The first land animals. What were the first animals to come out of the water? The most ancient people - Omo

At the beginning of the next, Silurian period (or Silurian ) seas and continents retained approximately the same outlines as in the Cambrian. The marine fauna of the Silurian resembles the Cambrian, but appear and new groups of invertebrates - corals, graptolites, worms, bryozoans, sea ​​urchins.

Fauna and flora of the late Paleozoic (click to enlarge)

Corals belong to the type of so-called coelenterates - exclusively aquatic organisms. In addition to corals, coelenterates also include the well-known jellyfish and hydra. Corals still exist today; many of them are reef-formers in the tropical Pacific and Indian Oceans. Corals are structured very simply. Like other coelenterates, their body has only one internal cavity, representing the intestine (which is why they are called coelenterates). Externally, the body of the coral, or rather, coral polyp, represents a sac that opens outward (at the top) with a mouth opening, around which there is a corolla of tentacles that help capture prey. Coral polyps feed on small floating organisms - plankton. Through mouth opening Waste products are also thrown away. The body of a coral polyp is enclosed in a skeleton - a calcareous chamber secreted by the walls of the polyp. As the chamber is built up, the polyp itself rises higher and higher, the lower wall of which (the bottom of the sac) deposits horizontal partitions called bottoms.

Coral polyps can live alone (solitary corals) or in groups (colonial corals). Single corals reach sizes of 15-20 cm. Like colonial corals, they grow motionless to the bottom. All corals are inhabitants of the sea. They live in a warm clear water, oxygen-rich and well-lit, that is, no deeper than 45 m.

Peculiar animals - graptolites . They are known from Silurian deposits - the so-called graptolite shales, common here near Leningrad, in the Baltic states and in Central Asia, and in Western Europe- in England, Germany and Sweden. Graptolites look like fan-shaped threads or twigs, on the sides of which there are numerous tiny polyp cells. At the top, where the ends of the threads met, during the life of the graptolites there was an air-bearing bell, the imprints of which have been preserved. Probably, the graptolites were either passively swimming animals, or some of them crawled along the bottom. Graptolites are classified as hemichordates.

Bryozoans, as the name suggests, resemble plants (mosses) rather than animals. Bryozoans form colonies that look like crusts and deposits on underwater rocks or twigs similar to coral. Like coral polyps, each bryozoan sits in a separate cell, but bryozoans are more highly organized animals than corals. Their intestinal-digestive tract has not only an inlet, but also an outlet; in addition, they already have a real nervous system(and in corals - only individual nerve cells).

The mouth opening of the bryozoan, like that of corals, is surrounded by a corolla of tentacles, the movement of which forces food into the mouth - unicellular algae and unicellular animals. Interestingly, some individuals of bryozoans have the appearance of flagella that continuously vibrate, or bird-like heads that constantly clap their “beaks.” This is a “guard” that drives away the enemies of bryozoans, and at the same time they are purifiers of silt. Bryozoans have never been a particularly numerous group, but some of their orders have survived to the present day.

With their spines, sea urchins resemble real urchins - land mammals, but have no relationship with them. The body of the sea urchin is enclosed in a spherical calcareous shell, consisting of many plates. These plates form fields, some of which carry needles, while others have tiny holes. Through such holes protrude hundreds of microscopic legs in the form of soft tubes filled with water. Water is pumped into them through special channels inside the animals’ bodies. With the help of its legs, the hedgehog moves slowly or sticks tightly to some underwater object. The movement of the sea urchin also involves spines, which also serve for protection. Some sea urchins reached the size of a child's head. Modern sea creatures are found in our northern and eastern seas. They feed on algae and small animals.
In the area of ​​the present Scandinavian Peninsula, in Scotland and Ireland, in the place of Spitsbergen and along the eastern coast of Greenland - where the sea existed for many millions of years - high mountain ranges. Their remains are the Scandinavian Mountains, the Grampian Mountains of Scotland, folded layers along the eastern edge of Greenland and the island of Spitsbergen. In the second half of the Silurian, powerful mountain-building movements took place - the so-called Caledonian folding.

The mountainous land rose in the region of present-day Kazakhstan and the northern ranges of the Tien Shan, and the Sayan-Baikal mountain arc was formed.

The Caledonian orogeny led to the rise of continents and the gradual shallowing of the seas, the appearance of numerous small bays and lagoons. Some of them were desalinated by the rivers flowing into them, in others the salinity of the water increased and even the deposition of salts occurred.

Most marine animals cannot tolerate changes in the salinity of sea water in either direction. Therefore, only a few of the inhabitants of the Silurian Sea adapted to life in lagoons.

The “cramped living space” of the maritime population served as an impetus for the development of land as a new additional area of ​​​​life. It was from the dying areas of the sea - lagoons - that first plants began to emerge on land, and then animals that fed on these plants, and only later predatory animals came to land.

In the Silurian, land plants - psilophytes - have already been distributed; Apparently they originated from algae, most likely from green ones.

Their body, like algae, is not yet divided into the main organs - root, stem and leaves. Instead of roots, they had peculiar underground single-celled outgrowths - rhizoids. The most primitive of the psilophytes did not even have a stem that would bear true leaves. Psilophytes reproduced with the help of spores placed in sporangia - at the ends of branches. Some psilophytes were swamp plants, while others were true land inhabitants, sometimes reaching significant sizes - 3 m in height. Psilophytes did not last long. They are known back in next period- Devon. Many paleobotanists include two more modern genera among them. tropical plants- psilots. In the Silurian, another group of plants (also apparently descended from algae) was widespread - mushrooms, which may have first been aquatic forms and then came to land. In the same period, there were also more highly organized plants - fern-like plants, in particular primitive lycophytes. Scorpions appear in Silurian. These ancient scorpions may not have yet been terrestrial animals, but first inhabited various bodies of water - rivers, lakes and swamps.

And another remarkable event occurred in the Silurian: the first vertebrates appeared - the so-called armored fish, the remains of which are found together with giant crustacean scorpions. Both of them were inhabitants of lagoons - loosened bays of the sea. Probably, armored fish, and after them their enemies - giant crustacean scorpions, climbed up the river deltas, gradually mastering fresh waters.

There are still two points of view on the question of where the first vertebrates appeared - in the seas or rivers. IN sea ​​water contains a lot of dissolved calcium, and calcium is part of animal bones; in addition, all lower vertebrates live in the sea. This is compelling evidence in favor of marine origin vertebrates. But supporters of the theory of freshwater origin believe that the skeleton should have appeared in rivers where there is a current: the skeleton is a stable support for the body, necessary to counteract the movement of water.

One thing is certain: the ancestors of vertebrates lived in an area where fresh waters bordered with sea waters, and their remains are found there. The most ancient vertebrates known to us already possessed bone tissue - a shell, but their internal skeleton was, apparently, cartilaginous (it is not preserved in the fossil state). The replacement of cartilage with bone and its ossification occurs much later - in higher groups of fish. Ancient armored fish were not yet real fish, they only had a fish-like shape. This body shape - in the form of a torpedo - is generally characteristic of actively swimming aquatic animals, since it provides the least resistance when moving in water.

Ancient armored fish belong to the group of so-called jawless fish, which are contrasted with gnathostomes, which include other classes of vertebrates.

Armored agnathans are known only from the Silurian and Devonian, but some agnathans have survived to the present day; these are lampreys and hagfishes. All jawless animals, as their name indicates, lacked jaws, as well as paired limbs (fins) and usually had only one nostril. Ancient jawless animals, the remains of which are often found in our Baltic states, on the Yenisei and in the Kolyma basin, as well as in Northern Europe And North America, were quite large animals - half a meter or more in length. Their body in the front part or almost entirely (except for the tail) was enclosed in a shell consisting of bone plates and scales. This armor protected them from dangerous pursuers - cancer scorpions, which reached a length of 3 m.

Armored jawless creatures fed on plankton. Probably some of the jawless ones were benthic forms. Poking their snouts into the mud, they stirred it up and caught small organic remains.

Thus, the Silurian was a period not only of the flourishing of various groups of invertebrates, but also the time of the appearance of the first vertebrates. In the Silurian, the settlement of land plants and the emergence of the first animals on land began.

The evolution of life on the planet began more than three billion years ago, some scientists say even more than four billion years. It was then that the first organized ecosystems arose, although these were microbes and bacteria, and mammals were still very far away. So what were the first animals on Earth?

The very first

The oldest traces of animal life on Earth are about a billion years old, and the oldest fossils of animals themselves are approximately 600 million years old.

The first animals that appeared on the planet were microscopically small and soft-bodied. They lived on seabed or in bottom silt. These creatures could not petrify, so the only indicator of their presence on Earth is the remains of their burrows or passages. The individuals were very resilient, and it was they who gave rise to the Ediacaran fauna - the first known animals on the planet.

Ediacaran fauna: light at the end of the Vendian tunnel

The Ediacara fauna gets its name from the Ediacara Hills, which are located in Australia. Here in 1946, unusual fossils were discovered that looked somewhat similar to modern jellyfish, worms and corals. They were small - on average 2 centimeters in diameter.

At first, scientists decided that the find dates back to the Cambrian period: it was then that the rapid development of the animal world began (approximately 570 million years ago). But with a more detailed study, it was possible to establish that these fossils are even older and belong to an earlier period - the Vendian. This was a real discovery, since no one knew for sure whether life existed during this period.

Then representatives of the Ediacaran fauna were found in different parts of the planet: in Namibia, Russia, Greenland. But despite the findings, biologists are still trying to understand what happened to them.

This is what one of these ancient animals, Kimberella, supposedly looked like:

Scientists believe that these are the direct ancestors of modern jellyfish and mollusks.

What did the Ediacarans look like?

The structure of the world's first animals was the simplest: they had no limbs, head, tail, mouth or digestive organs. The Ediacaran creatures weren't very good bright life)) at that time the planet was safe, there were no predators yet, so they didn’t even have anyone to defend themselves from.

It is assumed that they simply absorbed organic matter from the water with their entire bodies. Moreover, some of them formed a symbiosis with algae, and in appearance many of the creatures were very similar to plants.

For example, the largest creature was Dickinsonia.

Some individuals reached a meter in length, but usually did not exceed one centimeter in thickness. They had a flat, bilaterally symmetrical, grooved oval body. A kind of rug.

Scientists have not decided which group to classify it in: some consider it an ancestor of animals, some say that it is a type of mushroom, and others argue that it generally belonged to a class of creatures that do not exist today in the kingdom of nature. And her modern relatives were never discovered.

What happened after the world's first animals?

The next period in the history of the development of life on Earth is called the Cambrian. It began about 570 million years ago and lasted about 70 million years. It was here that an astonishing evolutionary explosion occurred, during which representatives of most of the main groups of animals known to the world first appeared on Earth. modern science. And this happened thanks to good climatic conditions.

During the Cambrian period, huge plumes and continental shoals existed on the planet. There were ideal conditions for life: a bottom covered with a layer of soft silt, and warm water. A lot of oxygen has already formed in the atmosphere (although much less than now). The development of hard land covers led to the emergence of new life forms, such as arthropods - the first arthropods.

Animals needed new ways to protect themselves from new highly organized predators. As a result of evolution, creatures developed means of defense, so predators had to develop new hunting methods to overcome the resistance of the prey.

During the Cambrian period, sea levels rose and fell repeatedly, species became extinct, and were replaced by others who had to adapt to new living conditions and methods of subsistence.

The animal world became more diverse, and more and more populations could exist next to each other without claiming the food resources of their neighbors.

To live on land, animals need lungs, which allow them to extract oxygen from the air. Without lungs, aquatic animals would suffocate and die immediately as soon as they reached the surface. But the moment came when many living beings learned to breathe atmospheric air.

Amphibians

The first animals to inhabit the land protruding from the water were amphibians. They never went far from the water because they laid eggs in the water to reproduce. Frogs living in ponds do exactly the same thing now.

These were:

1. Dolochosoma
2. Urocordilus

At the time when the first animals came out of the water, fish also changed greatly. Most of them have already become similar to modern fish.

Insects

The sound of wings has already begun to be heard in the ancient forests. These were some creatures, descendants of aquatic scorpion crabs and other species, who acquired wings and began to fly. This is how insects arose. There were no birds yet. The most ancient insects were dragonflies. Some of them had a wingspan of up to half a meter.

How were the first amphibians born?

It is possible that some fish acquired the ability to breathe on land for a short time when their ponds dried up. They crawled on the ground in search of water so as not to die. Some of them gradually learned to live on land.

Humanity owes the emergence of natural diversity on Earth to billions of years of revolution. Modern geologists and paleontologists have discovered turning points in the development of life on our planet.

1. The most ancient people - Omo

People can now trace their ancestry back hundreds of thousands of years. The two skulls, named Omo 1 and Omo 2, which were discovered in Ethiopia in 1967, are 195,000 years old, making them the earliest anatomically modern humans discovered so far. Now scientists think that Homo sapiens began to develop 200,000 years ago.

However, there is still debate on this issue, since evidence of cultural development is found musical instruments, needles and jewelry - date back only 50,000 years. Complex composite tools such as harpoons also appeared around this time. Therefore, no one can answer a simple question: if modern people appeared 200,000 years ago, why did it take them a full 150,000 years to develop anything resembling a culture.

2. The most ancient bird is Protoavis

Today, everyone knows that birds evolved from dinosaurs, and also that many dinosaurs were actually covered in feathers. As a result, the question “which bird is the most ancient” essentially needs to be reformulated into “at what point can dinosaurs begin to be considered birds.”

For a long time, paleontologists considered Archeopteryx to be the most ancient birds, but today an even more ancient candidate for the title of the first bird has emerged. Protoavis lived about 220 million years ago, 80 million years earlier than any of its competitors. The fossil was found in Texas by paleontologist Sankar Chatterjee, who argues that Protoavis is actually closer to modern birds than Archeopteryx.

3. The first types of creatures that began to walk on earth - Tiktaalik and Pneumodesmus

Tiktaalik, a duck-billed creature that lived in the Devonian period, was something between a fish, a frog and an alligator. It is believed that it first emerged from the water onto land 375 million years ago. Discovered in Canada in 2004, this species is considered an important transition between aquatic vertebrates and the first land animals. Tiktaalik also boasts ribs that can support its body out of water, lungs, a movable neck and eyes on the top of its head, like a crocodile. The centipede pneumodesmus lived about 428 million years ago. The 1-centimeter-sized creature was actually the first creature to live permanently on earth and breathe air.

4. The most ancient reptile - hylonom

Reptiles were the first vertebrates that could live on earth. The lizard-like creature Hylonom, which is only 20 centimeters long, is believed to be the oldest reptile. Hylonomas, which were apparently insectivores, arose approximately 310 million years ago. Preserved fossils of this creature were discovered in 1860 inside a tree trunk in Nova Scotia.

5. The oldest creature capable of flight is Rhiniognathus

Flying as a primary means of transportation requires complex design body (low body weight, but strong skeleton), as well as powerful wing muscles. The first creature that was capable of flight is actually the oldest known insect. Rhyniognatha hirsti is a tiny insect that lived about 400 million years ago. The first evidence of the existence of this insect was discovered in 1928 in Devonian rocks.

6. The first flowering plant - Potomacapnos and Amborella

People tend to associate plants with flowers, but flowers are actually relatively new. Before flowers existed, plants reproduced using spores for hundreds of millions of years. In fact, scientists do not even know why flowers arose, since they are very delicate and whimsical, and also require a huge amount of energy, which could theoretically be used much more rationally.

These incomprehensible circumstances led Darwin to describe the growth of flowers as " terrible secret"The oldest known fossils flowering plants refer to Cretaceous period, between 115 and 125 million years ago. Some of the oldest flowers are Potomacapnos, which surprisingly resembles a modern poppy, as well as Amborella, which was found on the island of New Caledonia. Everything indicates that flowers did not develop slowly, but suddenly arose in fact in their modern form.

7. The oldest mammal is Hadrocodium

Oldest famous mammal resembled a small mouse or a modern shrew. The length of Hadrocodium, the remains of which were found in China in 2001, was about 3.5 centimeters, and the animal weighed only 2 grams. Most likely, it led a lifestyle similar to a modern shrew, since its teeth were specialized fangs for crushing insects. Hadrocodium lived about 195 million years, long before some of the most famous dinosaurs, including Stegosaurus, Diplodocus, and Tyrannosaurus.

8. The first tree is Wattiesa

Trees played (and still play) a crucial role in shaping the Earth's atmosphere. Without them, carbon dioxide would not be converted into oxygen, and the planet would soon become lifeless. The first forests dramatically changed the Earth's ecosystem. Thus, the appearance of trees can be considered one of the most important evolutionary breakthroughs in history.

Currently, the oldest known tree is a 397-million-year-old species called Wattiesa. The leaves of this fern-like plant resembled a palm, and the tree itself reached a height of 10 meters. Wattiesa arose 140 million before the dinosaurs. The plant reproduced by spores, like modern ferns and mushrooms.

9. The oldest dinosaur is Nyasasaurus

Dinosaurs began to reign on Earth after the Permian mass extinction, which occurred about 250 million years ago and wiped out about 90 percent of all species on the planet, including 95 percent sea ​​life, and most of the planet's trees. After this, dinosaurs appeared in the Triassic.

The oldest dinosaur currently known is Nyasasaurus, whose bones were discovered in Tanzania in 1930. Until now, scientists have no idea whether he was a predator or a herbivore, and whether he walked on two legs or four. Nyasasaurus was only 1 meter tall and weighed 18-60 kg.

10. The Oldest Life Form

What is the oldest life form known to science? Quite a difficult question, since often the fossils are so ancient that their age is difficult to accurately determine. For example, rocks discovered near the Pilbara region of Australia contained microbes almost 3.5 billion years old. However, some scientists believe that such Precambrian organ-wall microfossils are actually a strange form of minerals that arose under special hydrothermal conditions. In other words, they are not alive.

This strange multi-legged creature was one of the first animals to walk on land.

Pioneers of life on land

The oldest known fossils of terrestrial invertebrates are 400 million years old. They are similar to scorpions and belong to a group of arthropods that have an articulated body covered with a shell that is well preserved in fossil form. It can be assumed that worms and some mollusks lived on land at that time, but their soft bodies are poorly preserved, so they did not leave any traces. Paleontologists believe that the true pioneers of land conquest appeared several million years earlier and that they were probably very close to modern tardigrades. These tiny animals, no more than 1 mm in length, swarm in thin films of water covering mosses and lichens. They are able to survive even if their habitat dries out: their body is almost completely dehydrated and remains viable for many years. Such an ability could allow these animals, regularly deprived of water, to be the first to gradually conquer land.

The first insects

During the Devonian period (400-360 million years ago) and the following Carboniferous period arthropods quickly spread on land. Appeared different groups animals: centipedes, soft-footed animals (animals similar to slugs, but with primitive legs), arachnids (resembling modern ticks). Some species reached significant sizes, such as giant centipede Arthropleura (1.8 m), the largest arthropod ever to exist on land. Despite its impressive appearance, this harmless animal ate only plants.
Before him, the first microscopic insects, collembolas, were a few tenths of a millimeter in size. These primitive wingless animals exist everywhere: they live under the bark of trees, under stones, in moss. Since the Carboniferous period, cockroaches and mayflies have been no different from their modern descendants. Although scorpions were among the first animals to set out to conquer land, for a long time(until the Carboniferous period) remained amphibians and lived without moving away from water.

Wings to fly

All these terrestrial arthropods were vegetarians and were deprived of wings until predators appeared, mainly spiders and scorpions, which were fully adapted to life on land. It was with the advent of these predators that insects acquired an excellent means of escaping from them - flight. For 50 million years, insects were the only animals capable of flight. Meganeura, a huge dragonfly with a wingspan of more than 70 cm, flew in the forests of the Carboniferous period.

Shell and limbs

Arthropleura is a giant centipede (1.8 m in length). Despite its terrifying appearance, it ate plants.

It is difficult to explain what caused the first invertebrates to leave the water. Perhaps persecuted sea ​​predators, they had no choice if they wanted to survive. However, life on land is hostile and difficult: the lack of water threatens animals with dehydration, the force of gravity presses them to the ground, and one must be able to breathe oxygen from the air, and not from water. But, according to scientists, the first terrestrial invertebrates had a double advantage: a shell that protected them from the effects of gravity, and limbs for movement. The muscles that control the limbs are attached to the shell. This shell (which insects call the cuticle) is waterproof and therefore prevents the animal from dehydrating. Thus, the shell allows animals to survive in dry places. Worms without shells are forced to burrow into damp soil.

Insects, masters of the Earth

It is believed that the Earth is most densely populated by mammals, which include humans. But the development of insect diversity has been even more successful. IN Mesozoic era(245-65 million years ago) insects were already very numerous, and in Cenozoic era the number of insect species has especially increased. Today, while mammals represent 3,600 species, the insect class numbers about 800,000, and it is estimated that 5 times more remain to be discovered. The bronze beetle (see photo) belongs to the group of Coleoptera insects, which includes 280,000 species (scarabs, ladybugs etc.).

How do insects breathe?

On the abdomen of this locust, a series of small holes can be distinguished: these are breathing holes called spiracles. Air enters through them and is directed to the cells of the body through tiny, very thin tubes - tracheas. This system is only effective for small animals. It allowed insects to colonize the land, but it also limited their growth. Spiders, scorpions, snails do not have tracheas, they breathe very simple lungs. The blood of insects serves only to transport nutrients and waste. Their blood is transparent because it does not contain the red pigment hemoglobin, which carries oxygen in the blood of vertebrates.
Some time after the plants, the first animals left the water to settle on land. These were invertebrate animals belonging to arthropods. Their body was covered with a shell, and they moved under water thanks to their jointed limbs. Gradually these animals came out of the water and learned to move on land. At first they lived in damp places, near ponds and rivers. Then they improved and began to venture further and further from the water. Finally, they grew, reaching impressive sizes.