The inconsistency of views on the immutability of animal species
The knowledge that the animal world did not remain constant for tens and hundreds of millions of years, but developed, did not come immediately. In ancient times and in the Middle Ages, it was assumed that nature is unchangeable, that all modern animals and plants have always been exactly the same. However, by the beginning of the 19th century. Facts became known indicating that in distant times the Earth was inhabited by other animals, not similar or little similar to modern ones. During excavations, their remains were found in the form of imprints and bones. Proponents of religion believed that extinct animals were trial, unsuccessful creations of God. Instead, he created modern animals, which have existed unchanged ever since. Even many scientists 180 years ago believed that all organisms on Earth appeared as we see them, and no changes occurred to them over the centuries. How and why evolution occurs was proven by the great English naturalist Charles Darwin in his book “The Origin of Species by Means of Natural Selection,” published in 1859.
The main driving forces of evolution
Darwin identified the main driving forces in the evolution of plant and animal organisms. These are variability, heredity and selection.
Variability
While studying the diversity of plant and animal species, Darwin first of all drew attention to the fact that even in the offspring of one pair of parents there are no two identical individuals in all respects. He found that among cultivated plants and domestic animals there is much more diversity, more varieties and breeds than the wild ancestors from which they originated. For example, there are several hundred breeds of dogs, and they are all descendants of the same species - the wolf. Several hundred breeds of pigeons have been created. However, among wild pigeons, only one species has characteristics similar to them (it also coos and nests in the same way) - the wild rock pigeon. Thus, during the time that has passed since the beginning of the domestication of the rock pigeon, the breeds of pigeons have changed a lot. Domestic pigeons differ in body size, beak color, plumage, etc. Darwin called differences between animals of the same species, the same breed variability. This is a property not only of animals, but also of plants and other living organisms.
Figure: Variability of animals using the example of different breeds of pigeons
Darwin believed that the reason for the variability of organisms lies in the influence of new living conditions that did not exist when their ancestors lived. There is little variability in wild pigeons living in the rocky areas of Western Europe, since natural conditions change very slowly. In rock pigeons that live near humans and belong to the same species, variability is significant, since humans constantly change environmental conditions.
Heredity
Darwin drew attention to the fact that all congenital characteristics are passed on from generation to generation. He called the ability of organisms to transmit innate characteristics to their offspring heredity. Puppies or kittens, for example, are very similar to each other and their parents. If new characteristics are not congenital, but arose during the life of the organism, then they cannot be inherited. It is known that dogs of some breeds, such as fox terriers, have their tails cut off from generation to generation. However, this new external characteristic (short tail) is not inherited. All Fox Terrier puppies are born with tails of normal length.
Breeding domestic animal breeds. Artificial selection
Man has bred many breeds of domestic animals: large and small cattle, horses, dogs, rabbits, chickens, ducks, pigeons. Breeds of fish - pond and aquarium - have also been developed.
Each time, having discovered some especially useful properties for himself in one of his domestic animals, a person singled out this animal from the rest, or, as Darwin said, selected it and preserved its offspring if it had the same useful characteristics. Thus, by selecting the longest-legged and fastest-running domestic dogs, we obtained the breed of greyhounds, and by selecting the shortest-legged ones, we obtained the dachshund. When they want to breed a dairy cattle breed, animals are selected for high milk yield and do not pay attention to body weight. When breeding meat breeds, the largest animals are selected, even if they give little milk - Darwin called this selection artificial, since it is carried out by a person.
Using artificial selection, people develop new breeds of domestic animals in a historically short time. So, the dog was domesticated about 15 thousand years ago. Several hundred dog breeds are now known.
Lesson type - combined
Methods: partially search, problem presentation, reproductive, explanatory and illustrative.
Target: mastering the ability to apply biological knowledge in practical activities, use information about modern achievements in the field of biology; work with biological devices, instruments, reference books; conduct observations of biological objects;
Tasks:
Educational: the formation of cognitive culture, mastered in the process of educational activities, and aesthetic culture as the ability to have an emotional and value-based attitude towards objects of living nature.
Educational: development of cognitive motives aimed at obtaining new knowledge about living nature; cognitive qualities of a person associated with mastering the fundamentals of scientific knowledge, mastering methods of studying nature, and developing intellectual skills;
Educational: orientation in the system of moral norms and values: recognition of the high value of life in all its manifestations, the health of one’s own and other people; environmental awareness; nurturing love for nature;
Personal: understanding of responsibility for the quality of acquired knowledge; understanding the value of adequately assessing one’s own achievements and capabilities;
Cognitive: ability to analyze and evaluate the impact of environmental factors, risk factors on health, the consequences of human activities in ecosystems, the impact of one’s own actions on living organisms and ecosystems; focus on continuous development and self-development; the ability to work with various sources of information, transform it from one form to another, compare and analyze information, draw conclusions, prepare messages and presentations.
Regulatory: the ability to organize independent completion of tasks, evaluate the correctness of work, and reflect on one’s activities.
Communicative: the formation of communicative competence in communication and cooperation with peers, understanding the characteristics of gender socialization in adolescence, socially useful, educational and research, creative and other types of activities.
Technologies: Health conservation, problem-based, developmental education, group activities
Types of activities (content elements, control)
Formation in students of activity abilities and abilities to structure and systematize the subject content being studied: collective work - study of text and illustrative material, compilation of a table “Systematic groups of multicellular organisms” with the advisory assistance of student experts, followed by self-test; pair or group performance of laboratory work with the advisory assistance of a teacher, followed by mutual testing; independent work on the studied material.
Planned results
Subject
understand the meaning of biological terms;
describe the structural features and basic life processes of animals of different systematic groups; compare the structural features of protozoa and multicellular animals;
recognize organs and organ systems of animals of different systematic groups; compare and explain reasons for similarities and differences;
establish the relationship between the structural features of organs and the functions they perform;
give examples of animals of different systematic groups;
distinguish the main systematic groups of protozoa and multicellular animals in drawings, tables and natural objects;
characterize the directions of evolution of the animal world; provide evidence of the evolution of the animal world;
Metasubject UUD
Cognitive:
work with different sources of information, analyze and evaluate information, transform it from one form to another;
draw up theses, various types of plans (simple, complex, etc.), structure educational material, give definitions of concepts;
carry out observations, perform elementary experiments and explain the results obtained;
compare and classify, independently choosing criteria for the specified logical operations;
build logical reasoning, including establishing cause-and-effect relationships;
create schematic models highlighting the essential characteristics of objects;
identify possible sources of necessary information, search for information, analyze and evaluate its reliability;
Regulatory:
organize and plan your educational activities - determine the purpose of the work, the sequence of actions, set tasks, predict the results of the work;
independently put forward options for solving assigned tasks, anticipate the final results of the work, choose the means to achieve the goal;
work according to plan, compare your actions with the goal and, if necessary, correct mistakes yourself;
master the basics of self-control and self-assessment for making decisions and making informed choices in educational, cognitive and educational and practical activities;
Communicative:
listen and engage in dialogue, participate in collective discussion of problems;
integrate and build productive interactions with peers and adults;
adequately use verbal means for discussion and argumentation of one’s position, compare different points of view, argue one’s point of view, defend one’s position.
Personal UUD
Formation and development of cognitive interest in the study of biology and the history of the development of knowledge about nature
Techniques: analysis, synthesis, inference, translation of information from one type to another, generalization.
Basic Concepts
Concepts: heredity, variability: indefinite and definite, struggle for existence, natural selection.
During the classes
Updating knowledge ( concentration when learning new material)
Have you found animal fossils in your area?
Why can't we say that paleontological findings disprove evolution?
3.What, in your opinion, are the reasons for the extinction of dinosaurs?
4.What does the presence of a fertilized egg indicate in all animals that reproduce sexually?
5.What are the main differences between paleontological and comparative anatomical evidence for the evolution of animals?
6. Why are the wings of a bird and the flippers of a whale considered homologous organs?
7.What is the difference between vestigial organs and atavisms; What do they have in common?
Learning new material(teacher's story with elements of conversation)
Charles Darwin on the reasons for the evolution of the animal world
Why are there many different types of animals?
Who is Charles Darwin?
What are Charles Darwin's services to science?
The reasons for the different levels of organization of animals, the differences between existing species and extinct ones, and the manifestations of atavisms have long been of interest to scientists and church ministers. The famous English scientist Charles Darwin (1809-1882) explained these phenomena most fully in his work “The Origin of Species”.
According to Darwin's teaching, the diversity of species was not created by God, but was formed due to constantly occurring hereditary changes and natural selection. In the process of survival of the fittest individuals, Darwin noted the presence of a struggle for existence, the result of which is the extinction of unadapted organisms and the reproduction of the most fit.
Heredity- the ability of organisms to transmit to their descendants their specific and individual characteristics or properties. Thus, a certain species of animal produces offspring that are similar to their parents. Some individual characteristics of animals can also be hereditary, for example, coat color and milk fat content in mammals.
Variability- the ability of organisms to exist in various forms, responding to environmental influences. Variability is manifested in the individual characteristics of each organism. In nature, there are no two absolutely identical animals. The born cubs differ from each of their parents in coloring, height, behavior and other characteristics. Differences in animals, as C. Darwin noted, depend on the following reasons: on the quantity and quality of food consumed, on fluctuations in temperature and humidity, on the heredity of the organism itself. Charles Darwin identified two main forms of variability that influence the evolution of the animal world - definite, non-hereditary, and indefinite, or hereditary.
Under certain variability Charles Darwin understood the occurrence of identical changes in related animals under the same environmental conditions. Thus, the thick fur of Transbaikal squirrels changed to sparse fur during their acclimatization in the forests of the Caucasus. Keeping rabbits in low temperatures results in thicker fur. Lack of food leads to stunted growth of animals. Consequently, a certain variability is a direct adaptation of animals to changed environmental conditions. Such variability is not passed on to descendants.
Under uncertain hereditary variability Charles Darwin understood the occurrence of various changes in a number of related animals under the influence of the same (similar) conditions. It is hereditary and individual, as it occurs randomly in one individual of the species and is inherited. An example is the appearance of sheep with short legs, the lack of pigment in the feathers of birds or in the fur of mammals.
Charles Darwin considered the struggle for existence to be one of the reasons for the evolution of the animal world. arising due to the intensive reproduction of organisms. A parent pair of any animal species produces numerous offspring. Out of the number of offspring born, only a few will survive to adulthood. Many will be eaten or die almost immediately after birth. Those who remain will begin to compete with each other for food, better habitats, and shelter from enemies. The descendants of those parents who are most adapted to the given living conditions will survive. Thus, the struggle for existence leads to natural selection - the survival of the fittest.
In nature, individuals of the same species differ from each other in many ways.. Some of them may be useful, and, as Darwin noted, “individuals having even a slight advantage over the rest will have the best opportunity of surviving and leaving the same offspring.” The process occurring in nature that preserves organisms most adapted to environmental conditions and destroys those that are not adapted is called natural selection. According to Charles Darwin, natural selection is the main, leading cause of the evolution of the animal world.
Do you know that:
Charles Darwin set off on a voyage on the Beagle in 1831, which determined his entire subsequent activity. The journey lasted 5 years. During this time, Charles Darwin collected a wealth of material, which served as the basis for such books as: “Diary of a Voyage”, “Zoological Results of the Voyage on the Beagle”.
The main work of Charles Darwin's life, “On the Origin of Species by Means of Natural Selection...” was published in 1859.
Why are there many different types of animals?
The existence of different species of animals is due to diverse environmental conditions. In the aquatic, soil, ground and air environments, there are a large number of life niches that are inhabited by different species. A struggle for existence and natural selection arises between them. Thus, the fittest individuals will survive.
Who is Charles Darwin?
Charles Darwin is a famous English scientist and biologist who created an evolutionary theory that remains reliable today. He outlined the essence of his teaching in his work “The Origin of Species.”
What are Charles Darwin's services to science?
Charles Darwin is the creator of evolutionary theory.
Answer the questions
1. What is the value of Charles Darwin’s book “The Origin of Species”?
Charles Darwin in this book for the first time most fully explained the reasons for the diversity of animal species, different levels of organization, the presence of rudiments and atavisms.
Why did Charles Darwin consider natural selection to be the main cause of evolution?
Charles Darwin assigned this role to natural selection because he believed that as a result of natural selection, the fittest individuals survive.
3. What does the concept of “struggle for existence” mean? Support your explanation with examples.
The struggle for existence is a competitive struggle between individuals of the same or different species for resources (food, territory). For example, many raptors and birds of prey live in families. Each pair occupies a certain territory in which it hunts. This means that a limited number of individuals can exist in a certain territory.
4. Is it possible to say that heredity and variability are inherent in all animals?
Heredity and variability under certain conditions are inherent in all organisms. Each new organism receives hereditary information in the form of a set of chromosomes from its parent individuals. Under the influence of the environment, organisms can change in response to new conditions. Organisms may not be subject to variability for quite a long time if their living conditions remain unchanged for a long time. This can explain the existence of relict species.
Charles Darwin's theory
Biography and views of Charles Darwin.
Basic principles of Charles Darwin's theory of evolution
Resources
Biology. Animals. 7th grade textbook for general education. institutions / V.V. Latyushin, V.A. Shapkin.
Active formsAndbiology teaching methods: Animals. Kp. for the teacher: From work experience, -M.:, Education. Molis S. S.. Molis S. A
Work program in biology 7th grade for teaching materials V.V. Latyushina, V.A. Shapkina (M.: Bustard).
V.V. Latyushin, E. A. Lamekhova. Biology. 7th grade. Workbook for the textbook by V.V. Latyushina, V.A. Shapkina “Biology. Animals. 7th grade". - M.: Bustard.
The history of animals has been studied most fully due to the fact that they have a skeleton and are therefore better established in fossilized remains. The earliest traces of animals are found at the end of the Precambrian (700 million years). It is assumed that the first animals originated either from the common trunk of all eukaryotes, or from one of the groups of ancient algae. Single-celled green algae are closest to the ancestors of the simplest animals (Protozoa). It is no coincidence that, for example, euglena and volvox, capable of both photosynthesis and heterotrophic nutrition, are classified by botanists as a type of green algae, and by zoologists as a type of protozoan animals. Over the entire history of the animal world, 35 types arose, of which 9 became extinct, and 26 still exist.
The diversity and quantity of paleontological documentation of animal history increases sharply in rocks dating back less than 570 Ma. years. For approximately 50 million. years, almost all types of secondary cavity animals with a strong skeleton appear quite quickly. Trilobites were widespread in the Silurian seas. The emergence of the chordate type (Chordata) dates back to less than 500 million years ago. years. Complexes of well-preserved fossils were found in the Berges Shale (Colombia), containing the remains of invertebrates, in particular soft-bodied organisms of the Annelida type, to which modern earthworms belong.
The beginning of the Paleozoic was marked by the formation of many types of animals, of which about a third exist today. The reasons for such active evolution remain unclear. In Late Cambrian times, the first fish appeared, represented by jawless fish - Agnata. Later, they almost all became extinct; lampreys survived from modern descendants. In the Devonian, jawed fish appeared as a result of such major evolutionary transformations as the transformation of the anterior pair of gill arches into jaws and the formation of paired fins. The first gnathostomes were represented by two groups: ray-finned and lobe-finned. Almost all living fish are descendants of ray-finned fish. Lobe-finned fish are now represented only by lungfishes and a small number of relict marine forms. Lobe-finned animals had bony supporting elements in their fins, from which the limbs of the first land dwellers developed. Previously, amphibians arose from the lobe-finned group, therefore, all four-legged vertebrates have their distant ancestor from this extinct group of fish.
The most ancient representatives of amphibians, Ichthyostegas, were found in Upper Devonian deposits (Greenland). These animals had five-fingered limbs with which they could crawl on land. Nevertheless, a number of features (a real caudal fin, a body covered with small scales) indicate that ichthyostegas lived mainly in water bodies. Competition with lobe-finned fish forced these first amphibians to occupy habitats intermediate between water and land.
The heyday of ancient amphibians dates back to the Carboniferous, where they were represented by a wide variety of forms, united under the name “stegocephals.” Among them, the most prominent are labyrinthodonts and crocodyliformes. Two orders of modern amphibians - tailed and legless (or worms) - probably originated from other branches of stegocephalians.
Reptiles originated from primitive amphibians, widely settling on land by the end of the Permian period thanks to the acquisition of pulmonary respiration and egg shells that protected them from drying out. Among the first reptiles, the cotylosaurs are especially notable - small insectivorous animals and active predators - therapsids, which gave way in the Triassic to giant reptiles, dinosaurs, which appeared 150 million years ago. years ago. It is likely that the latter were warm-blooded animals. Due to their warm blood, dinosaurs led an active lifestyle, which can explain their long dominance and coexistence with mammals. The reasons for the extinction of dinosaurs (approximately 65 million years ago) are unknown. It is assumed, in particular, that this could be a consequence of the mass destruction of dinosaur eggs by primitive mammals. The hypothesis according to which the extinction of dinosaurs is associated with sharp climate fluctuations and a decrease in plant food during the Cretaceous period seems more plausible.
Already during the period of the dominance of dinosaurs, there was an ancestral group of mammals - small-sized animals with fur that arose from one of the lines of predatory therapsids. Mammals are at the forefront of evolution thanks to such progressive adaptations as the placenta, feeding their offspring with milk, a more developed brain and the associated greater activity and warm-bloodedness. Mammals reached significant diversity in the Cenozoic, and primates appeared. The Tertiary period was the heyday of mammals, but many of them soon became extinct (for example, the Irish deer, the saber-toothed tiger, the cave bear).
The progressive evolution of primates turned out to be a unique phenomenon in the history of life, ultimately leading to the emergence of humans.
The most significant features of the evolution of the animal world were the following: 1) Progressive development of multicellularity and the associated specialization of tissues and all organ systems. A free lifestyle (the ability to move) largely determined the improvement of forms of behavior, as well as the autonomization of ontogenesis - the relative independence of individual development from fluctuations in environmental factors based on the development of internal regulatory systems. 2) The emergence of a hard skeleton: external - in arthropods, internal - in arthropods vertebrates. This division determined the different evolutionary paths of these types of animals. The exoskeleton of arthropods prevented an increase in body size, which is why all insects are represented by small forms. The internal skeleton of vertebrates did not limit the increase in body size, which reached its maximum in Mesozoic reptiles - dinosaurs and ichthyosaurs. 3) The emergence and improvement of the centrally differentiated stage of organocavities to mammals. At this stage, the separation of insects and vertebrates occurred. The development of the central nervous system in insects is characterized by the improvement of forms of behavior according to the type of hereditary consolidation of instincts. Vertebrates have developed a brain and a system of conditioned reflexes, and there is a pronounced tendency towards an increase in the average survival rate of individual individuals.
This path of vertebrate evolution led to the development of forms of group adaptive behavior, the final event of which was the emergence of a biosocial being - man.
Question 1. What is the value of Charles Darwin’s book “The Origin of Species”?
In his book On the Origin of Species, Charles Darwin first proposed a natural scientific explanation of evolution. He established the driving forces of the evolutionary process: hereditary variability and natural selection, which is based on the struggle for existence. Charles Darwin gave an explanation of the processes of speciation and the reasons for the diversity of species in nature.
Question 2. Why did Charles Darwin consider natural selection to be the main cause of evolution?
According to the evolutionary teachings of Charles Darwin, natural selection is understood as a process as a result of which individuals with hereditary characteristics that are useful in the given conditions of existence survive and leave behind offspring. On the other hand, individuals with hereditary traits that are harmful under given conditions die or do not leave offspring. The conditions in which any type of living being lives cannot always remain unchanged. Which trait is beneficial for the species and which is harmful is determined through the process of natural selection. Thus, it is natural selection that is one of the main factors in the formation of new species, i.e., the evolutionary process.
Question 3. What does the concept of “struggle for existence” mean? Support your explanation with examples.
Question 4. Is it possible to say that heredity and variability are inherent in all animals?Material from the site
Yes. All species of animals give birth to offspring similar to their parents, which indicates the presence of heredity - the ability of organisms to pass on their species and individual characteristics or properties to their descendants. On the other hand, in nature there are no two absolutely identical animals, the descendants are slightly different from their parents, this indicates the existence of variability - the ability of organisms to exist in different forms, responding to environmental influences.
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- Charles Darwin about the reasons for the evolution of the animal world 7th grade lesson
- Why did Charles Darwin consider natural selection to be the main cause of evolution?
The skull of Ichthyostega was similar to the skull of a lobe-finned fish Eusthenopteron, but a pronounced neck separated the body from the head. While Ichthyostega had four strong limbs, the shape of its hind legs suggests that this animal did not spend all its time on land.
The first reptiles and the amniotic egg
Hatching of a turtle from an egg
One of the greatest evolutionary innovations of the Carboniferous period (360 - 268 million years ago) was the amniotic egg, which allowed early reptiles to move out of coastal habitats and colonize dry areas. The amniotic egg allowed the ancestors of birds, mammals and reptiles to reproduce on land and prevent the embryo inside from drying out, so they could survive without water. This also meant that, unlike amphibians, reptiles could produce fewer eggs at any given time as the risks of hatchlings dying were reduced.
The earliest date for the development of an amniotic egg is about 320 million years ago. However, reptiles did not experience any significant adaptive radiation for another 20 million years or so. Modern thinking is that these early amniotes still spent time in the water and came ashore primarily to lay their eggs rather than feed. Only after the evolution of herbivores did new groups of reptiles emerge capable of exploiting the abundant floristic diversity of the Carboniferous period.
Gilonomous
Early reptiles belonged to an order called captorhinids. Hylonomus were representatives of this order. They were small animals about the size of a lizard, with amphibian skulls, shoulders, pelvises and limbs, as well as intermediate teeth and vertebrae. The rest of the skeleton was reptilian. Many of these new "reptilian" features are also seen in small, modern amphibians.
First mammals
Dimetrodon
A major transition in the evolution of life occurred when mammals evolved from a single line of reptiles. This transition began during the Permian period (286 - 248 million years ago), when a group of reptiles that included Dimetrodon gave rise to the "terrible" therapsids. (The other major lineage, the sauropsids, gave rise to birds and modern reptiles). These mammalian reptiles in turn gave rise to cynodonts such as Thrinaxodon ( Thrinaxodon) during the Triassic period.
Trinaxodon
This evolutionary line provides an excellent series of transitional fossils. The development of a key feature of mammals, the presence of a single bone in the lower jaw (compared to several in reptiles), can be traced through the fossil history of this group. It includes excellent transitional fossils, Diarthrognathus And Morganucodon, whose lower jaws have both reptilian and mammalian articulations with the upper jaws. Other new features found in this lineage include the development of different types of teeth (a feature known as heterodontity), the formation of a secondary palate, and an increase in dentary bone in the lower jaw. The legs were located directly below the body, an evolutionary advance that occurred in the ancestors of dinosaurs.
The end of the Permian period was marked by perhaps the greatest. According to some estimates, up to 90% of species have become extinct. (Recent studies have suggested that this event was caused by an asteroid impact, which triggered climate change.) During the subsequent Triassic period (248 - 213 million years ago), survivors of the mass extinction began to occupy vacant ecological niches.
However, at the end of the Permian period it was dinosaurs, not reptilian mammals, that took advantage of the newly available ecological niches to diversify into dominant land vertebrates. In the sea, ray-finned fish began a process of adaptive radiation, which made their class the most species-rich of all vertebrate classes.
Classification of dinosaurs
One of the major changes in the group of reptiles that gave rise to dinosaurs was the posture of the animals. The location of the limbs has changed: previously they protruded on the sides, and then began to grow directly under the body. This had significant implications for locomotion as it allowed for more energy-efficient movements.
Triceratops
Dinosaurs, or “terror lizards,” are divided into two orders based on the structure of the hip joint: lizard-hipped and ornithischian. Ornithischians include Triceratops, Iguanodon, Hadrosaurs and Stegosaurs). Lizards are further divided into theropods (such as Coelophysis and Tyrannosaurus rex) and sauropods (such as Apatosaurus). Most scientists agree that they are from theropod dinosaurs.
Although dinosaurs and their immediate ancestors dominated the terrestrial world during the Triassic, mammals continued to evolve during this time.
Further development of early mammals
Mammals are advanced synapsids. Synapsids are one of the two great branches of the amniote family tree. Amniotes are a group of animals that are characterized by the presence of embryonic membranes, including reptiles, birds and mammals. The other major amniotic group, the Diapsids, includes birds and all living and extinct reptiles except turtles. Turtles belong to the third group of amniotes - Anapsids. Members of these groups are classified according to the number of openings in the temporal region of the skull.
Dimetrodon
Synapsids are characterized by having a pair of additional holes in the skull behind the eyes. This discovery gave synapsids (and similarly diapsids, which have two pairs of openings) stronger jaw muscles and better biting abilities than early animals. Pelycosaurs (such as Dimetrodon and Edaphosaurus) were early synapsids; they were reptilian mammals. Later synapsids included therapsids and cynodonts, which lived during the Triassic period.
Cynodont
Cynodonts had many characteristic mammalian features, including a reduced number or complete absence of lumbar ribs, suggesting the presence of a diaphragm; well developed canines and secondary palate; increased size of the dentition; openings for nerves and blood vessels in the lower jaw, indicating the presence of vibrissae.
By about 125 million years ago, mammals had already become a diverse group of organisms. Some of these would have been similar to today's monotremes (such as the platypus and echidna), but early marsupials (a group that includes modern kangaroos and possums) were also present. Until recently, placental mammals (the group to which most living mammals belong) were thought to have a later evolutionary origin. However, recently discovered fossils and DNA evidence suggest that placental mammals are much older, possibly evolving more than 105 million years ago.
Note that marsupials and placental mammals provide excellent examples of convergent evolution, where organisms that are not particularly closely related evolved similar body shapes in response to similar environmental influences.
Plesiosaurs
However, despite having what many consider to be "advanced" mammals were still minor players on the world stage. When the world entered the Jurassic period (213 - 145 million years ago), the dominant animals on land, sea and air were reptiles. Dinosaurs, more numerous and unusual than during the Triassic, were the main land animals; crocodiles, ichthyosaurs and plesiosaurs ruled the sea, and the air was inhabited by pterosaurs.
Archeopteryx and the evolution of birds
Archeopteryx
In 1861, an intriguing fossil was discovered in the Jurassic Solnhofen Limestone in southern Germany, a source of rare but exceptionally well-preserved fossils. The fossil appeared to combine features of both birds and reptiles: a reptilian skeleton accompanied by a clear impression of feathers.
While Archeopteryx was originally described as a feathered reptile, it has long been considered a transitional form between birds and reptiles, making the animal one of the most important fossils ever discovered. Until recently, it was the earliest known bird. Scientists recently realized that Archeopteryx bears more similarities to maniraptorians, a group of dinosaurs that includes the infamous Velociraptor from Jurassic Park, than to modern birds. Thus, Archeopteryx provides a strong phylogenetic link between these two groups. Fossil birds have been discovered in China that are even older than Archeopteryx, and other discoveries of feathered dinosaurs support the theory that theropods evolved feathers for insulation and temperature regulation before birds used them for flight.
A closer look at the early history of birds is a good example of the concept that evolution is neither linear nor progressive. The lineage of birds is disordered, and many "experimental" forms appear. Not all achieved the ability to fly, and some looked completely different from modern birds. For example, Microraptor gui, which appears to have been a flying animal and had asymmetrical flight feathers on all four limbs, was a dromaeosaurid. Archeopteryx itself did not belong to the lineage from which true birds evolved ( Neornithes), but was a member of the now extinct enantiornhis birds ( Enantiornithes).
The end of the dinosaur era
Dinosaurs spread throughout the world during the Jurassic period, but during the subsequent Cretaceous period (145 - 65 million years ago) their species diversity declined. In fact, many of the typically Mesozoic organisms, such as ammonites, belemnites, ichthyosaurs, plesiosaurs and pterosaurs, were in decline during this time, even though they were still giving rise to new species.
The emergence of flowering plants during the Early Cretaceous period caused a major adaptive radiation among insects, with new groups emerging such as butterflies, moths, ants, and bees. These insects drank nectar from flowers and acted as pollinators.
The mass extinction at the end of the Cretaceous period, 65 million years ago, wiped out the dinosaurs along with any other land animal weighing more than 25 kg. This paved the way for the expansion of mammals on land. In the sea at this time, fish again became the dominant vertebrate taxon.
Modern mammals
At the beginning of the Paleocene (65 - 55.5 million years ago), the world was left without large land animals. This unique situation was the starting point for a great evolutionary diversification of mammals, which were previously nocturnal animals the size of small rodents. By the end of the era, these representatives of the fauna occupied many of the free ecological niches.
The oldest confirmed primate fossils date back about 60 million years. Early primates evolved from ancient nocturnal insectivores, something like shrews, and resembled lemurs or tarsiers. They were probably arboreal animals and lived in or subtropical forests. Many of their characteristic features were well suited to this habitat: hands designed for grasping, rotating shoulder joints, and stereoscopic vision. They also had a relatively large brain size and clawed toes.
The earliest known fossils of most modern mammal orders appear over a short period during the early Eocene (55.5–37.7 million years ago). Both groups of modern ungulates, the Artiodactyls (the order that includes cows and pigs) and the Odd-toed ungulates (including horses, rhinoceroses, and tapirs), became widespread throughout North America and Europe.
Ambulocetus
At the same time as mammals diversified on land, they also returned to the sea. The evolutionary transitions that led to whales have been extensively studied in recent years, with extensive fossil finds from India, Pakistan and the Middle East. These fossils indicate a change from the land-based Mesonychia, which are the likely ancestors of whales, to animals such as Ambulocetus and primitive whales called Archaeocetes.
The trend towards a cooler global climate that occurred during the Oligocene epoch (33.7 - 22.8 million years ago) favored the emergence of grasses, which were to spread to extensive grasslands during the subsequent Miocene (23.8 - 5.3 million years ago ). This change in vegetation led to the evolution of animals, such as more modern horses, with teeth that could cope with the high silica content of grasses. The cooling trend has also affected the oceans, reducing the abundance of marine plankton and invertebrates.
Although DNA evidence suggests that hominids evolved during the Oligocene, abundant fossils did not appear until the Miocene. Hominids, on the evolutionary line leading to humans, first appear in the fossil record in the Pliocene (5.3 - 2.6 million years ago).
During the entire Pleistocene (2.6 million - 11.7 thousand years ago), there were about twenty cycles of cold ice ages and warm interglacial periods at intervals of about 100,000 years. During the Ice Age, glaciers dominated the landscape, spreading snow and ice into the lowlands and transporting vast amounts of rock. Because a lot of water was trapped in the ice, the sea level dropped to 135 m than it is now. Wide land bridges allowed plants and animals to move. During warm periods, large areas were again submerged under water. These repeated episodes of environmental fragmentation led to rapid adaptive radiation in many species.
The Holocene is the current epoch of geological time. Another term that is sometimes used is the Anthropocene because its main characteristic is global changes caused by human activities. However, this term can be misleading; modern people were already created long before the era began. The Holocene era began 11.7 thousand years ago and continues to this day.
Mammoths
When warming came on Earth, it gave way. As the climate changed, very large mammals that adapted to extreme cold, such as the woolly rhinoceros, became extinct. Humans, once dependent on these "mega mammals" as their main source of food, switched to smaller animals and began collecting plants to supplement their diet.
Evidence shows that around 10,800 years ago the climate underwent a sharp cold turn that lasted several years. The glaciers did not return, but animals and plants were few. As temperatures began to recover, animal populations grew and new fauna species emerged that still exist today.
Currently, the evolution of animals continues, as new factors arise that force representatives of the animal world to adapt to changes in their environment.
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