The first plant organisms arose in the will in very distant times. The first living beings were microscopically small lumps of mucus. Much later, some of them developed a green color, and these living organisms began to look like unicellular algae. Single-celled creatures gave rise to multicellular organisms, which, like single-celled organisms, arose in water. From unicellular algae, various multicellular algae developed.
The surface of the continents and the ocean floor have changed over time. New continents rose and previously existing ones sank. Due to hesitation earth's crust In place of the seas, land arose. The study of fossil remains shows that the plant world of the Earth also gradually changed.
The transition of plants to a terrestrial lifestyle, according to scientists, was associated with the existence of land areas that were periodically flooded and cleared of water. The receding water was retained in the depressions. They either dried up or filled with water again. The drainage of these areas occurred gradually. Some algae have developed adaptations for living outside of water.
The climate at that time on the globe was humid and warm. The transition of some plants from an aquatic to a terrestrial lifestyle began. The structure of these plants gradually became more complex. They gave rise to the first land plants. The oldest group of known land plants are psilophytes.
Development flora on Earth - a long-term process, which is based on the transition of plants from an aquatic to a terrestrial way of life.
Psilophytes already existed 420-400 million years ago, and later became extinct. Psilophytes grew along the banks of reservoirs and were small multicellular green plants. They had no roots, stems, or leaves. The role of roots was played by rhizoids. Psilophytes, unlike algae, have a more complex internal structure- presence of integumentary and conductive tissues. They reproduced by spores.
From psilophytes came bryophytes and ferns, which already had stems, leaves and roots. The heyday of ferns was about 300 million years ago during the Carboniferous period. The climate at this time was warm and humid. At the end of the Carboniferous period, the Earth's climate became noticeably drier and colder. Tree ferns, horsetails and club mosses began to die out, but by this time primitive gymnosperms appeared - descendants of some ancient ferns. According to scientists, the first gymnosperms were seed ferns, which later became completely extinct. Their seeds developed on the leaves: these plants did not have cones. Seed ferns were tree-like, liana-like and herbaceous plants. Gymnosperms originated from them.
Living conditions continued to change. Where the climate was more severe, ancient gymnosperms gradually died out and were replaced by more advanced plants - ancient conifers, then they were replaced by modern conifers: pine, spruce, larch, etc.
The transition of plants to land is closely connected not only with the appearance of such organs as stems, leaves, roots, but, mainly, with the appearance of seeds, a special method of reproduction of these plants. Plants that reproduced by seeds were better adapted to life on land than plants that reproduced by spores. This became especially clear when the climate became less humid.
On the growths developing from spores (in mosses, mosses, ferns), female and male gametes (sex cells) are formed - eggs and sperm. In order for fertilization to occur (after the fusion of gametes), atmospheric or groundwater is necessary, in which sperm move to the eggs.
Gymnosperms do not need free water for fertilization, since it occurs inside the ovules. In them, male gametes (sperm) approach female gametes (eggs) through pollen tubes growing inside the ovules. Thus, fertilization in spore plants is completely dependent on the availability of water; in plants that reproduce by seeds, this dependence is not present.
Angiosperms - descendants of ancient gymnosperms - appeared on Earth over 130-120 million years ago. They turned out to be the most adapted to life on land, since only they have special reproductive organs - flowers, and their seeds develop inside the fruit and are well protected by the pericarp.
Thanks to this, angiosperms quickly spread throughout the Earth and occupied a wide variety of habitats. For more than 60 million years, angiosperms have dominated the Earth. In Fig. 67 shows not only the sequence of appearance of certain plant divisions, but also their quantitative composition, where angiosperms have a significant place.
About a billion years ago, many green, brown and other algae already lived on the bottom of the World Ocean. Their progressive evolution led to the fact that some of them reached gigantic sizes, but remained aquatic creatures. This is explained not only by the lack of special protection from drying out in their bodies, but also by the peculiarities of sexual reproduction. As is known, in algae there is an alternation of generations: a diploid sporophyte, which reproduces by spores, and a haploid gametophyte, at the stage of which reproduction occurs with the help of gametes, the copulation of which requires an aquatic environment. This is what became the main obstacle to the algae reaching land.
It is believed that the need to adapt to a terrestrial lifestyle has become the main focus evolution of plants. This was achieved by increasing the duration of the sporophyte stage and gradually reducing the gametophyte phase and, over time, its reduction in general. It was aromorphosis associated with the reduction of the gametophyte in seed plants that allowed them to develop a new adaptive space - land and create a diversity of species here. The plant world now numbers about half a million species, of which flowering plants accounts for more than half - about 300 thousand species.
Bryophytes are considered the most primitive higher plants preserved on Earth. They already have some division of the body into a stem and rhizoids, although they do not yet have a conducting system. Mosses evolved from algae at the very beginning of the Phanerozoic about 600 million years ago. From the spores they develop the so-called pre-escape, very similar to algae, and from it - the body of moss - the gametophyte. Copulation of gametes occurs only in water, which they accumulate in the axils of the leaves. Therefore, mosses can only live in damp, shaded places. A sporophyte is formed from the zygote, which develops directly on the gametophyte (Fig. 223). Unlike the gametophyte, the sporophyte is drought-resistant, which allowed mosses to reach land. Thus, they are not true land plants, but amphibians. Perhaps that is why they turned out to be a blind branch in the evolution of plants.
All other higher plants originated from rhiniophytes(Fig. 224, 225), which gave rise to green or brown algae in the Silurian period 400-500 million years ago. Mops, horsetails, ferns and gymnosperms diverged from them as separate evolutionary branches. This evolutionary explosion occurred in the Devonian period about 300-400 million years ago. Ferns became the first plants to truly conquer land, forming real forests in the Carboniferous period.
Due to the need to live on land, plants developed a conducting system, and integumentary and mechanical tissues were improved. From gymnosperms, angiosperms were formed at the border of the Mesozoic and Cenozoic. The appearance of angiosperms was marked by a number of aromorphoses: the appearance of a flower, the formation of internal and double fertilization, protection of the embryo from unfavorable conditions, and providing it with food in the early stages of development. Material from the site
During the evolution of angiosperms, the flower underwent the greatest changes. This is largely due to the plant's adaptation to pollination by wind or insects. In the latter case, the flowers are usually large, bright, with abundant pollen and fragrant nectar, and very often have a specialized pollinator ( remember: clover flowers can only be pollinated by bumblebees). This specialization, in turn, stimulates the evolution of insects. It is no coincidence that the beginning of the Cenozoic was marked by an outbreak of diversity in flowering plants and insects. This process of mutual evolution is called coevolution(from lat. co- together).
Main way plant evolution there was a decrease in the importance and duration of the gametophyte, which contributed to the emergence of plants on land and the subsequent formation of flowering plants.
On this page there is material on the following topics:
Patterns of biological evolution report
Report on the topic of evolution of higher plants
Report on the topic of plant evolution
Coevolution of higher plants
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The air-terrestrial habitat differs from the aquatic one. The density of water is greater than air. Therefore, the water seems to support the bodies in its thickness. On land, air cannot "hold" plants, and gravity would cause them to fall if land plants did not have strong mechanical tissues. There is no shortage of water in the aquatic environment; the plant can absorb it throughout the body. There is very little water in the air, and it is there in the form of vapor. The plant can no longer absorb it with its entire body. Therefore it was necessary to develop root system which absorbs water from the soil. To deliver water to other organs, a conduction system was required.
Thus, the emergence of plants on land gradually led to the formation of various tissues and organs. There was a specialization of body parts. The roots of the plant carry out soil nutrition by absorbing water with dissolved in it minerals. Leaves carry out aerial nutrition, synthesizing organic substances in the light. The stem ensures the movement of water and substances.
For a long time, only spore-bearing plants were terrestrial plants - mosses, ferns, horsetails and mosses. They need water to reproduce, so they cannot live everywhere on land.
About 250 million years ago, the Earth's climate became colder and drier. This led to the emergence of gymnosperms that could tolerate such conditions. Gymnosperms developed buds that were protected from unfavorable conditions by bud scales. Reproduction by seeds appeared, when water was no longer needed during fertilization. The sperm is delivered to the egg using a pollen tube. The seeds also have a supply of nutrients. Gymnosperms were able to colonize arid and cold habitats, and where spore plants lived, they gradually replaced them.
Angiosperms appeared about 150 million years ago. By this time, the climate on Earth had become even drier and warmer. Angiosperms are more adapted to living in complex and varied conditions due to their more complex structure. Plant tissues were improved and deciduousness appeared. Flower formation, different ways pollination, double fertilization, and fruit formation gave flowering plants advantages. The prevalence of vegetative propagation among flowering plants and its various methods made it possible to quickly occupy space.
Flowering plants and their animal pollinators (mostly insects) are closely related. Their evolution proceeded together, mutually determined. Plants and insects have adapted to life cycles each other.
Many plants that existed in earlier times have not survived to this day. Most of them became extinct because they turned out to be unadapted to the changed living conditions or were replaced by more adapted species. Some plants have been destroyed by humans. Extinct plants are studied by paleobotany. By studying plant fossils, scientists can trace them evolutionary path in time.
The book outlines current problem modern natural science- origin of life. It is written on the basis of the most modern data from geology, paleontology, geochemistry and cosmochemistry, which refutes many traditional but outdated ideas about the origin and development of life on our planet. Antiquity life and the biosphere, commensurate with the age of the planet itself, allows the author to conclude: the origin of the Earth and life is a single interconnected process.
For readers interested in geosciences.
Book:
<<< Назад Forward >>> Plants, as typical representatives of photoautotrophic organisms of our planet, arose during a long evolution, which originates from the primitive inhabitants of the illuminated zone of the sea - planktonic and benthic prokaryotes. By comparing paleontological data with data on the comparative morphology and physiology of living plants, it is possible to general view outline the following chronological sequence of their appearance and development:
1) bacteria and blue-green algae (prokaryotes);
2) cyan, green, brown, red, etc. algae (eukaryotes, like all subsequent organisms);
3) mosses and liverworts;
4) ferns, horsetails, mosses, seed ferns;
6) angiosperms, or flowering plants.
Bacteria and blue-green algae were found in the most ancient preserved deposits of the Precambrian; algae appeared much later, and only in the Phanerozoic do we encounter the lush development of higher plants: lycophytes, horsetails, gymnosperms and angiosperms.
Throughout the Cryptozoic period, predominantly single-celled organisms—various types of algae—developed in primary reservoirs in the euphotic zone of ancient seas.
The main representatives of prokaryotes discovered in the Precambrian had autotrophic nutrition - through photosynthesis. The most favorable conditions for photosynthesis were created in the illuminated part of the sea at a depth from the surface to 10 m, which also corresponded to the conditions of shallow-water benthos.
To date, the study of Precambrian microfossils has advanced, and accordingly, a large amount of factual material has been accumulated. In general, the interpretation of microscopic specimens is a difficult task that cannot be resolved unambiguously.
Trichome bacteria, which differ sharply from mineral formations of a similar shape, are best identified and identified. The obtained empirical material on microfossils allows us to conclude that they can be compared with living cyanobacteria.
Stromatolites, as biogenic structures of the distant past of the planet, were formed during the accumulation of a thin sediment of calcium carbonate captured by photosynthetic organisms of microbiological associations. Microfossils in stromatolites consist almost exclusively of prokaryotic microorganisms, mainly related to blue-green algae - cyanophytes. When studying the remains of benthic microorganisms composing stromatopites, one interesting feature of fundamental importance was revealed. Microfossils of different ages change little in their morphology and generally indicate the conservatism of prokaryotes. Microfossils related to prokaryotes remained almost constant for quite some time. for a long time. In any case, we have before us an established fact - the evolution of prokaryotes was much slower than that of higher organisms.
So, in the course of geological history, prokaryotic bacteria exhibit maximum persistence. Persistent forms include organisms that have been preserved unchanged during the process of evolution. As G. A. Zavarzin notes, since ancient communities of microorganisms show significant similarities with modern ones developing in hydrotherms and in areas of evaporite formation, this makes it possible to more thoroughly study the geochemical activity of these communities using modern natural and laboratory models, extrapolating them to the distant Precambrian time.
The first eukaryotes arose in planktonic associations of open waters. The end of the exclusive dominance of prokaryotes dates back to approximately 1.4 billion years ago, although the first eukaryotes appeared much earlier. Thus, according to the latest data, the appearance of fossil organic remains from black shales and carbonaceous formations of the Upper Lake region indicates the appearance of eukaryotic microorganisms 1.9 billion years ago.
From the date of 1.4 billion years ago to our time, the Precambrian fossil record expands significantly. The appearance of relatively large forms related to planktonic eukaryotes and called “acritarchs” (translated from Greek as “creatures of unknown origin”) is dated to this date. It should be noted that the Acritarcha group has been proposed as a vague systematic category denoting Microfossils of different origins, but similar in appearance morphological characteristics. Acritarchs from the Precambrian and Lower Paleozoic are described in the literature. Most acritarchs were probably single-celled photosynthetic eukaryotes - the shells of some ancient algae. Some of them could still have a prokaryotic organization. The planktonic nature of acritarchs is indicated by their cosmopolitan distribution in sediments of the same age. The most ancient acritarchs from the Early Riphean deposits of the Southern Urals were discovered by T.V. Yankauskas.
Over the course of geological time, the size of acritarchs increased. According to observational data, it turned out that the younger the Precambrian Microfossils, the larger they are. It is assumed that a significant increase in the size of acritarchs was associated with an increase in the size of the eukaryotic cell organization. They could have appeared as independent organisms or, more likely, in symbiosis with others. L. Margelis believes that eukaryotic cells assembled from pre-existing prokaryotes. However, for the survival of eukaryotes, it was necessary that the habitat be saturated with oxygen and, as a consequence, aerobic metabolism arose. Initially, free oxygen released during photosynthesis of cyanophytes accumulated in limited quantities in shallow water habitats. The increase in its content in the biosphere caused a reaction on the part of organisms: they began to populate oxygen-free habitats (in particular, anaerobic forms).
Data from Precambrian micropaleontology indicate that in the Middle Precambrian, even before the appearance of eukaryotes, cyanophytes constituted a relatively small part of the plankton. Eukaryotes needed free oxygen and increasingly competed with prokaryotes in those areas of the biosphere where free oxygen appeared. Based on available micropaleontological data, it can be judged that the transition from prokaryotic to eukaryotic flora of ancient seas occurred slowly and both groups of organisms coexisted together for a long time. However, this coexistence occurs in a different proportion in the modern era. By the beginning of the Late Riphean, many autotrophic and heterotrophic forms of organisms had already spread.
As they developed, organisms moved for nutrients to deeper and more distant areas of the sea. The fossil record notes a sharp increase in the diversity of large spheroidal forms of eukaryotic acritarchs in Late Riphean times, 900-700 million years ago. About 800 million years ago, representatives of a new class of planktonic organisms appeared in the World Ocean - goblet-shaped bodies with massive shells or outer covers mineralized with calcium carbonate or silica. At the beginning of the Cambrian period, significant shifts occurred in the evolution of plankton - a variety of microorganisms arose with a complex sculptured surface and improved buoyancy. They gave rise to true spiny acritarchs.
The appearance of eukaryotes created an important prerequisite for the emergence of multicellular plants and animals in the Early Riphean (about 1.3 billion years ago). For the Belta series from the Precambrian of the western states North America they were described by C. Walcott. But what type of algae they belong to (brown, green or red) is still unclear. Thus, the extremely long era of dominance of bacteria and related blue-green algae was replaced by an era of algae that reached a significant variety of shapes and colors in the waters of the ancient oceans. During the Late Riphean and Vendian, multicellular algae became more diverse; they were compared with brown and red algae.
According to Academician B.S. Sokolov, multicellular plants and animals appeared almost simultaneously. Various representatives of aquatic plants are found in Vendian sediments. The most prominent place is occupied by multicellular algae, the thalli of which often overflow the strata of Vendian sediments: mudstones, clays, sandstones. Macroplanktonic algae, colonial algae, spiral-filamentous algae Volymella, felt algae and other forms are often found. Phytoplankton is very diverse.
For most of Earth's history, plant evolution took place in aquatic environments. It was here that aquatic vegetation originated and went through various stages of development. In general, algae are a large group of lower aquatic plants that contain chlorophyll and produce organic matter through photosynthesis. The body of the algae has not yet been differentiated into roots, leaves and other characteristic parts. They are represented by unicellular, multicellular and colonial forms. Reproduction is asexual, vegetative and sexual. Algae are part of plankton and benthos. Currently, they are classified as a plant subkingdom Thallophyta, in which the body is composed of a relatively uniform tissue - thallus, or Thallus. The thallus consists of many cells that are similar in appearance and function. In the historical aspect, algae went through the longest stage in the development of green plants and, in the general geochemical cycle of matter in the biosphere, played the role of a giant generator of free oxygen. The emergence and development of algae was extremely uneven.
Green algae (Chlorophyta) are a large and widespread group of predominantly green plants, which falls into five classes. By appearance they are very different from each other. Green algae come from green flagellated organisms. This is evidenced by transitional forms - pyramidomonas and chlamydomonas, mobile unicellular organisms that live in waters. Green algae reproduce sexually. Some groups of green algae achieved great development during the Triassic period.
Flagellates (Flagellata) are grouped into a group of microscopic unicellular organisms. Some researchers attribute them to the plant kingdom, others to the animal kingdom. Like plants, some flagellates contain chlorophyll. However, unlike most plants, they do not have a separate cellular system and are able to digest food with the help of enzymes, and also live in the dark, like animal organisms. In all likelihood, flagellates existed in the Precambrian, but their undisputed representatives were found in Jurassic deposits.
Brown algae (Phaeophyta) are distinguished by the presence of brown pigment in such quantities that it actually masks chlorophyll and gives plants the appropriate color. Brown algae belong to benthos and plankton. The largest algae reach 30 m in length. Almost all of them grow in salt water, which is why they are called sea grass. Brown algae include sargassum algae - floating planktonic forms with a large number of bubbles. In fossil form they are known from the Silurian.
Red algae(Rhodophyta) have this color due to the red pigment. These are predominantly marine plants, highly branched. Some of them have a calcareous skeleton. This group is often called cullipora. They exist today, and have been known in fossil form since the Lower Cretaceous. Somipores, which are close to them, with larger and wider cells, appeared in the Ordovician.
Charovaya algae(Charophyta) are a very unique and rather highly organized group of multicellular plants that reproduce sexually. They are so different from other algae that some botanists classify them as leaf-stem algae due to the emerging tissue differentiation. Charodic algae are green in color and currently live in fresh water and in brackish water bodies. They avoid seawater with normal salinity, but it can be assumed that in the Paleozoic they inhabited the seas. Some charophytes develop spores impregnated with calcium carbonate. Characeae are among the important rock-forming organisms of freshwater limestones.
Diatoms(Diatomeae) - typical representatives of plankton. They have an oblong shape and are covered on the outside with a shell made of silica. The first remains of diatoms were found in Devonian sediments, but they may be older. In general, diatoms are a relatively young group. Their evolution has been studied better than other algae, since flint shells and valves of diatoms can be preserved in a fossil state for a very long time. In all likelihood, diatoms are descended from flagellates, which are yellow in color and are capable of depositing small amounts of silica in their shells. In the modern era, diatoms are widely distributed in fresh and marine waters, and are occasionally found in wet soils. Remains of diatoms are known in Jurassic deposits, but it is possible that they appeared much earlier. Fossil diatoms from the Early Cretaceous reached the modern era without interruption in sedimentation.
Very important event, which contributed to a sharp acceleration in the rate of evolution of the entire living population of our planet, was the emergence of plants from the marine environment onto land. The appearance of plants on the surface of the continents can be considered a true revolution in the history of the biosphere. The development of terrestrial vegetation created the prerequisites for animals to reach land. However, the massive transition of plants to land was preceded by a long preparatory period. It can be assumed that plant life on land appeared a very long time ago, at least locally - in a humid climate on the coasts of shallow bays and lagoons, where changes in water level periodically brought aquatic vegetation onto land. The Soviet naturalist L. S. Berg was the first to express the idea that the land surface was not a lifeless desert neither in the Cambrian nor in the Precambrian. The prominent Soviet paleontologist L. Sh. Davitashvili also admitted that in the Precambrian the continents probably already had some kind of population consisting of low-organized plants and, possibly, even animals. However, their total biomass was negligible.
To live on land, plants had to not lose water. It should be borne in mind that in higher plants - mosses, pteridophytes, gymnosperms and flowering plants, which currently make up the bulk of terrestrial vegetation, only roots, root hairs and rhizoids come into contact with water, while the rest of their organs are in the atmosphere and evaporate water the entire surface.
Plant life flourished most on the shores of lagoon lakes and swamps. Here a type of plant appeared, the lower part of which was in water, and the upper part in air environment, in direct sunlight. Somewhat later, with the penetration of plants onto non-flooded land, their very first representatives developed a root system and were able to consume groundwater. This contributed to their survival during dry periods. Thus, new circumstances led to the division of plant cells into tissues and the development of protective devices that did not exist in the ancestors that lived in water.
Fig. 14. Development and genetic relationships of various groups of land plants
The massive conquest of the continents by plants occurred during the Silurian period of the Paleozoic era. First of all, these were psilophytes - peculiar spore-bearing plants resembling club mosses. Some of the twisting stems of psilophytes were covered with bristly leaves. Psilophytes were devoid of roots, and mostly leaves. They consisted of branching green stems up to 23 cm high and rhizomes stretching horizontally in the soil. Psilophytes, as the first reliable sushi plants, created entire green carpets on moist soil.
Probably, the production of organic matter from the first land vegetation was insignificant. The vegetation of the Silurian period undoubtedly originated from the algae of the sea and itself gave rise to the vegetation of the subsequent period.
After the conquest of the land, the development of vegetation led to the formation of numerous and varied forms. Intensive separation of plant groups began in the Devonian and continued in subsequent geological time. The general pedigree of the most important plant groups is given in Fig. 14.
Mosses originated from. seaweed Their early stage of development is very similar to some green algae. However, there is an assumption that mosses originated from simpler representatives of brown algae, adapted to life on damp rocks or in soils in general.
On the surface of the Early Paleozoic continents, the age of algae gave way to the age of psilophytes, which gave rise to vegetation that was reminiscent in appearance and size of modern thickets of large mosses. The dominance of psilophytes was replaced in the Carboniferous period by the dominance of fern-like plants, which formed fairly extensive forests on marshy soils. The development of these plants contributed to the fact that the composition atmospheric air changed. A significant amount of free oxygen was added and a mass of nutrients necessary for the emergence and development of land vertebrates accumulated. At the same time, huge masses of coal were accumulated. The Carboniferous period was characterized by an exceptional flourishing of terrestrial vegetation. Tree-like mosses appeared, reaching a height of 30 m, huge horsetails, ferns, and conifers began to appear. During the Permian period, the development of terrestrial vegetation continued, which significantly expanded its habitats.
The period of dominance of ferns gave way to the period of cone-bearing conifers. The surface of the continents began to take on a modern appearance. At first Mesozoic era Conifers and cycads became widespread, and flowering plants appeared in the Cretaceous period. At the very beginning of the Early Cretaceous era, Jurassic forms of plants still existed, but then the composition of the vegetation changed greatly. At the end of the Early Cretaceous era, many angiosperms are found. From the very beginning of the Late Cretaceous era, they pushed aside gymnosperms and took a dominant position on land. In general, in the terrestrial flora there is a gradual replacement of the Mesozoic vegetation of gymnosperms (conifers, cycads, ginkgos) by vegetation of the Cenozoic appearance. The vegetation of the Late Cretaceous era is already characterized by the presence of a significant number of modern flowering plants such as beech, willow, birch, plane tree, laurel, and magnolia. This restructuring of vegetation prepared a good food base for the development of higher terrestrial vertebrates - mammals and birds. The development of flowering plants was associated with the flourishing of numerous insects that played an important role in pollination.
The onset of a new period in the development of plants did not lead to the complete destruction of ancient plant forms. Some organisms of the biosphere were preserved. With the advent of flowering plants, bacteria not only did not disappear, but continued to exist, finding new sources of nutrition in the soil and in the organic matter of plants and animals. Seaweed different groups changed and developed along with higher plants.
Coniferous forests, which appeared in the Mesozoic, still grow today along with deciduous ones. They provide shelter to fern-like plants, since these ancient inhabitants of the foggy and humid climate of the Carboniferous period are afraid of open places illuminated by the sun.
Finally, it should be noted that there are persistent forms in the modern flora. The most persistent were certain groups of bacteria, which remained virtually unchanged since the Early Precambrian. But from more highly organized forms of plants, genera and species were also formed, which have changed little to date.
It should be noted that there is an undoubted presence in the modern flora of relatively highly organized multicellular plant genera. Late Paleozoic and Mesozoic forms of plants, which lived without changes for tens and hundreds of millions of years, are, of course, persistent. Thus, at present, “living fossils” (Fig. 15) from groups of ferns, gymnosperms and clubmosses have been preserved among the plant world. The term “living fossil” was first used by Charles Darwin, citing the East Asian gymnosperm tree Ginkgo biloba as an example. From the world of terrestrial plants, living fossils include the most famous fern palms, ginkgo tree, araucaria, mammoth tree, or sequoia.
As noted by the expert on fossil flora A. N. Krshptofovich, many genera of plants, lords of ancient forests, also existed for an extremely long time, especially in the Paleozoic; for example, Sigillaria, Lepidodendron, Calamites - at least 100-130 million years. The same number - Mesozoic ferns 11 conifers Metasequoia. The genus Ginkgo dates back more than 150 million years, and modern look Ginkgo biloba, if you include the essentially indistinguishable form Ginkgo adiantoides, is about 100 million years old.
Living fossils of the modern plant world can otherwise be called phylogenetically conserved types. Plants that are well studied in paleobotanical terms and classified as living fossils are conservative groups. They have not changed at all or have changed very little compared to related forms of the geological past.
Naturally, the presence of living fossils in modern flora raises the problem of their formation in the history of the biosphere. Conservative organizations are present in all major phylogenetic branches and exist in the most different conditions: in deep and shallow sea zones, in ancient tropical forests, in open steppe expanses and in all bodies of water without exception. The most important condition for the existence of evolutionarily conservative organisms - the presence of habitats with a constant living environment. However, stable living conditions are not decisive. Presence only separate forms, and not all communities of flora and fauna, indicates other factors in the preservation of living fossils. The study of their geographical distribution indicates that they are confined to strictly defined territories, while geographical isolation. Thus, Australia, the islands of Madagascar and New Zealand are typical areas of distribution of terrestrial living fossils.
In its evolution, the plant world creates the general appearance of the ancient landscapes in which the development of the animal world took place. Therefore, the division of geological time can be carried out on the basis of the succession of various plant forms. The German paleobotanist W. Zimmermann, back in 1930, divided the entire geological past from the point of view of the development of the plant world into six eras. He gave them a letter designation and arranged them in sequence from ancient eras to younger ones.
A comparison of the usual geological time scale, constructed primarily from paleozoological data, with the plant development scale is presented in Table. eleven.
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