see image below), except for the presence of teeth on both jaws. Of the colossal variety of gliding and flying dinosaurs, only a small part of the euornites, the ancestors of modern birds (neornithes), survived the Cretaceous-Paleogene extinction.

"Terrible Birds"
After the Cretaceous-Paleogene extinction, birds, along with mammals, began to fill the ecological niches left by their dinosaur brethren. So, after 15 million years, the first giant land birds appeared - non-flying crane-like birds. In size (up to 2.5 m in height and weight up to 300 kg) and way of life, they differed little from their relatives of dromaeosaurs, being also mostly predatory animals. The tailless bird's adaptation to a land way of life was reflected in the shift of the center of gravity to the center of the animal's body. Simplified the "work" of nature and the lightweight skull of the bird, instead of a complex jaw armed with a light but strong beak. As a result, modern land birds are more streamlined versions of theropod dinosaurs, without the weight wasted on powerful tail and neck muscles. Giant cranes have dominated America for the past 50 million years, losing the fight for survival. predatory mammal(wolf and cat) about 400,000 years ago. Below is a diagram of the skeleton of the largest crane-like group of fororakos - Kelenken.

The moment of hunting of another representative of the Phororrakos group, after which it was named - Phororacos. The size of the predator is greatly exaggerated, in fact, the fororakos were only slightly taller than an adult (up to 2 m), but they weighed twice as much and really were formidable hunters. Although the fororakos lived simultaneously with the genus Homo, they lived exclusively in the American part of the world and did not encounter people.

More about "terrible birds" in my future review " lost World South America".

The relative size of the brains of birds (the Encifalization Coefficient) is also often larger than that of similarly sized dinosaurs.

The encephalization coefficient simply expresses the ratio of the brain of an animal to the size of its body. Indirectly, it expresses the level of organization of the central nervous system - the intelligence of the animal. CE does not always objectively represent the true level of intelligence even within one species, but in general, from an evolutionary point of view, it has a linear dependence on the level of organization of living beings. Thus, higher birds and mammals have the highest EC values ​​(approximately parity). Already among this group of animals, the most complex behavior observed in animals with the highest EC values ​​(primates and cetaceans in mammals and corvids with parrots in birds).

This method allows us to imagine the level of intelligence typical of Late Cretaceous dinosaurs.

Dinosaur central nervous system

The brain of a Tyrannosaurus rex is considered one of the most studied for dinosaurs due to the good preservation of the skulls of these animals. In general, the structure of its brain is similar to modern crocodiles and has an encephalization coefficient approximately similar to that of an adult alligator. A very high value for such large predators of its time, second only to some progressive dromaeosaurs - bambiraptor, troodon and ornithomimus, whose EC was comparable to the average of modern birds.

A cast of the skull of a tyrannosaurus rex and an alligator. Pay attention to the highly developed olfactory bulb of both animals, which is quite typical for predatory reptiles (1). 2 - optic nerve; 3 - large hemispheres of the brain; 4 - optical share; 5 - cerebellum; 6 - vestibular apparatus; 7 - medulla oblongata

Casts of the cranium of various sauropodomorphs (in degrees, the extensibility of the jaw apparatus of the animal is indicated). Below is a description of the brain structure of Nigerosaurus.

The brain of birds and mammals is based on the striatum, inherited from their reptile ancestors. While mammals took the path of increasing the volume and functionality of the cerebral cortex (covering the striatum), archosaurs and later birds took the opposite path of increasing the volume and functionality of the striatum. Thus supreme nervous activity modern birds is provided by the striatum (more precisely, in the hyperstriatum, an analogue of the neocortex in mammals). The cortex provides only minor functions (presumably the sense of smell). Analogues of the hyperstratum in dinosaurs (yet?) have not been found, which again suggests a less developed than in higher birds theropod intelligence.

Evolution of the brain and olfactory lobes of the brain from dinosaurs (bambiraptor) to modern birds (pigeon). The lobes of the cerebral hemispheres of birds are larger than those of dinosaurs, while the olfactory lobes are significantly smaller. According to the researchers, this may be due to high level intelligence of birds, compensating for the lack of a relatively strong sense of smell

Graph showing the encephalization coefficient for different groups vertebrates. The coefficient of birds is about the same distance from that of their dinosaur ancestors as the CE of modern mammals is from the coefficient of their dinosaur ancestors

The bones of ancient lizards can not only give us an idea of appearance dinosaurs (morphology), but also to "tell" the life story of an individual animal. This, of course, is not only in the study of bone tissue damage that the animal has experienced during its life as a result of injuries and infections (as described in the doc. Film "The Ballad of Big Al", but also in the structure of the bones themselves.

The bones of reptiles, like a tree trunk, reveal peculiar "annual rings" in the cut, marking seasonal changes in the animal's growth rate. Dinosaur humerus or thigh bones are usually best suited for such purposes. Such an analysis (called a histological analysis) allows you to evaluate the growth rate of the animal, the time to reach puberty, sex and age at the time of death.

An example of annual rings on a cut of the bones of a herbivore Hippacosaurus. Below are visible thick light rings of accelerated growth of the animal in the first years of life, delimited by dark seasonal bands (droughts or cooling). Histological analysis estimates the achievement of puberty by 2-3 years (with sizes of 40% of the maximum for this species). The animal reached its maximum size (9m in length and 4t in weight) by the age of 10-12. Such growth rates are more characteristic of modern birds (ostriches) than modern progressive reptiles (crocodiles)

According to the traces of medullary tissue in the femur of the animal, sex determination is also possible with a high probability. ancient lizard(it is necessary for females as a reserve of calcium necessary for the egg shell). Similar tissue is deposited in the bones of archosaurs (in birds, like in theropod dinosaurs, it is stored in the femur) when they reach reproductive age. Dinosaur sexual maturity usually correlates with a sharp slowdown in the animal's growth. So, medullary tissue was found in the thigh of a female tyrannosaurus rex from Montana (USA) at the age (at death) of 18 years. The study of other specimens of tyrannosaurs (Rex species) also fixes a sharp slowdown in growth by 16-20 years. The oldest specimen discovered was about 28 years old at the time of death. The fact that most of the found remains of tyrannosaurus rex belong to individuals who lived only a few years after the onset of puberty indicates the very difficult conditions for the sexual selection of these creatures.

The "medullary principle" allows you to make very interesting discoveries. One of the discovered oviraptors (a sister group of cellurosaurs in relation to tyrannoraptors) at the time of death hatched clutch like modern birds. Histological studies did not find medullary tissue in the bones of the animal (photo below on the right), from which it was concluded that in this species the male, or at least both parents, incubated the clutch

In many species of modern birds, fathers are also involved in the "education" of their offspring. Below is a picture of a male cassowary with his chicks, which he also hatched. The animal resembles an oviraptor even externally. The picture on the left clearly shows the long claw on the first toe of the cassowary, similarly to " terrible claws» deinonychosaurs. However, unlike the latter, it is used to protect the animal from predators.

"Exam" of nature

Sometimes nature gives us a gift that allows us to correct our ideas about dinosaurs.

In 2000, in North America a well-preserved "mummy" of a herbivorous dinosaur of the genus hadrosaurs was found called Dakota. When analyzing the remains, scientists found that these dinosaurs were 1 m longer in life, and their muscle mass was 25% more than previously thought.

Regarding the modeling of the muscular structure of dinosaurs, the video can be seen on the example of the process of virtual "recovery" of the muscles of the neck and skull of an allosaurus

Death met almost simultaneously the predatory velociraptor and its victim, the protoceratops, at the moment of the struggle, which captured the duel for 70 million years. One of the legs of the predator with its claw was in the neck of the protoceratops, which gave additional weight to the supporters of the theory that deinonychosaurs used large claws on the first toes mainly to damage the trachea or artery of the victim in the cervical region, and not the belly or chest (as cassowaries do). ), for which the claws were not strong enough

"Genes of the Ancients"

Yes, you read that right, the bones of dinosaurs can also give us an idea of ​​their genome, or rather the size of their DNA. Scientists studying cells bone tissue animals (osteocytes), noticed linear connection between osteocyte sizes and animal DNA. This allowed them to estimate the size of the genomes of prehistoric pangolins compared to modern birds and reptiles. Thus, crocodile DNA contains just over 3 billion nucleobase pairs (NB), while bird DNA contains on average 1.45 billion BN pairs (from 0.97 to 2.5 billion). According to scientists, the size of dinosaur DNA varies greatly between lizards and ornithischians, respectively. The average genome size of ornithischian dinosaurs was close to that of modern reptiles - 2.5 billion HO pairs. The sauropods (theropods and sauropods) showed values ​​closer to modern birds, 1.8 billion pairs of HO.

DNA sizes in different types of living organisms.
In vertebrates, genome size correlates poorly with the number of genes. Neither the size of the DNA nor the number of genes have a positive correlation with the level of development of a living being. Thus, human DNA contains about 3 billion HO pairs. encoding 25 - 30,000 genes, far from a record in the animal kingdom. The vast majority of DNA is almost not involved in the life of a vertebrate cell (the so-called "genetic garbage"), and can be significantly "truncated" without serious consequences for animals.

It turns out that the ornithischian and lizard dinosaurs presumably took different paths from a common Triassic ancestor that had a typically large genome for reptiles. The lizards, for the most part, mastered bipedal locomotion (theropods), which required a radical reduction in the genome to optimize the circulatory system (reduction of the erythrocyte genome to reduce their size). Accordingly, already later, in the Jurassic and Cretaceous period, such a genome was preserved in maniraptor theropods, which gradually switched to active flight - real birds.

Relative sizes of erythrocytes in different groups of living beings.

Only mammals do not have nuclei in red bodies, which did not require a radical reduction in DNA during the development of metabolism. The erythrocytes of birds are close in size to the erythrocytes of mammals, but, like reptiles, they have nuclei.

These data are additional indirect evidence in favor of the hypothesis of the appearance of modern birds from theropod dinosaurs of the Jurassic period. However, feathers are also not exclusively a bird monopoly, and along with the bones of ancient lizards, fossil evidence of a developed feather “wardrobe” that “true” dinosaurs had was left to us.
In the next part of the review, we will talk about the evolution of the feathered "wardrobe" of dinosaurs, their path from simple decorations during mating games to the assimilation of a full-fledged flight by maniraptors. Add tags

"And why don't people fly like... dinosaurs?" ©

For the first time, the thought of the giant-toothed origin of sparrows, ducks, geese and other feathered living creatures visited me on Sunday morning - some kind of stomping creature was galloping along the galvanized tide outside the window, commenting on its jumps with screams in high notes. Slightly pushing back the curtain, I found a bird of the starling system - and it was at this moment that the starling for some reason reminded me of the tyrannosaurus rex, popular with filmmakers. Yes, damn it - the same head turns, swaying of the body when walking, unpleasant cries! Is it really true that dinosaurs were among the ancestors of chilled chicken carcasses sold in retail chains?

Tyrannosaurus - close relative hummingbird

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 are 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, as in mammals. All birds are warm-blooded.

According to the school biology course, Archeopteryx is considered the great 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 research in recent decades, Archeopteryx was not a bird, to a greater extent it is a subspecies of dinosaurs, moreover, a dead end, i.e. not received further development and completely extinct millions of years ago. So who is he - the ancestor of birds?

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

Dromaeosaurids lived 66 million years ago, at the very end of the Cretaceous period. Strong, agile, about 180 cm tall and weighing about 15 kg, the dromaeosaurus was a successful hunter of live prey - long legs allowed it to accelerate up to 80 km / h, jump up to 7 m. Each leg had a long and sharp claw, with with which the dromaeosaurus pierced the skin of the victim in a jump, and also climbed trees for hunting 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 lizard, then in its size the dromaeosaurus was like modern ostriches.

In the oviraptosaur family, paleontologists have found the most major representative bird-dinosaurs in the history of the Earth, which had wings - a gigantoraptor, whose height exceeded 3 meters, and the total body length with 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 a toothy mouth characteristic of dinosaurs, it had ... a bird's beak! Like dromaeosaurs, Gigantoraptor used short wings to slow down while chasing prey.

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

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

In conclusion, I present to you Avimimus, a small member of the oviraptosaur family - no more than 70 centimeters tall, weighing about 15 kg. This dinosaur could not fly because of all the same short wings, but it ran perfectly, its beak was equipped with teeth, which allows scientists to consider Avimima 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 also to the first birds - protoavis, ichthyornis, enantiornis, etc., which feathered dinosaurs ate 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 blood circulation (arterial and venous) separated from each other allowed them to maintain body temperature regardless of temperature. 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 insulate their body with feathers, but either they evolved too slowly, or their modernization stopped there - nevertheless, it was the era of dinosaurs that gave rise to modern birds.

The mystery of the origin of birds has been of concern to paleontologists for a very long time. And the more various fossils of extinct ancient birds and feathered dinosaurs can be found, the more confusing the history of the emergence of birds familiar to us becomes.

One after another, various signs, seemingly purely avian, are found in bipedal dinosaurs - theropods. These are feathers, and beaks, and various features of the skeleton, and even incubation of eggs. It is not surprising that with the great similarity between birds and small bipedal dinosaurs, it was them, theropods, who began to be considered avian ancestors. This hypothesis has now become dominant in scientific world, in many popular science publications and films you can even come across a phrase like "if you want to see a living dinosaur - look at the dove outside your window - there it is!". Of course, this is an exaggeration, even if birds evolved from dinosaurs, they are definitely not dinosaurs anymore. But did birds really come from them?

Paleontologists Devon Quick and John Ruben of Oregon State University answer this question in the negative. They compared the respiratory systems of modern birds and extinct theropod dinosaurs and concluded that these systems are completely different. The results of their research are published in the Journal of Morphology.

Birds, which need a lot of energy to fly, have a very different respiratory system from that of mammals. It is much more powerful and efficient - after all, in birds, the lungs do not work on the principle of "inhaled-received oxygen - exhaled exhaust air", like ours. Their air flows through the lungs in an almost constant flow. This is achieved thanks to special outgrowths - air sacs, anterior The posterior, abdominal sac, serves as a reservoir into which air is pumped during inhalation - when exhaled, this air goes through the lungs and there it releases the oxygen contained in it.

It seems that the currently unique air-sac respiratory system was much more widespread in the animal kingdom in the past, in the Mesozoic. "Ammonit.ru" wrote that traces of air sacs were found on the skeletons of pterosaurs and even large carnosaurs. The fact is that air sacs partially penetrate into the cavities of large bones and their traces can be recognized on the skeleton.

But paleontologists do not yet know exactly how these bags were located in the body cavities of extinct animals. On the other hand, it is well known that in modern birds, the posterior air sac, which occupies a rather large volume in the bird's body, is supported by the femur.

It was this anatomical feature that the researchers drew attention to. In general, a short femur, inactive and in a position close to horizontal, is a feature of all modern birds, including flightless ones. The femurs limit the expansion of the sac during inhalation.

But if in birds the thigh is practically not involved in walking, then how do they move on the ground? If you look at any bird, for example, at an ordinary crow or a sparrow, you will notice that in their paws their knees seem to be turned back, and not forward, like ours. In fact, what we see is not the knees, but the ankle joint, it's just that birds have an additional bone - the tarsus, which is not found in the legs of mammals. It is formed by the fusion of the bones that we have in the foot. It is this anatomical feature allows birds to create an additional joint and "free" the hip.

One of the authors of the study, John Reuben, says that in all land vertebrates, including dinosaurs, the hip was involved in locomotion, therefore, even in the presence of air sacs, their respiratory system was arranged differently than in birds. So dinosaurs could not be the ancestors of birds. In addition, Ruben recalls, real birds existed in the early Cretaceous, and possibly in the Jurassic, when bird-like bipedal dinosaurs only appeared.

But if birds didn't evolve from dinosaurs, then who did they? Probably, the authors of the study say, from some early archosaurs (which used to be called thecodonts) back in the Triassic. In this case, the similarity of birds with dinosaurs is also understandable - after all, both dinosaurs and pterosaurs also descended from archosaurs, and they could inherit feathers and some other anatomical features from a common ancestor.

Will this study put an end to the debate about the origin of birds? Of course not. Long before him, many paleontologists, including the well-known Russian expert on the origin of birds E.N. Kurochkin from the Paleontological Institute of the Russian Academy of Sciences did not share the "dinosaur" theory. But the complexity of this issue is not only in the fact that only bones, eggs and body prints have come down to us from ancient birds and dinosaurs, and all this is not always in good condition, but also in the fact that in the Jurassic and Cretaceous periods a variety of flying and birds there were much more creatures than now. There were real fan-tailed birds, there were extinct enanciornis birds - also birds, but obviously descended from other ancestors, there were Confuciusornis - another branch of birds, there were gliding dinosaurs - microraptors, and just running feathered dinosaurs. And it is very difficult to understand all this, who descended from whom, who descended from common ancestors, and who had completely similar signs as a result of convergence - development in similar conditions - it is very difficult to figure it out. But paleontology does not stand still, so we are sure to expect new interesting discoveries in this area.

Modern birds are very different from their related vertebrates. Until recently, their origin was one of the great mysteries of biology. Feathers, toothless beaks, hollow and deep breastbones are just some of the special features that other animals do not have. Watching birds does not explain how they got feathers and the ability to fly. Over the past decades, new discoveries and new research methods have appeared that have allowed paleontologists to make several discoveries. Fossils found in the area of ​​China, South America, as well as samples stored in museums, which can now be studied using new technologies, have caused another wave of interest in the study of the history of bird evolution. Thanks to this, a theory of their origin from small ones that lived on Earth at the end of the Jurassic period appeared earlier.

The beginning of the study of the origin of birds

Scientists have been thinking about the evolution of birds ever since Charles Darwin laid out his theory of evolution in On the Origin of Species. In 1861, a year after the publication of Darwin's treatise, an ancient bird's feather was found in Bavarian limestone deposits that were about 150 million years old. The following year, a skeleton of an animal was found that had bird-like wings and feathers, a very long bony tail, and a jaw with teeth. It was found in the same region. The fossilized skeleton was named Archeopteryx. He became the first ancient animal found with plumage. The skeletal anatomy of Archeopteryx provided clear evidence that dinosaurs were the ancestors of birds, but in 1861 scientists had not yet been able to establish this connection. Then the study of the evolution of birds and the hunt for the ancestors of modern bird species began.

Anatomical structure of Archeopteryx

The fossil was discovered in the early 1860s. For a long time the famous find from the late Jurassic was unique. She was the only one who could give any information about how the evolutionary transition from reptiles to birds could have occurred, since it combined features of both birds and reptiles. The structure of Archeopteryx had much in common with the structure of birds. For example, feathers along the front paws, which became wings. But, unlike modern species, teeth and a bony tail were also present.

The first theories about animals of the Jurassic period

It is worth noting that many of the bones of the animal, including the front paws, shoulder girdle, pelvis and legs, were distinct, not fused, as in its descendants. A few years later, Thomas Henry Huxley became the first scientist to find a connection between the structure of birds and dinosaurs. He compared the hind limbs of a giant dinosaur with an ostrich and noted 35 signs that prove that they are related to each other. Huxley presented his results to the Geological Society. But in 1870 in London, paleontologist Harry Govier Seeley decided to challenge the hypothesis of the origin of birds and their relationship to dinosaurs. Seeley suggested that the hind limbs of an ostrich and a dinosaur might look similar only because these animals were large and bipedal, and their hind limbs were used in similar conditions. Also, dinosaurs were even bigger than ostriches and none of them could fly. The scientist had a question, how then can birds fly if they evolved from a dinosaur.

Gerhard Heilmann's theory

The mystery again interested scientists after about half a century. In 1916, Gerhard Heilmann, a medical doctor with an interest in paleontology, published a brilliant book in Danish on the history of the origin of birds, which was translated into English in 1926 under the title The Origin of Birds. Heilman showed that birds were anatomically more similar to theropod dinosaurs than to any other fossil group. But there was one inevitable discrepancy: the theropods clearly lacked clavicles, the same ones that merge into a fork in birds.

Disadvantages of Gerhard Heilmann's theory

Because of the fact that other reptiles had clavicles, Heilman suggested that the theropods, in particular the Triassic Pseudosuchia, lost them for some reason. For him, this loss meant that birds could not evolve from this dinosaur species. So he was convinced, erroneously later found out, that the function of the clavicles, lost during evolution, could not be restored. Birds, he argued, must have evolved from a more archaic reptilian group that had clavicles.

Like Seeley earlier, Heilman concluded that the similarities between birds and dinosaurs must simply reflect the fact that both groups were bipedal. His findings influenced paleontological research and were a priority for a long time, although new information that has appeared has refuted some facts. But until now, some scientists adhere to it. Two separate studies have shown that theropods did indeed have clavicles. In 1924, an anatomical drawing of an unusual theropod with parrot plumage was published. It was called an oviraptor, and its existence disproved Heilmann's theory.

New evidence

In 1936, Charles Kamp of the University of California at Berkeley found the remains of a small early Jurassic theropod and wanted to put an end to the clavicle story. But the proof of the fallacy of Heilmann's theory was recognized by few. Recent studies have found clavicles in many theropods. Based on the structure of birds at the present time, as well as as a result of a number of studies, Archeopteryx has been called an intermediate link in the history of the evolution of birds. But the question remained: between which reptiles? Further fossil birds have been found in layers below the Early Cretaceous. Most of them have been discovered since the early 1990s, mainly in China. Meanwhile, more than thirty species of birds from the Cretaceous period are known. In addition, a large number of small bipedal bipedal dinosaurs have been discovered, with features characteristic of ancient birds. Thus, the gap between dinosaurs and birds, thanks to the study of fossils, has become much smaller.

Ostrom's theory

Finally, centuries after Huxley's controversial presentation to the Geological Society of London, John H. Ostrom of Yale University revived the idea that birds were related to theropods. He directly suggested that the birds are their direct descendants. In the late 1960s, Ostrom described the skeletal anatomy of the predatory theropod Deinonychus, which was the size of a human teenager and lived on Earth about 115 million years ago, during the Early Cretaceous. In his later published work, Ostrom went on to define the anatomy of birds and the group of features they, including Archeopteryx, shared with Deinonychus and other theropods, but not with other reptiles.

Based on this data, he concluded that birds descended directly from small theropod dinosaurs. After the theory was put forward, Ostrom continued to collect his evidence for the origin of birds from theropods. He used a new method of deciphering the relationships between organisms, applying it in museums natural history in New York, Paris and elsewhere. This method is called cladistics or phylogenetic systematics. Since it became the standard for comparative biology, its use strongly justified Ostrom's conclusions.

Research in the 1970s

In the 1970s, scientists continued to be interested in some of the common unique features of Archeopteryx that make it related to some animals of the Jurassic period. Among them were those very small carnivorous dinosaurs moving on two legs, which were called theropods. After carefully studying these traits, scientists again put forward the theory that they may have been the ancestors of birds. Leading paleontologists built evolutionary trees, and after that they were even more convinced that they were right.

What is a cladogram

These trees, otherwise known as the cladogram, are the current gold standard in the analysis of evolutionary relationships between animals. The method itself is called cladistics. Practitioners of cladistics determine the evolutionary history of a group of animals by studying different kinds of traits. In the process of evolution, an animal may develop a new, genetically determined trait that will be passed on to its descendants. Therefore, paleontologists can conclude that two groups that share a unique set of such new or acquired traits are more closely related to each other than to animals that lack those traits. Nodes or branch points on a cladogram indicate the appearance of a lineage with a new set of derived traits. As a result, the birds seemed to scientists to be just a branch on the dinosaurs' tree of life. In the works of J. Ostrom in the mid-1970s, theropods received the status of the most probable group for the ancestors of birds. Therefore, today the idea that birds are feathered dinosaurs is practically uncontested among evolutionary theorists.

Features of the cladistics method

Traditional methods of grouping organisms on the basis of similarity and difference may exclude a species from a group just because it has traits that were not found in other members. In contrast, cladistic groups have been based solely on certain groups of commonalities that are particularly informative. This method begins with the Darwinian precept that evolution continues when a new hereditary trait appears in some organisms and is passed on genetically to its descendants. The prescription indicates that two groups of animals that share such new traits are more closely related to each other than those that share only the original, but not the inherited derivatives. By identifying common derived traits, cladistic practitioners can determine relationships among the organisms under study. The results of such analyzes, which are usually investigated, can be presented in the form of a cladogram. The tree diagram depicting the order in which new characteristics and new creatures appeared reflects the order in which evolution occurred.

Cause of feathers in birds

As birds evolved and moved away from dinosaurs called theropods, many of their features changed and improved. If you take a closer look, it becomes quite obvious that a set of these characteristic features developed for a long time and served to perform a specific function. For example, the appearance of plumage in a small theropod was associated with the need to isolate certain areas of the skin and at first looked more like hair. The first bird feathers may have had different color patterns. There is a version that they were designed for camouflage, recognition of their appearance and other functions.

Comparison of the anatomical structures of birds and dinosaurs

Comparative anatomy of birds and theropods helped link them to each other. She also identified some ways in which these characteristics were changing as dinosaurs became closer to birds and birds became more modern. For example, in the pelvis, the pubic bone, initially directed forward, later shifts vertically or backward. In the forelegs, the relative proportions of the bones remained fairly constant in early birds, but the carpus has changed. In some species, the bone in the wrist has taken the form of a crescent. As a result, her shape contributed to the possibility of takeoff. The broad, boomerang-shaped fork of the first feathered dinosaurs became thinner and formed a deeper arc when this feature became necessary for flight.

Common Features of Dinosaurs and Birds

Gauthier's research in recent times, demonstrate that many features traditionally thought to be unique to birds actually predate them, in their theropod ancestors. Many of these properties helped their original owners survive. These same traits and several others were eventually used or modified for flight and tree life. The avian characteristics of theropods that evolved to birds did not appear immediately, and some were present before theropods themselves emerged. They were still among the dinosaurs that existed before. For example, the immediate ancestor of theropods was bipedal and moved like a bird. He was small and carnivorous. It had front legs, like early birds. In addition, the second, and not the third finger, as in other reptiles, was longer. In the ancestors of dinosaurs, the ankle joint became articulated, and the bones of the foot became elongated. Many of the changes in leg structure are thought to have contributed to the increase in stride length and running speed. This property will one day help avian theropods take flight.

The world's largest flying bird and the smallest

Giant birds lived on Earth over 6 million years ago. The largest flying bird in the world was the Argentavis. He lived in Argentina and belonged to the falcon family. An adult bird reached 2 meters in height, and its skull was about half a meter long. Huge wings in scope were like a three-story house. The smallest bird still exists today. It's wide known species- bee hummingbird. The length of its body usually does not exceed 6 cm. The habitat of the hummingbird is the steppe regions of the Brazilian province of Minas Gerais. The smallest bird feeds on the nectar of flowers and very quickly flaps its wings like a bee, which is why it got its name.