What happened during the Ordovician period. Ordovician period of the Paleozoic era: flora and fauna
This period was a time when invertebrates were still the undisputed rulers of the ocean floor. Some of them were able to move, others lived alone or in groups, being tied to the bottom. These sedentary or immobile animals collected food that was within their reach and did not require a developed brain. But life made more severe and demanding demands on moving animals. When searching for food, they relied on their senses and quick reactions to avoid attacks from other predators.
Found in South Africa in the early 1990s, the Promissum specimen was a giant conodont-bearing specimen, reaching 40 cm in length. Its bulging eyes indicate that it actively hunted for its prey.
Armed arthropods.
When the first arthropods appeared (in the beginning), their bodies were very small, and their shells (exoskeleton) were no thicker than a sheet of paper. But by the beginning of the Ordovician period, some arthropods developed shells that turned into real armor for protection against enemies. One of the groups of arthropods that had such shells and was numerous in the Ordovician period was the “horseshoe crabs”, or horseshoe crabs.
Despite the name, these animals were not actually crabs. They belonged to the chelicerates, which include spiders and scorpions. The front part of their body was protected by a dome-shaped shield, which completely hid the mouth opening and paws of these animals. The back of the body was protected by a second, smaller shield and ended in a long, sharp spike. Their shells are well preserved in sediment, but there is a much easier way to see these animals, because they have survived to this day. These are not the same species that existed in the Ordovician period, but over 400 million years these animals have changed very little.
They fed on small animals, using their claw-ended limbs to capture prey. These claws were hidden deep under the front shield of the body, which limited their size. Some close relatives of horseshoe crabs - eurypterids, or crustaceans, had claws pointed forward. During the Ordovician, most crustaceans were relatively small in size, but in the subsequent Silurian period they became the largest arthropods.
Arandaspis belonged to heterostracans, or heteroscutaneous fish-like creatures that did not have jaws. He moved in the water by moving his tail. It had no fins.
The first horseshoe crabs walked along the seabed on five pairs of legs. Today, five species of these "living fossils" exist on the east coast of North America and Asia.
Mysterious conodonts.
For more than a century, scientists have collected and cataloged scores of tiny tooth-like fossils that date back to Ordovician period or even considered even more ancient. They are known under the name conodonts because they are often cone-shaped. These formations obviously belonged to some kind of animal. Over time, the shape of conodonts changed. Almost every type of conodont corresponds to a specific time period, so geologists can determine the age of rocks by the appearance of the conodonts. Despite many years of searching, it was not possible to find the animals to which these conical miniature teeth belonged.
But in 1993, fossilized corpses of animals with conical teeth were found in Scotland. Then the same fossils were found in North America and South Africa. One of the species found is promissum. The mysterious animal had a thin, serpentine body and well-developed eyes. Some fossils contain traces of V-shaped muscles and notochord. This is already a feature of vertebrates and animals related to vertebrates.
Many scientists think that conodont-bearing animals were among the first vertebrates in the process of evolution. However, unlike other vertebrates from which four-legged animals evolved, conodont-bearing animals did not survive.
During the Ordovician period, something very unusual happened: an entirely new group of animals arose, one of very few to appear after the Cambrian extinction. These animals, called bryozoans, were tiny invertebrates protected by a skeleton made up of cells. They lived in colonies next to each other and their shape often resembled plants. Bryozoans turned out to be a very successful addition to the animal world and have not only survived to this day, but are also widespread.
Sea bottom Ordovician period was home to a variety of larger plant-like animals known as crinoids, or sea lilies. They belong to the same phylum of animals as the starfish, sea urchin; The sea lily has a long stem consisting of calcareous segments and a “crown” of fragile branching tentacles that grab food. Later, some crinoids moved from a static existence to a mobile lifestyle in the sea, where they not only wait for food, but search and fight for it. Currently, sea lilies attached to the bottom still exist in nature.
This Ordovician reef has been reconstructed from fossils found on the island of Newfoundland that are almost 500 million years old. Two nautiloids search the seafloor while trilobites and gastropods, or gastropods, crawl along the surface of the bottom below them. 1. Nautiloids with straight shells; 2. Nautiloids with spirally twisted shells; 3. Trilobites; 4. Gastropods; 5. Corals; 6. Sea lilies.
2.5.
2.6.
2.7.
Fauna of the Permian period
2.8.
2.9.
2.10.
Fauna of the Cretaceous period
2.11.
Fauna of the Paleogene period
2.12.
Fauna of the Neogene period
2.13.
2.3. Fauna of the Ordovician period
Ordovician period (490 - 443 million years ago)
Ordovician period - Ordovician, second period Paleozoic era geological history of the Earth. The Ordovician period follows from the Cambrian and overlaps the Silurian period. The beginning of the Ordovician system is determined by radiological methods to be 490-500 million years ago, and the duration was approximately 60 million years.
Rice. 2.3.1. Seabed of the Ordovician period. The marine fauna was characterized by such a wealth of forms that the Ordovician period seems to us to be the most important era in the entire history of the Earth. It was in the Ordovician that the main types of marine organisms were formed. Life in the Ordovician seas (Fig. 2.3.1) was even more diverse than in the Cambrian seas.
In the Ordovician period, the first fish appeared, but most of the inhabitants of the sea remained small - few of them grew to a length of more than 4-5 cm. The formation of hard covers in many animals meant that they acquired the ability to rise above bottom sediments and feed in food-rich areas waters above the seabed.
During the Ordovician period, more and more animals appeared that extracted food from seawater. Some groups of invertebrates reached their peak during this period, while other groups only began to develop more luxuriantly. In general, the evolution of the organic world at this time advanced so much that vertebrates appeared in the later Ordovician. From echinoderms(3, 4 Fig. 2.3.1) sea bubbles(MITROCYSTELLA, DENDROCYSTITES, ARISTO-CYSTITES, ECHINOSPHARITES and others) reached the peak of their development at this time. For the first time, representatives of another class of echinoderms appeared in large numbers - sea lilies CRINOIDEA - 2, fig. 2 .3 .1), probably descended from more ancient sea bubbles. If in the Cambrian crinoids were not widespread and did not have such beautiful forms as in later seas, in the Ordovician seas they were one of the best decorations. Their body, covered with plates that formed regular corollas, was attached to the bottom with the help of a long movable stem, consisting of a large number of ring-shaped segments. Around the mouth opening there was a crown of movable, sometimes branching arms - rays. With long flexible rays coated with an adhesive substance, sea lilies caught food particles from the water. Some species had up to 200 such rays. Sea lilies, like their stemless relatives - starfish - have safely survived to this day. Sea lilies often formed beautiful underwater thickets. And if we imagine that over the cup-shaped bodies of sea lilies, which strongly resembled buds or flowers and swayed on long stems, swam flocks of transparent bell-shaped or hat-shaped jellyfish with ribbon-shaped tentacles, then we can say with confidence that the beginning of to exist on our Earth is what we call beauty. Brachiopods(Fig. 2.3.2) in the Ordovician a number of new families, genera and species were formed, and at the beginning of this period forms with calcareous shells and with a lock already predominated (CLITAMBONITES, PORAMBONITES, ORTHIS and others). The most common owners of shells were oyster-like brachiopods, reaching a size of 2 - 3 cm.
Gastropods And elasmobranch molluscs were represented by a significant number of genera and species.
Rice. 2.3.4. The structure of an ammonite. In the Ordovician seas, the first significant development of four-branched cephalopods took place, a characteristic feature of which is the presence of a multi-chambered shell; these are all primitive representatives nautiloids rice. 2.3.3 (NAUTILOIDEA), the oldest forms of which we already see in the Cambrian seas (VOLBORTHELLA) and the last endangered genus of which, the little boat (NAUTILUS), still lives in four species at considerable depths in the Indian Ocean. The shells of Ordovician nautiloids, in contrast to the horn-like curved shells of modern nautilus species, were straight or conical; in the last, living chamber, the animal itself was placed; the remaining chambers, separated from each other by partitions, were filled with air or gas, due to which the entire shell represented a hydrostatic apparatus. Each partition had a hole with a tube-shaped edge. Through these holes passed, starting in the initial chamber of the shell, a special cord-like process of the animal’s body, the so-called siphon. The purpose of the siphon has not yet been precisely established; Apparently, it served to firmly connect the animal with the shell and allowed it to be controlled. These cephalopods (ENDOCERAS, ORTHOCERAS, etc.) were predators that plundered the Ordovician seas. The greatest heights of development were reached in the Ordovician seas and trilobites, which had very different body sizes and shapes (ASAPHUS, ILLENUS, CYCLOPYGE with hypertrophied eyes, CRYPTOLITHUS, with a wide horseshoe-shaped border along the edge of the head shield, DALMANITINA, SELENOPELTIS, with large spines on the head shield and body segments).
A completely new group of animals appeared in the Ordovician seas graptolites(Fig. 2.3.5). They evolved very quickly and, leading a mainly planktonic lifestyle, were very widespread. Graptolites formed bush-like or ribbon-like colonies, which in one group (DENDROIDEA) were widely attached to floating algae (less often they were attached to the seabed), and in the second group (GRAPTOLOIDEA) they swam directly at the surface of the sea with the help of special swim bladders, or with a long thread attached to algae. Each individual of these small animals was placed in a tubular cell made of flexible chitin.
Graptolites reproduced by budding and thus created colonies. Previously, graptolites belonged to the coelenterates, but now, based on the research of the Polish paleontologist R. Kozlovsky, they are classified as pterobranchs (PTEROBRANCHIA), which, together with the coelenterates (ENTEROPNEUSTA), form in many respects a highly organized group of invertebrates, the so-called hemichordates. Graptolites became completely extinct by the end of the Paleozoic, but in the modern fauna there are animals that are their distant relatives. These include, for example, RHABDOPLEURA NORMANNI, living in the North Sea.
Colonies of older graptolites were bush-like. In the process of their evolution, the number of branches was gradually reduced to two. These branches branched off to the side or formed a fork; at a later time they began to bend upward in the direction of the thread until the latter was included between them. Thus, the so-called two-row types of graptolites arose. Later (in the Silurian), one row of cells disappeared and single-row graptolites arose. At this stage of development, the graptoloid graptolites became extinct. Only bush-like and pound-shaped forms of dendroid graptolites existed until the Carboniferous. Of the Ordovician graptolites, the following are important: DICHOGRAPTUS - with eight branches, TETRAGRAPTUS - with four branches, DIDYMORGRAPTUS - with two fork-shaped branches, DICELLOGRAPTUS - with two branches bent upward, PHYLLOGRAPTUS - with four mutually sprouting branches, two-row DIPLOGRAPTUS and others.
Rice. 2.3.6. Bryozoans. At that time, another strange group of colonial animals appeared, helping stromatoporoids and corals to build reefs. These were bryozoans(BRYOSO.E), inhabiting the seas in amazing diversity to this day Fig. 2.3.6. Some bryozoans formed fine, finely netted bushes with regular cells, which old Czech slab-breakers aptly called “laces.”
An important event in the Ordovician seas was also the appearance corals(ANTHOZOA), belonging to three different groups. The first of these were four-rayed corals (TETRACORALLA), also characteristic of all subsequent seas of the Paleozoic, in which they played the same role with the later, six-rayed corals (HEXACORALLA), which originated from them, replaced them in the seas, starting from the beginning of the Mesozoic and live to this day. These corals differ from each other mainly in that in four-rayed corals the number of partitions and tentacles is a multiple of four, while in six-rayed corals it is a multiple of six. Corals were solitary or formed colonies. The second group of corals, the so-called tabulata (TABULATA), always created colonies of the most varied shapes, in which each polyp built a solid calcareous skeleton, separated by numerous transverse partitions - bottoms (TABULA). The last group of corals of the Ordovician seas were the so-called heliolitids, which also formed colonies of various shapes, sometimes reaching several meters in size.
Rice. 2.3.7. Arandaspis prionotolepis (from the Arandaspid group) fig. Wikipedia Fragmentary remains of a jawless fish have been discovered in sandstones near Harding, Colorado. The age of these layers was about 450 million years. Other interesting vertebrate remains were recovered from the same rocks, including the scales of a gnathostome, a shark-like predator equipped with jaws. The oldest fossils whose remains were well preserved were Sacabambaspida, found in Bolivia, and Arandaspida from Australia (Fig. 2.3.7).
Fossil evidence shows that the jawless species of the Ordovician period were very different from the few jawless species that exist today - lampreys and hagfishes. Their bodies and heads were covered with tough, leathery plates consisting of a bone-like substance. Only scaly tails had the flexibility necessary for swimming. Having neither jaws nor teeth, they were forced to feed on small foods that were found in large quantities, such as planktonic microorganisms.
Rice. 2.3.8. Conodonts Some of the very first animals to have teeth were conodonts ( Fig.2.3.8) appeared at the end of the Cambrian. The group of conodonts combines fossil skeletal elements belonging to various types of animals - protoconodonts , paraconodonts And euconodonts . The animals themselves are now also called conodont carriers(Conodontophora). They were eel-like creatures whose mouthparts consisted of 15 or, less commonly, 19 elements and were radically different from the jaws of modern animals. The shape of the elements is tooth-shaped, comb-shaped, leaf-shaped; composition - calcium phosphate. Among the conodont-bearing species there were both very tiny (about 1 cm long) and gigantic ones (for example, Promissum, whose length reached 40 cm). Currently, paleontologists agree that conodont-bearing organisms are characterized by the presence of large eyes, fins with fin rays, a notochord, and powerful transverse muscles.
Rice. 2.3.9. Sea world of the Ordovician. According to researchers, the “teeth” of some conodonts were like filtering devices, with the help of which plankton was filtered from the water and sent into the pharynx. Other teeth, based on their structure, in their opinion, were intended to “grab and tear flesh.” The lateral position of the eyes of conodonts, however, makes it unlikely that they had a predatory lifestyle. Preserved muscle prints suggest that some conodonts (Promisums, in any case) were skilled swimmers, however, incapable of rapid throws.
The amazingly diverse marine life of the Ordovician (Fig. 2.3.9) - scientists count 600 different families of sea inhabitants - did not last long. The climate on the planet became colder and drier, and at the end of the period it turned into global glaciation, which caused the extinction of many species. The polar ice caps absorbed more and more ocean water, sea levels dropped by 330 m. The shallow seas of the continental shelf turned into arid plains, and the creatures that lived in these seas died, especially those who could not migrate anywhere from the seabed.
Fauna of the Ordovician period
<< Фанерозой. Животный мир кембрийского периода. Кембрийский взрыв <<
A.S. Antonenko
Sources: | 1. | Animal world. Ordovician |
2. | History of our planet. Ordovician | |
3. | Wikipedia | |
4. | History of our planet |
The Ordovician period began about 485 million years ago and lasted until about 440 million years ago. This period was identified by Charles Lapworth in 1879 and named after the Celtic tribe called the Ordovicians. Charles Lapworth identified this period because two of his colleagues disputed which strata some rocks in north Wales lay in. The followers of Adam Sedgwick believed that they belonged to the Cambrian period, and the followers of Roderick Murchison believed that they belonged to the Silurian period. However, Lapworth believed that these strata belonged to a separate period. However, this period was not recognized by official science until 1960. This year it was officially recognized by the International Geological Congress.
During the Ordovician period, life continued to evolve and became increasingly complex. Organisms formed communities that became increasingly complex and food chains became more intricate, far superior to those of the Cambrian period. The Ordovician period saw an explosion of life, although it did not receive as much attention from the scientific world as the Cambrian Explosion. During this time, the number of marine species quadrupled, and trilobites became extremely diverse. It was during this time that the first reef-forming corals arose.
Shellfish were another group of marine animals that thrived during this time. A number of different molluscs figured prominently, and these included bivalves, navitolid cephalopods and gastropods. During this time, the first jawed fish and the first star fish appeared. Scientists also believe that the first land plants appeared at this time.
Trilobites dominated the oceans during this period, and this ecosystem was gradually replaced by a more mixed one. An ecosystem in which a variety of different organisms thrived.
Organisms that include molluscs, bryozoans, brachiopods and echinoderms. However, during this time triobites continued to evolve. They acquired attributes that made them more successful in their environment. Adaptations that include chitinous scutes on their heads or spines on their bodies to protect themselves from predators.
This period came to an end with a series of extinctions of many animal species that mark the boundary between the Ordovician and Silurian periods. It ended approximately 447 - 444 million years ago. During this time, about half of all faunal genera would disappear, and many groups would decline significantly, including trilobites, brachiopods, and bryozoans.
During the Ordovician period, the Laurentian mainland broke up into four large and a number of smaller islands. In place of the Russian continent, two large islands were formed, separated by a narrow strait. Almost half of the territory of the Siberian and Chinese continents was flooded by a shallow sea. In the southern hemisphere, a huge continent was formed - Gondwana, which included modern South America, the southern part of the Atlantic Ocean, Africa, the Indian Ocean, Australia, and Northern Asia. The Northern Tien Shan, Altai, Australian Cordillera, and West Siberian ranges begin to form. In the sea basins that existed in the Urals, Chukotka and Cordillera, thousands of volcanoes were active, producing powerful deposits of volcanic rocks.
Organic world
The algae underwent almost no changes during this period. The marine fauna was characterized by such a wealth of forms that the Ordovician period seems to us to be the most important era in the entire history of the Earth. It was in the Ordovician that the main types of marine organisms were formed.
Compared to the Cambrian, the number of trilobites increases significantly. In the Ordovician, many large trilobites (up to 50-70 cm) also appear in Europe. This indicates that they felt good in the new conditions. Thanks to the migration of fauna from west to east and adaptation to new conditions, 77 new genera of trilobites appear in the Ordovician seas.
All the most important groups of animals that lived in the seas at a later time were found in Ordovician deposits. In the loose green sandstones near Leningrad, many foraminiferal cores are found. Radiolarium is found in black shales. (There should also be pictures here, they are named after animals).
The first corals, bryozoans and tabulates appeared. Brachiopods and blue-green algae, calcareous and brown algae are rapidly developing. There were representatives of almost all types and most classes of marine invertebrates. At the same time, jawless fish-like creatures appeared - the first vertebrates. Planktonic radiolarians and foraminifera lived in the water column of oceans and seas; The graptolites reached their peak. Numerous and diverse trilobites, brachiopods, echinoderms, bryozoans, sponges, elasmobranchs, gastropods and cephalopods lived on the bottom of shallow seas, in coastal zones and on shallows. Corals and other coelenterates lived in warm-water seas.
At the end of the Ordovician period, some fish developed jaws and became active predators. Scientists believe that some of the rigid arches that supported the gills gradually turned into jaws, and teeth were formed from the plates surrounding the mouth opening. One of the new groups - the so-called placoderms (plate-skinned fish) - included the largest marine fish of that period, including the ferocious predators Dunkleostea, up to 3.3 m long. In the upper jaw, instead of teeth, they had rows of small plates. Constantly in contact with the lower jaw, these plates sharpened its edge so much that the fish were able to bite and crush prey with both jaws.
The Ordovician period, or Ordovician (485 - 444 million years ago) is one of the least known geological periods in the history of the Earth. It did not witness the same burst of evolutionary activity that characterized the previous one; rather, it was a time when the earliest arthropods and vertebrates expanded their presence in the world's oceans. The Ordovician is the second period (542-252 million years ago), which was preceded by the Cambrian, and then it was replaced by and periods.
Climate and geography
During most of the Ordovician period, global climate conditions were as warm as during the previous Cambrian; the average air temperature in the world was about 50 ° C, and the water temperature in the seas reached 45 ° C. However, by the end of the Ordovician, the climate was much colder, as an ice cap formed at the south pole and glaciers covered the adjacent land areas. Plate tectonics has taken the Earth's continents to some strange places; for example, most of the land that later became Australia and Antarctica was in the northern hemisphere! These early continents were biologically significant: their coastlines provided protected habitats for shallow-water marine organisms.
Sea life
Invertebrates
During this period, the Great Ordovician Radiation occurred, an event of significant biodiversity (biodiversification) that was second only to the Cambrian Explosion in importance for the early history of life on Earth.
Over the course of about 25 million years, the number of marine organisms around the world increased significantly, with new species, trilobites, brachiopods and (early starfish) appearing. One theory is that the formation and migration of new continents helped maintain biodiversity along their shallow coastlines, although climatic conditions likely also played a role.
On the other side of the evolutionary coin, the end of the Ordovician period marked the first great thing in the history of life on Earth (or, let's say, the first for which scientists have sufficient fossil evidence). Changing global temperatures, accompanied by a sharp drop in sea level, destroyed a huge number of species, although the whole recovered quite quickly by the beginning of the next Silurian period.
Vertebrates
Almost everything there is to know about life during the Ordovician period lies in Arandaspis and Astraspis. These were two genera of the first jawless, lightly armored prehistoric fish, measuring 12 to 14 cm in length and vaguely resembling giant tadpoles. The bone plates of Arandaspis and its ilk later developed into true skeletons. Some paleontologists also believe that the numerous, tiny, worm-like conodonts found in Ordovician deposits are true vertebrates; if so, they may have been the first vertebrates on Earth to have teeth.
Vegetable world
As in the previous Cambrian, evidence of terrestrial plant life in the Ordovician is elusive. If land plants existed, they consisted of microscopic green algae floating on or below the surface of the water. However, it was not until after the Silurian period that the first land plants of which there is hard fossil evidence appeared.