1. What facts may indicate a connection between extinct and modern plants and animals?
Answer. According to the synthetic theory of evolution, the evolutionary process occurring in nature is divided into two stages: microevolution and macroevolution.
Macroevolution involves processes leading to the emergence of systematic units larger than a species. By studying macroevolution, modern natural science has accumulated a number of scientific facts proving the evolution of the organic world. Any scientific fact that proves at least one of the following points can be considered proof of evolution.
Unity of the origin of life (the presence of common characteristics in all living organisms).
Relationships between modern and extinct organisms or between organisms in a large systematic group (the presence of common characteristics in modern and extinct organisms or in all organisms in a systematic group).
The action of the driving forces of evolution (facts confirming the action of natural selection).
Evidence of evolution obtained and accumulated within the framework of a particular science constitutes one group of evidence and is called by the name of this science.
Paleontology is the science of the fossil remains of extinct organisms. The founder of evolutionary paleontology is considered to be the Russian scientist V. O. Kovalevsky. Evidence of evolution includes fossil transitional forms and phylogenetic series of modern species.
Fossil transitional forms are extinct organisms that combine the characteristics of more ancient and evolutionarily younger groups. They allow us to identify family ties that prove historical development life. Such forms are established both among animals and among plants. The transitional form from lobe-finned fish to ancient amphibians - stegocephalians - is Ichthyostega. The evolutionary connection between reptiles and birds can be established by the first bird (Archaeopteryx). The link between reptiles and mammals is the lizard from the therapsid group. Among plants, the transitional form from algae to higher spores are psilophytes (the first land plants). The origin of gymnosperms from pteridophytes is proved by seed ferns, and the origin of angiosperms from gymnosperms by cycads.
Phylogenetic (from the Greek phylon - genus, tribe, genesis - origin) series - sequences of fossil forms, reflecting the historical development of modern species (phylogeny). Currently, such series are known not only for vertebrates, but also for some groups of invertebrate animals. Russian paleontologist V. O. Kovalevsky restored the phylogenetic series of the modern horse
2. What types of ancient plants and animals do you know?
Answer. Exactly 75 years ago, off the coast of southern Africa, the oldest fish in the world was discovered - coelacanth, which existed on Earth hundreds of millions of years ago. In honor of this event, we invite you to learn about her and other ancient animals and plants that inhabit our planet today.
It was previously believed that these fish became extinct in the Late Cretaceous (100.5 - 66 million years ago), but in December 1938, curator of the East London Museum (South Africa) Marjorie Courtney-Latimer discovered a fish with hard scales and unusual fins in the catch of local fishermen . It later turned out that this fish lived hundreds of millions of years ago and is a living fossil.
Since this coelacanth was discovered in the Chalumna River, it was named Latimeria chalumnae. And in September 1997, in the waters near the city of Manado, located on the northern coast of the island of Sulawesi, scientists noticed a second species of these fish - Latimeria menadoensis. According to genetic studies, these species separated 30-40 million years ago, but the differences between them are small.
2. Ginkgo biloba.
In the wild, this plant grows only in eastern China. However, 200 million years ago it was distributed throughout the planet, especially in the Northern Hemisphere, in areas with a temperate climate and high humidity. In Siberia of the Jurassic and Early Cretaceous periods, there were so many plants of the Ginkgo class that their remains are found in most deposits of those periods. According to researchers, in the autumn of that time the earth was literally covered with ginkgo leaves, like a carpet.
3. The small deer, or kanchil, is not only the smallest (its height at the withers is no more than 25 centimeters, and its maximum weight is about 2.5 kilograms), but also the most ancient species of artiodactyls on Earth. These animals existed 50 million years ago, just when orders of ancient ungulates began to form. Since that time, the kanchila has remained almost unchanged and resembles its ancient ancestors more than other species.
4. Mississippi shellfish.
An alligator-like fish, the Mississippi shellfish is one of the oldest fish living on Earth today. In the Mesozoic era, its ancestors inhabited many bodies of water. Today, the Mississippi shellfish lives in the lower Mississippi River valley, as well as in some freshwater lakes in the United States.
These small freshwater crustaceans are considered the most ancient creatures living on Earth today. Representatives of this species have hardly changed since the Triassic period. At that time, dinosaurs had just appeared. Today, these animals live on almost every continent except Antarctica. However, the species Triops cancriformis is most common in Eurasia.
6. Metasequoia glyptostroboides.
These conifers were widespread throughout the Northern Hemisphere from the Cretaceous to the Neogene. However, today metasequoia can only be seen in the wild in central China, in the provinces of Hubei and Sichuan.
7. Goblin Shark.
The genus Mitsukurina, to which this species of shark belongs, first became known through fossils that date back to the Middle Eocene (about 49-37 million years ago). The only living species of this genus, the goblin shark, which lives in the Atlantic and Indian oceans, has retained some primitive features of its ancient relatives and is today a living fossil.
Questions after § 61
1. What is macroevolution? What do macro- and microevolution have in common?
Answer. Macroevolution is supraspecific evolution, in contrast to microevolution, which occurs within a species, within its populations. However, there are no fundamental differences between these processes, since macroevolutionary processes are based on microevolutionary ones. In macroevolution, the same factors operate - the struggle for existence, natural selection and associated extinction. Macroevolution, like microevolution, is divergent in nature.
Macroevolution occurs over historically vast periods of time, so it is inaccessible to direct study. Despite this, science has a lot of evidence indicating the reality of macroevolutionary processes.
2. What evidence of macroevolution does paleontological data give us? Give examples of transitional forms.
Answer. Paleontology studies the fossil remains of extinct organisms and determines their similarities and differences with modern organisms. Paleontological data allows us to learn about the flora and fauna of the past, reconstruct the appearance of extinct organisms, and discover connections between ancient and modern representatives of flora and fauna.
Convincing evidence of changes in the organic world over time is provided by a comparison of fossil remains from earth layers of different geological eras. It allows us to establish the sequence of origin and development of different groups of organisms. For example, in the most ancient strata, remains of representatives of types of invertebrate animals are found, and in later strata, remains of chordates are found. Even younger geological strata contain the remains of animals and plants belonging to species similar to modern ones.
Paleontological data provide a wealth of material about the successive connections between various systematic groups. In some cases, it was possible to establish transitional forms between ancient and modern groups of organisms, in others, it was possible to reconstruct phylogenetic series, that is, series of species that successively replace one another.
A group of wild-toothed reptiles was found on the banks of the Northern Dvina. They combined the characteristics of mammals and reptiles. Animal-toothed reptiles are similar to mammals in the structure of the skull, spine and limbs, as well as in the division of teeth into canines, incisors and molars.
The discovery of Archeopteryx is of great interest from an evolutionary point of view. This pigeon-sized animal had the characteristics of a bird, but also retained the features of reptiles. Signs of birds: hind limbs with a tarsus, the presence of feathers, general appearance. Signs of reptiles: a long row of caudal vertebrae, abdominal ribs and the presence of teeth. Archeopteryx could not be a good flyer, since its sternum (without a keel), pectoral muscles and wing muscles are poorly developed. The spine and ribs were not a rigid skeletal system that was stable during flight, as in modern birds. Archeopteryx can be considered a transitional form between reptiles and birds. Transitional forms simultaneously combine the characteristics of both ancient and more evolutionarily younger groups. Another example is ichthyostegas, a transitional form between freshwater lobe-finned fish and amphibians.
3. What is the significance of reconstructing phylogenetic series?
Answer. Phylogenetic series. For a number of groups of animals and plants, paleontologists were able to recreate a continuous series of forms from ancient to modern, reflecting their evolutionary changes. Russian zoologist V. O. Kovalevsky (1842–1883) recreated the phylogenetic series of horses. In horses, as they transitioned to fast and long running, the number of toes on their limbs decreased and at the same time the size of the animal increased. These changes were a consequence of changes in the lifestyle of the horse, which switched to feeding exclusively on vegetation, in search of which it was necessary to travel long distances. It is believed that all these evolutionary transformations took 60–70 million years.
The study of phylogenetic series constructed on the basis of data from paleontology, comparative anatomy and embryology is important for further development general theory evolution, building a natural system of organisms, recreating a picture of the evolution of a specific systematic group of organisms. Currently, to construct phylogenetic series, scientists are increasingly using data from such sciences as genetics, biochemistry, molecular biology, biogeography, ethology, etc.
Methods of phylogenetic research are organically connected with methods of studying the facts of evolution. Until now, the morphological method should be considered the main method of phylogenetic research, since transformations in the form of an organism remain the most obvious fact and allow us to trace the phenomena of species transformation with a great degree of success.
It does not follow from this, of course, that other methods are not applicable to phylogenetic studies - physiological, ecological, genetic, etc. The form and function of an organism are inextricably linked. Any organism is formed under the influence of specific environmental factors, it interacts with it, it is in certain connections with other organisms. However, the form of an organism, its structure always remains a sensitive indicator of all these connections and serves as a guiding thread for the researcher of phylogenetic issues. The morphological research method occupies a leading position in the study of phylogeny and its conclusions have generally been confirmed when tested by other methods. The great advantage of the morphological method is the availability of its combination with a comparative method of research, without which it is impossible to detect the very fact of transformation of living systems. The validity of the morphological method is greatly enhanced by the fact that it is essentially deeply self-critical, since it can be applied in various directions.
If we have large paleontological material (for example, the evolution of the horse), we can apply the comparative morphological method to successive series of ancestors and descendants and thus identify the directions and methods of evolution of a given group. The figure gives an idea of the essence of the comparative morphological method as applied to the ancestors of the horse. The sequential reduction of the lateral fingers and the development of the middle (III) finger show the direction evolutionary development"horse row".
Comparison of the limbs of jerboas with a decreasing number of fingers and increasing specialization. 1 - small jerboa Allactaga elator, 2 - Salpingotas Koslovi, 3 - bushy-footed Dipus sagitta. I-V - fingers from first to fifth (According to Vinogradov)
Further, paleontological data are in harmony with comparative anatomical studies of modern forms. The figure compares the limbs of three forms with a decreasing number of fingers. Although this is not a phylogenetic series, it does give the impression that all three limbs are the result of the manifestation of similar processes that have reached different stages of development. Therefore, the comparative morphological method, in relation to modern forms, regardless of paleontology, makes it probable that, for example, a single-toed foot should have developed from a multi-toed one. When these conclusions are added to the facts of comparative embryology, showing that, for example, in a horse embryo, lateral toes are formed, and then they are gradually reduced, then our conclusion about the origin of the one-toed horse from a many-toed ancestor becomes even more probable.
The coincidence of these data shows that the facts of paleontology, comparative anatomy of adult forms and comparative embryology mutually control and complement each other, forming in their totality a synthetic triple method of phylogenetic research proposed by Haeckel (1899) and which has not lost its significance today. It is accepted that the coincidence of data from paleontology, comparative anatomy and embryology, to a certain extent, serves as proof of the correctness of phylogenetic constructions.
These are the most general principles phylogenetic studies.
Let us now consider the briefly described elements of a unified method of phylogenetic research.
Paleontological data are most convincing. However, they have a major defect, namely, the paleontologist deals only with morphological characteristics and, moreover, incomplete ones. The organism as a whole is beyond the scope of paleontological research. In view of this, it is especially important for a paleontologist to take into account all the available signs of the animals whose remains he is dealing with. Otherwise, his phylogenetic conclusions may be erroneous.
Let us assume that forms A, B, C, D, E, E replace each other in successive geological horizons, and that the paleontologist has the opportunity to observe a certain sum of their characteristics - a, b, c, etc. Let us further assume that the form A has the characteristics a 1, b 1, c 1, and in forms B, C, D, ... these characteristics are changed (respectively a 2, b 2, c 2 .. a 3, b 3, c 3 ..., etc. .). Then over time we get the following series of data
This tablet corresponds, for example, to a “row” of equine ancestors, where from Eopippus to horse we have a succession in the development of a number of characteristics. The table shows the successive development of all leading characteristics. Each subsequent sign (for example, a 4) is derived from each previous one (for example, a 3). In such cases it becomes probable that the series A, B, C, D, E, E forms phylogenetic series, i.e. a number of ancestors and their descendants. This is the series from eohippus to horse and some others.
Now suppose we are dealing with the following data,
that is, we state a number of forms that successively replace each other in time, and according to one of the signs (b) we get a picture of sequential development from b 1 to b 5. Nevertheless, our series is not a phylogenetic series, since, for example, with respect to characters a and b we do not observe consistent specialization. For example, species A has formula A (a 1, b 1, b 1), but species B is clearly not its direct descendant, since it has formula B (a 4, b 2, b 2), etc. Obviously, Here we are dealing with successive “fragments” of a phylogenetic tree, many branches of which have not been found. Therefore, the series A, B, C, D, D, E is actually equal to A, B 1, C 2, D 3, D 1. This series is called stepped. To explain the differences between it and the phylogenetic series, we will use a picture showing the evolution of the horse. Here the following series will be phylogenetic: eohippus, orohippus, mesohippus, parahippus, merigippus, pliohippus, plesippus, horse. For example, the following series of forms would be stepped: hyracotherium, epihippus, myohippus, anchytherium, hipparion, hippidium, horse. All these are not ancestors and descendants, but successive but scattered side branches of the phylogenetic tree.
As you can see, the stepped series is of great working importance, since, based on it, one could conclude that the horse descended from a polydactyl ancestor.
Finally, you may encounter adaptive range, showing the development of any adaptation. Such a series may be part of a phylogenetic series, for example, the adaptation of a horse’s leg to running, but often this is not the case, and an adaptive series can be made up even at the expense of modern forms that do not form a phylogenetic series at all. As we see, a paleontologist has to face great difficulties. His material is fragmentary and incomplete.
Some compensation for the incompleteness of paleontological data, however, is the possibility of extending environmental data to paleontology. A certain form of an organ (the structure of a leg, the structure of the dental apparatus, etc.) allows one to draw conclusions about the lifestyle and even the composition of food of extinct animals. This gives rise to the possibility of reconstructing their ecological relations. The corresponding field of knowledge, established in the works of V. O. Kovalevsky, was called paleobiology (Abel, 1912). It makes up for the fragmentation of the paleontologist’s ideas about extinct animals. With regard to forms devoid of a skeleton, paleontology provides only negligible material on phylogenetics, and in these cases comparative morphology with its method of comparative study of homologous structures of adult and embryonic forms of geological modernity comes first. The lack of paleontological data makes drawing phylogenetic inferences much more difficult. Therefore, our phylogenetic constructions are most reliable in relation to those forms for which paleontological material is known.
Nevertheless, even in the absence of paleontological data, the researcher does not remain unarmed. In this case, he uses another method, namely, the study of the stages of ontogenetic development.
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Question 1. What is the difference between macro- and microevolution?
By microevolution we mean the formation of new species.
The concept of macroevolution denotes the origin of supraspecific taxa (genus, order, clan, type).
Nevertheless, there are no fundamental differences between the processes of formation of new species and the processes of formation of higher taxonomic groups. The term “microevolution” in the modern sense was introduced by N.V. Timofeev-Resovsky in 1938.
Question 2. What processes are the driving forces of macroevolution? Give examples of macroevolutionary changes.
In macroevolution, the same processes operate as during speciation: the formation of phenotypic changes, the struggle for existence, natural selection, the extinction of the least adapted forms.
The result of macroevolutionary processes is significant changes in the external structure and physiology of organisms - such as, for example, the formation of a closed circulatory system in animals or the appearance of stomata and epithelial cells in plants. Fundamental evolutionary acquisitions of this kind include the formation of inflorescences or the transformation of the forelimbs of reptiles into wings and a number of others.
Question 3. What facts underlie the study and evidence of macroevolution?
The most convincing evidence of macroevolutionary processes comes from paleontological data. Paleontology studies the fossil remains of extinct organisms and establishes their similarities and differences with modern organisms. From the remains, paleontologists reconstruct the appearance of extinct organisms and learn about the flora and fauna of the past. Unfortunately, the study of fossil forms gives us an incomplete picture of the evolution of flora and fauna. Most remains consist of solid parts of organisms: bones, shells, and external supporting tissues of plants. Of great interest are fossils that preserve traces of burrows and passages of ancient animals, imprints of limbs or entire organisms left on once soft sediments.
Question 4. What is the significance of the study of phylogenetic series?Material from the site
The study of phylogenetic series constructed on the basis of data from paleontology, comparative anatomy and embryology is important for the further development of the general theory of evolution, the construction of a natural system of organisms, and the reconstruction of the picture of the evolution of a specific systematic group of organisms.
Currently, to construct phylogenetic series, scientists are increasingly using data from such sciences as genetics, biochemistry, molecular biology, biogeography, ethology, etc.
One of the best known and best studied is the phylogenetic series of modern single-toed ungulates. Multiple paleontological finds and identified transitional forms create a scientific evidence base for this series. The phylogenetic series of the horse, described by the Russian biologist Vladimir Onufrievich Kovalevsky back in 1873, remains an “icon” of evolutionary paleontology today.
Evolution through the centuries
In evolution, phylogenetic series are successively successive transitional forms that led to the formation of modern species. Based on the number of links, the series can be complete or partial, but the presence of successive transitional forms is a prerequisite for their description.
The phylogenetic series of the horse is considered evidence of evolution precisely due to the presence of such sequential forms that replace each other. The multiplicity of paleontological finds gives it a high degree of reliability.
Examples of phylogenetic series
The row of horses is not the only one among the examples described. Well studied and has high degree reliability of the phylogenetic series of whales and birds. And controversial in scientific circles and most used in various populist insinuations is the phylogenetic series of modern chimpanzees and humans. Disputes about the missing intermediate links here continue in the scientific community. But no matter how many points of view there are, the importance of phylogenetic series as evidence of the evolutionary adaptability of organisms to changing environmental conditions remains indisputable.
The connection between the evolution of horses and the environment
Multiple studies by paleontologists have confirmed the theory of O. V. Kovalevsky about the close relationship of changes in the skeleton of the ancestors of horses with changes in the environment. The changing climate led to a decrease in forest areas, and the ancestors of modern single-toed ungulates adapted to living conditions in the steppes. The need for rapid movement provoked modifications in the structure and number of fingers on the limbs, changes in the skeleton and teeth.
The first link in the chain
In the early Eocene, more than 65 million years ago, lived the first ancestor of the modern horse. This is a “low horse” or Eohippus, which was the size of a dog (up to 30 cm), rested on the entire foot of the limb, which had four (front) and three (back) fingers with small hooves. Eohippus fed on shoots and leaves and had tuberculate teeth. Brown coloring and sparse hair on a mobile tail - this is the distant ancestor of horses and zebras on Earth.
Intermediates
About 25 million years ago, the climate on the planet changed, and steppe expanses began to replace forests. In the Miocene (20 million years ago), mesohippus and parahippus appeared, more similar to modern horses. And the first herbivorous ancestor in the phylogenetic series of the horse is considered to be Merikhippus and Pliohippus, which entered the arena of life 2 million years ago. Hipparion - the last three-fingered link
This ancestor lived in the Miocene and Pliocene on the plains of North America, Asia and Africa. This three-toed horse, resembling a gazelle, did not yet have hooves, but could run fast, ate grass, and it was she who occupied vast territories.
One-toed horse - pliohyppus
These one-toed representatives appear 5 million years ago in the same territories as hipparions. Environmental conditions are changing - they are becoming even drier, and the steppes are expanding significantly. This is where single-fingeredness turned out to be a more important sign for survival. These horses were up to 1.2 meters high at the withers, had 19 pairs of ribs and strong leg muscles. Their teeth acquire long crowns and folds of enamel with a developed cement layer.
Horse we know
The modern horse, as the final stage of the phylogenetic series, appeared at the end of the Neogene, and at the end of the last ice age (about 10 thousand years ago), millions of wild horses were already grazing in Europe and Asia. Although the efforts of primitive hunters and the reduction of pastures made the wild horse a rarity already 4 thousand years ago. But two of its subspecies - the tarpan in Russia and the Przewalski's horse in Mongolia - managed to last much longer than all the others.
Wild horses
Today there are practically no real wild horses left. The Russian tarpan is considered an extinct species, and the Przewalski's horse is natural conditions does not occur. Herds of horses that graze freely are wild domesticated forms. Although such horses quickly return to wild life, they still differ from truly wild horses.
They have long manes and tails and are of different colors. Exclusively dun Przewalski's horses and mousey tarpans have trimmed bangs, manes and tails.
In Central and North America, wild horses were completely exterminated by the Indians and appeared there only after the arrival of Europeans in the 15th century. The feral descendants of the conquistadors' horses gave rise to numerous herds of mustangs, the numbers of which today are controlled by shooting.
In addition to mustangs, there are two species of wild island ponies in North America - on Assateague and Sable Islands. Semi-wild herds of Camargue horses are found in the south of France. Some wild ponies can also be found in the mountains and moors of Britain.
Our favorite horses
Man tamed the horse and bred more than 300 of its breeds. From heavyweights to miniature ponies and handsome racing horses. About 50 breeds of horses are bred in Russia. The most famous of them is the Oryol trotter. Exclusively white coat, excellent trot and agility - these qualities were so valued by Count Orlov, who is considered the founder of this breed.