The meaning of the CAMBRIAN PERIOD in the Encyclopedia of Biology
CAMBRIAN PERIOD
(Cambrian), first period Paleozoic era. Lasted approx. 35 million years. It began 540 million years ago and ended 505 million years ago. In this period huge continent Gondwanaland, located in the equatorial region, and several smaller land masses (on the site of modern Siberia, China, Europe and North America) were bordered by vast shallow seas. The cool climate at the beginning of the Cambrian (a consequence of the glaciation at the end of the Vendian) and the enrichment of the atmosphere with oxygen apparently led to a phenomenon called the “Cambrian evolutionary explosion”. It was expressed in the rapid increase in the diversity of marine multicellular organisms, many of which acquired a mineralized cover (shell, shell, tube, etc.) - calcareous, phosphate, chitinous or flint. These are trilobites, coelenterates, mollusks, echinoderms, graptolites, jawless fish-like creatures, etc. At the same time, a number of groups of animals arose, systematic position and whose family relationships remain unclear, similar in structure to arthropods, worms or crustaceans. Thus, all known types of animals appeared in the Cambrian, including chordates. In addition, quite a lot of soft-bodied multicellular organisms continued to survive, unknown family relations with known types of animals. Of the plants, the Cambrian is characterized by the appearance and wide distribution of lime-secreting algae, new reef-formers, together with archaeocyaths. The land was almost lifeless, populated only by bacteria and fungi, but by the end of the Cambrian the first worms and centipedes probably appeared. The richest and most famous localities of the Cambrian fauna are in Canada, Greenland, China and Russia (Aldan).
Encyclopedia Biology. 2012
See also interpretations, synonyms, meanings of the word and what the CAMBRIAN PERIOD is in Russian in dictionaries, encyclopedias and reference books:
- PERIOD in the Dictionary of Musical Terms:
(from Greek - bypass, certain circle time) - a construction in which a more or less complete musical thought is presented. sometimes in... - PERIOD
MEDIUM TERM - see MEDIUM TERM... - PERIOD in the Dictionary of Economic Terms:
INTEREST - see INTEREST... - PERIOD in the Dictionary of Economic Terms:
TAX - see TAX PERIOD... - PERIOD in the Dictionary of Economic Terms:
GRACE - see GRACE PERIOD... - PERIOD in the Dictionary of Economic Terms:
GRACEFUL - see GRACEFUL... - PERIOD in the Dictionary of Economic Terms:
BUDGET - see BUDGET... - PERIOD in the Literary Encyclopedia:
[Greek periodos - “detour”, “circle”] - a term introduced by Aristotle to designate “speech that has in itself a beginning and an end and ... - PERIOD in the Big Encyclopedic Dictionary:
in music, see Musical... - PERIOD in the Encyclopedic Dictionary of Brockhaus and Euphron:
A period is a period of time after which known events return in the same order. In astronomy it is used to mean the time of revolution of the planet or ... - PERIOD in the Modern Encyclopedic Dictionary:
(from the Greek periodos - bypass, rotation, a certain circle of time), 1) a period of time covering any completed process. 2) Stage social development, … - PERIOD
[from Greek bypass, rotation] 1) a period of time covering any completed process; 2) in astronomy, the period of time during which ... - PERIOD in the Encyclopedic Dictionary:
a, m. 1. The period of time during which something happens (begins, develops and ends). P. flowering. Incubation stage of the disease. Periodization... - PERIOD in the Encyclopedic Dictionary:
, -a, m. 1. The period of time during which something. occurs (begins, develops and ends). Post-war p.P. heyday. Incubation… - PERIOD
HALF-LIFE of a radionuclide (T 1/2), the period of time during which the number of radioactive nuclei on average decreases ... - PERIOD in the Big Russian Encyclopedic Dictionary:
PERIOD OF OSCILLATIONS, name. the period of time after which the oscillating system returns to its original state. P.k. is the reciprocal of frequency... - PERIOD in the Big Russian Encyclopedic Dictionary:
PERIOD (geol.), large geological interval. time during which the forge was formed. rocks that make up the geol. system. P. are divided into geological. ... - PERIOD in the Big Russian Encyclopedic Dictionary:
PERIOD (music), see Musical form... - PERIOD in the Big Russian Encyclopedic Dictionary:
PERIOD, in poetics (especially in rhetoric), expanded complex sentence with clear intonation and division into columns (example - everything... - PERIOD in the Big Russian Encyclopedic Dictionary:
PERIOD (from the Greek periodos - detour, rotation, defined circle of time), a period of time covering a certain completed process. Society stage. development, society ... - PERIOD in the Complete Accented Paradigm according to Zaliznyak:
peri"od, peri"ode, peri"ode, peri"ode, peri"ode, peri"ode, peri"ode, peri"ode, peri"ode, peri"ode, peri"ode, ... - PERIOD in the Dictionary of Linguistic Terms:
(Greek periodos—detour, circle, rotation). A very common simple or polynomial sentence difficult sentence, characterized in terms of content by significant completeness and... - PERIOD in the Dictionary for solving and composing scanwords:
One third of the hockey... - PERIOD in the Thesaurus of Russian Business Vocabulary:
- PERIOD in the New Dictionary of Foreign Words:
(gr. pertodos bypass, rotation) 1) the period of time during which something happens; 2) stage of social development, social movement; 3) … - PERIOD in the Dictionary of Foreign Expressions:
[ 1. the period of time during which something happens; 2. stage of social development, social movement; 3. astre, period of time, in ... - PERIOD in the Russian Language Thesaurus:
1. ‘a period of time during which any processes or events occur’ Syn: time, time, era, times, century, term, segment, interval; stage... - PERIOD in Abramov's Dictionary of Synonyms:
cm. … - CAMBRIAN in the New Explanatory Dictionary of the Russian Language by Efremova:
adj. 1) Correlative in meaning. with noun: Cambrian associated with it. 2) Characteristic of the Cambrian, characteristic of ... - CAMBRIAN in Lopatin's Dictionary of the Russian Language.
- CAMBRIAN in the Complete Spelling Dictionary of the Russian Language.
- CAMBRIAN in the Spelling Dictionary.
- PERIOD in Ozhegov’s Dictionary of the Russian Language:
period of a function In mathematics: a quantity, when added to the argument of a certain function, the value of the function does not change the period of time, in ... - PERIOD in Dahl's Dictionary:
husband. term or period of time, duration; time from one event to another. History is divided into periods and periods. The primordial period is... - PERIOD in Ushakov’s Explanatory Dictionary of the Russian Language:
period, m. (Greek periodos) (book). 1. A period of time during which something ends. repeating process (scientific). The synodic period of the planet's revolution... - CAMBRIAN in Ephraim's Explanatory Dictionary:
Cambrian adj. 1) Correlative in meaning. with noun: Cambrian associated with it. 2) Characteristic of the Cambrian, characteristic of ... - CAMBRIAN in the New Dictionary of the Russian Language by Efremova:
- CAMBRIAN in the Bolshoi Modern explanatory dictionary Russian language:
adj. 1. ratio with noun Cambrian associated with it 2. Characteristic of the Cambrian, characteristic of ...
Cambrian system (Cambrian) ( from Cambria (Cambria) – Latin name Wales) - the first system of the Paleozoic era, corresponding to the first period of the Paleozoic era geological history. The system was first identified by the English researcher A. Sedgwick in 1835.
The Cambrian period began 542 ± 2 million years ago and lasted ~54 million years. This period began with an astonishing evolutionary explosion, during which representatives of most of the main groups of animals known to the world first appeared on Earth. modern science. The boundary between Precambrian and Cambrian runs along rocks, which suddenly reveal an astonishing variety of animal fossils with mineral skeletons - the result of the "Cambrian explosion" of life forms.
One of greatest mysteries in the history of the development of life on Earth. It took 2.5 billion years for the simplest cells to develop into more complex eukaryotic cells, and another 700 million years for the first multicellular organisms to arise. And then, in just 100 million years, the world became populated by an incredible diversity of multicellular animals. Since then, for more than 500 million years, not a single new type (fundamentally different body structure) of animals has appeared on Earth.
Animals, until they had solid skeletons, were very rarely preserved as fossils. Accordingly, very little information about them has reached us.
But why did so many animals develop skeletons now, and not before, in the Precambrian? It seems that a certain amount of oxygen is required in order for the animal's body to deposit the minerals necessary for the formation of the skeleton. Perhaps the oxygen concentration in the atmosphere became sufficient for this only in the Early Cambrian.
During the Cambrian period, there were huge areas on Earth occupied by the continental shelf, or continental shoals. created here ideal conditions for life: a bottom covered with a layer of soft silt, and warm water. By this time, a lot of oxygen had formed in the atmosphere, although there was less of it than today.
New predators ate the ancient stromatolite reefs, and as they collapsed, they released more and more calcium into the ocean waters, suitable for the formation of skeletons and shells. In addition, the Cambrian climate was moderate, the continents were unchanged. As a result of the increased washout of salts from land, marine animals were able to assimilate large quantities mineral salts.
And this, in turn, opened up wide avenues for them to build a rigid skeleton. It was during the Cambrian period that skeletal organisms appeared for the first time in geological history. The skeletons were secreted mineral - phosphate, calcareous, silicon.
Shells and shells not only served as reliable support for the animals’ bodies, but also protected them from the abundance of predators that appeared around them.
More rigid skeletons allowed the animals to switch to a new way of life: they were able to rise above the bottom silt, and therefore move faster along the seabed. As soon as animals developed articulated limbs, a wide variety of methods of locomotion became available to them, including walking and swimming. The bristly limbs were also suitable for filtering food from sea water, and the articulated mouthparts opened up new opportunities for capturing prey.
The development of hard surfaces led to the emergence of new life forms, such as arthropods and arthropods. Animals needed new ways to protect themselves from new highly organized predators. The means of their defense have improved - and predators have had to develop new hunting methods in order to overcome the resistance of the prey.
During the Cambrian period, sea levels rose and fell repeatedly. At the same time, some populations died out, and their habitats were occupied by other animals, which, in turn, had to adapt to new living conditions. Over time, Cambrian animals mastered more and more specialized feeding methods. Animal world became more diverse, and that's all more types animals could exist side by side, without claiming the food resources of their neighbors. Never again on our planet will there be so many unoccupied ecological niches and such weak competition between species - in other words, such unlimited opportunities for experimentation on the part of nature.
It seems that during the “evolutionary explosion” of the Cambrian period, nature almost deliberately experimented with a huge amount a variety of life forms. True, in the end only very few of them have survived to this day. During the Cambrian, many strange types and “projects” of animal structure arose that have long since disappeared from the face of our planet. There were many groups of animals that were well known to us at that time. In fact, by the end of the Cambrian period, virtually all of the present types of solid-bodied animals had appeared.
So why hasn't evolution produced new types of animals since then? Maybe some changes occurred in their genetic structure and they lost the ability to transform so quickly? Or did the great diversity of species create the strongest interspecific competition that leaves too little room for experimentation? One thing is certain: these days, any freed ecological niche are instantly filled by existing animals that are perfectly adapted to the given habitat.
The Early Cambrian is characterized by foraminifera and primitive shrimp, trilobites and archaeocyaths; there were brachiopods, gastropods, mollusks, sponges, coelenterates, worms, ostracods, echinoderms; microdictyon and tommotia, at the end of the Cambrian period tabulates and graptolites were common, and very highly organized predators - such as cephalopods(like modern octopuses and squids) or primitive armored fish, glassy sponges. There could already be worms and centipedes that came to land.
In general, all types of animals known at present are known from Cambrian deposits, with the exception of bryozoans.
Predators were diligently destroying the ancient Precambrian stromatolite reefs, but new tireless limestone producers had already taken over the work. These were archaeocyaths, primitive sponge-like organisms that quickly spread throughout the world and evolved into many different species. Archaeocyaths, in turn, suddenly declined and became completely extinct in the middle of the Cambrian, but by that time the first corals had appeared in the seas - although they had not yet begun to build reefs.
The end of the Cambrian was marked by a new ice age. Sea levels have dropped sharply. This led to the destruction of many natural areas and, accordingly, the extinction of many animal species.
The first chordate fish had a caudal fin, V-shaped muscle groups and a structure reminiscent of the mouthparts of a jawless fish, with teeth made of dentin and enamel, like those of a vertebrate. Towards the end of the period, the first vertebrates, the so-called pteraspid fish, also appeared.
Among other things, the first chordates appeared in the Cambrian, representatives of the very group whose evolution ultimately led to the emergence of humans on Earth. The first candidate for the ancestors of all chordates can be considered the small fish-like animal Pikaya from the Burgess shale. In appearance, it resembled a lancelet, with a long, hard stripe along the entire body and individual segments that looked like groups of muscles. The flora of the Cambrian period is represented by blue-green and red algae and primitive higher plants. Among the mineral resources of the Cambrian period, deposits of phosphorites are significant.
Cambrian (from Cambria, the Latin name for Wales), the first period of the Paleozoic. Follows the Vendian, precedes the Ordovician period. Start abs. dated 570 ± 20 million years ago, end 490 ± 15 million years ago, duration approx. 80 ± 20 million years. At the beginning of K. p.... ... Biological encyclopedic dictionary
First geol. the period of the Paleozoic era lasting about 70 million years. Its beginning is marked by extensive sea transgression, which apparently reached its maximum in the middle of the Early Cambrian era. On Wednesday. Cambrian occurred in many places... Geological encyclopedia
CAMBRIAN PERIOD - early period Paleozoic era. Multicellular organisms appear in the K. region, the oxygen content is 3 10% of modern ... Dictionary of botanical terms
Cambrian period- Cambrian/Cambrian system The first period of the Paleozoic era in the geological history of the Earth... Dictionary of many expressions
Cambrian period- (geol.) ... Spelling dictionary of the Russian language
Million years Period Era ... Wikipedia
Cambrian- oh, oh.; (from the Latin Cambria the old name of Wales) Cambrian period Cambrian system ... Dictionary of many expressions
Aya, oh. [from lat. Cambria is the old name for Wales] ◊ Cambrian period; Cambrian system. The first period of the Paleozoic era in the geological history of the Earth... encyclopedic Dictionary
- (Cambrian) (from Cambria, Cambria is the Latin name for Wales), the first system of the Paleozoic erathema, corresponding to the first period of the Paleozoic era of geological history. The Cambrian period began 570±20 million years ago, lasting 80 million years. Widely... encyclopedic Dictionary
Geochronological scale Phanerozoic Cenozoic Quaternary Neogene Paleogene Mesozoic Cretaceous Jurassic Triassic Paleozoic Permian Carbon Devonian Silurian Ordovician Cambrian Proterozoic ... Wikipedia
Books
- The organic world on Earth is the creation of extraterrestrial civilizations. From the Cambrian period to the Neolithic, G. N. Kleimenov. In the book, the author claims and proves that organic world was created, starting with multicellular organisms that appeared in the Cambrian period (about 540-560 million years ago), alien...
CAMBRIAN PERIOD
The Cambrian period received its name from the county of Cambria (England), as sediments of the Cambrian period were first described here.
In the Cambrian, on the site of North America and Greenland, there was the continent of Laurentia. The Brazilian continent extended south of Laurentia.
The African continent at that time included Africa, Madagascar and Arabia. To the north of it was located the small Russian continent.
Where China is now, there was the Chinese continent, and to the south of it was the huge Australian continent, covering the territory of modern India and Western Australia. At this time, the Northern Appalachians, the Chingiztau Mountains in Kazakhstan and the Salair-Sayan Range were formed.
Of the Cambrian deposits, the most common are limestones, dolomites, and clayey shales. Shallow lagoon deposits are also common: sandstones and clays with layers of rock salt and gypsum.
In the northern hemisphere, several zones can be distinguished in which the climate was dry and hot.
Thick layers of salts and gypsum were deposited in these places. Australian limestone deposits with desiccation cracks also indicate a hot and dry climate on the Australian mainland during the Cambrian period.
All life in the Cambrian period was closely connected with the aquatic environment.
There was no life on land yet. Of the plants of the Cambrian period, those living in sea water calcareous algae. After they died, accumulations of limestone were formed, known as oncoids. Without a doubt, there were other algae in the Cambrian seas: blue-green, red. But they didn't have solid formations, so their remains have not survived to this day.
Algae, releasing free oxygen, significantly changed the composition of the Cambrian atmosphere.
This created the opportunity for the development of other forms of life, in particular those groups of animals that consume free oxygen. Our knowledge of the animal world of the Cambrian period is very limited.
Cambrian rocks were repeatedly metamorphosed, leading to the disappearance of many prints and fossils. Many Cambrian deposits have not yet been studied. The best studied animals were those that lived in shallow seas near the coast.
The fauna of relative deep water and open ocean almost unknown to us.
Along with numerous representatives single-celled organisms Colonial organisms also lived in the seas of the Cambrian period.
Many fossilized passages made by some worm-like creatures have been preserved. From Cambrian deposits, only individual representatives of the type of mollusks common in our time are known. The shells of bivalves and gastropods are similar to modern freshwater forms. Among cephalopods, large horny organisms are known, the shells of which are divided into chamber-tubes about 8 mm long and 1 mm wide. Inside the chambers there was a thin tube (siphon).
Cambrian period
The Cambrian system (Cambrian) (from Cambria (Cambria) - the Latin name for Wales) is the first system of the Paleozoic era, corresponding to the first period of the Paleozoic era of geological history. The system was first identified by the English researcher A. Sedgwick in 1835.
The Cambrian period began 542 ± 2 million years ago.
years ago and lasted ~54 million years. This period began with an astonishing evolutionary explosion, during which representatives of most of the main groups of animals known to modern science first appeared on Earth. The boundary between Precambrian and Cambrian is marked by rocks that suddenly reveal an astonishing variety of animal fossils with mineral skeletons - the result of the "Cambrian explosion" of life forms.
One of the greatest mysteries in the history of the development of life on Earth. It took 2.5 billion years for the simplest cells to develop into more complex eukaryotic cells, and another 700 million years for the first multicellular organisms to arise. And then, for just 100 million.
years, the world was populated by an incredible diversity of multicellular animals. Since then, for more than 500 million years, not a single new type (fundamentally different body structure) of animals has appeared on Earth.
In the Cambrian, on the site of North America and Greenland, there was the continent of Laurentia. The Brazilian continent extended south of Laurentia. The African continent at that time included Africa, Madagascar and Arabia. To the north of it was located the small Russian continent.
A fairly wide sea basin separated the Russian continent from the Siberian continent, which was located on the site of modern Western Siberia.
Where China is now, there was the Chinese mainland, and to the south of it there was the huge Australian mainland, covering the territory of modern India and Western Australia.
At this time, the Northern Appalachians, the Chingiztau Mountains in Kazakhstan and the Salair-Sayan Range were formed. Of the Cambrian deposits, the most common are limestones, dolomites, and clayey shales. Shallow lagoon deposits are also common: sandstones and clays with layers of rock salt and gypsum.
In the northern hemisphere, several zones can be distinguished in which the climate was dry and hot. Thick layers of salts and gypsum were deposited in these places.
Australian limestone deposits with desiccation cracks also indicate a hot and dry climate on the Australian mainland during the Cambrian period.
The climate of the African continent was apparently warm and humid. IN South Australia, China and Norway had glaciers. When comparing the shores of the Cambrian seas with the shores modern seas we can conclude that most of The earth's surface in the Cambrian period was dry land.
There were many volcanic islands in the shallow seas. Cambrian flora and fauna spread to globe from Cambrian tropical seas.
The flora of the Cambrian period is represented by blue-green and red algae and primitive higher plants.
Among the mineral resources of the Cambrian period, deposits of phosphorites are significant.
The Cambrian period saw rapid development of the animal world.
Cambrian period, or Cambrian (542-485 million years ago)
Some animals that appeared at this time never survived the Cambrian period, such as animals found in the Burges Shale. The Cambrian period also gave rise to all the major groups of animals that exist today, including vertebrates, that is, the group to which we humans belong.
This amazing evolutionary explosion, known to paleontologists as the Cambrian fossil explosion, is difficult to explain.
Nothing like this ever happened again, so why did it happen then? Scientists do not know this, but they have made many assumptions. One of them is that this “explosion” was not at all as amazing as it seems to us now. According to this theory, many species of animals could have existed before the “explosion,” but since they were soft-bodied, there were few traces of their existence.
Many scientists believe this assumption is correct, but they also believe that the “Cambrian explosion” really happened, although it was not as dramatic as it might seem at first glance. It could be caused by changes in oxygen levels in the atmosphere or the topography and structure of the seabed. It is also possible that life has reached some critical point, which entailed chain reaction, during which many new forms of living beings were formed.
The Cambrian period is known as the time when trilobites flourished because of how important role, which these animals played in life on the seabed.
Transparent, gelatinous jellyfish, large and small, swam on the surface of the Cambrian sea. They crowded into the backwaters, waiting out the storms, and again swayed freely on the surface of the sea, merging with sea water, sparkling in the sun. Sometimes the wind and waves washed the jellyfish onto the sand, and they dried up, leaving behind faint imprints. Jellyfish lived in the seas for hundreds of millions of years without changing.
The climate, the composition of the atmosphere, and the salinity of the water changed, but they remained unchanged, because they were ideally adapted to life on the surface of the water.
And at the bottom of the Cambrian seas lived archaeocyaths. Translated into our language, archaeocyath means an ancient bowl. And indeed, with their shape, these animals resemble some kind of fancy glasses, glasses, bowls.
There was a void inside these limestone glasses, and archaeocyaths were attached to the soil with limestone heels. The limestone walls of these bowls had numerous holes through which sea water freely penetrated, washing their soft body, bringing small edible particles to it. Their structure resembles the ancient bowls of modern limestone sponges, but they also had properties that can only be found in corals.
From birth until death, these animals lived in one place, entrenched in the ground, as plants do, without chasing prey, without moving.
It is not for nothing that corals are now often called animal-flowers. But unlike plants, they fed on small plankton and were incapable of photosynthesis, like plants. This means that they were animals after all.
Archaeocyaths did not live long.
Already at the end of the Cambrian they completely disappeared from the bottom of the Cambrian seas and oceans. And they did not live in vain, since it is from these ancient creatures that two large groups animals - sponges and corals. The descendants of the archaeocyaths, more advanced in structure, quickly supplanted their ancestors, stealing food and places suitable for life from them.
Unlike the seas of our time, which are filled with a wide variety of mollusks, there were few of them in the Cambrian seas.
Cephalopods, distant ancestors of modern octopuses, cuttlefish and huge squid, in Cambrian times, were small creatures whose horny shells were divided into a number of small rooms.
In the middle of the rooms ran a thin tube, the so-called siphon, connecting the rooms, allowing the animal to fill them with water or gases.
Brachiopods, or brachiopods, also lived in the Cambrian seas, which scientists named so because they had two fleshy arms, coiled like a clock spring.
Brachiopods were attached to the soil by means of a cartilaginous stalk. The worm-like body of these animals already had a well-developed circulatory system, stomach, greenish glands - liver, pulsating bladder-heart, pigment spots - eyes.
These animals are very interesting for paleontologists, because by studying them, one can understand how and from what complex organs such as eyes, heart, kidneys were formed...
Unlike simple animals, into whose body sea water freely penetrated, carrying with it oxygen and nutrients, the body of brachiopods is already reliably protected by tissue. But, of course, they could not do without sea water completely. Brachiopods, so to speak, took part of the sea into their bodies. Their colorless blood, which carried oxygen throughout the body, is practically no different in its chemical composition from sea water.
The most ancient brachiopods had a chitinous shell, similar to the shell of modern insects.
It is these brachiopods, having lived for hundreds of millions of years, almost unchanged, that have survived to this day.
The ancestors of mollusks and brachiopods were obviously worms. The oldest of the mollusks, which appeared in Precambrian times, differed little from these ancestors in both shape and body structure.
But they already had one significant difference, namely, a turtle. Perhaps the first shells were formed from chitin, because there was still very little lime in the water of the Precambrian seas, therefore, there was nothing for the first mollusks to build a limestone hut from.
But later, when there was more lime in the water, the seas were populated by mollusks with limestone shells. And then real thickets of archaeocyaths and sponges arose at the bottom of the seas...
Cystoids rose above the seabed on long stems. At the tops of the stems there were limestone cups that resembled unopened flower buds.
Tentacle arms were attached to the cups, with which the cystoids pressed seawater with edible particles to their mouths. So, unlike archaeocyaths and sponges, which passively waited until sea waves will bring them food, the cystoids obtained their own food.
They were already crawling along the seabed and sea crayfish. Their elongated body was reliably protected by a hard chitinous shell, and three eyes allowed them to both examine their prey and notice them from afar. dangerous predators- cephalopods.
The crayfish of the Cambrian period already had tentacles that were good at holding captured prey. Some of them swam well, rowing with flat limbs and a wide tail. There were herbivores among the crayfish that ate seaweed, there were also predators. At first they lived only in sea water, but then they also inhabited freshwater pools. It is from them that our crayfish came from.
Cambrian period.
From 570 to 500 million years ago.
The Cambrian period began approximately 570 million years ago, perhaps slightly earlier, and lasted 70 million years. This period began with an astonishing evolutionary explosion, during which representatives of most of the main groups of animals known to modern science first appeared on Earth.
The boundary between Precambrian and Cambrian is marked by rocks that suddenly reveal an astonishing variety of animal fossils with mineral skeletons—the result of the “Cambrian explosion” of life forms.
No one knows exactly what the world map looked like in the Cambrian era, it is only clear that it was very different from today. Across the equator stretches the huge continent of Gondwana, which included parts of modern Africa, South America, Southern Europe, Middle East, India, Australia and Antarctica.
In addition to Gondwana, there were four other smaller continents on the globe, located in what is now Europe, Siberia, China and North America (but together with northwestern Britain, western Norway and parts of Siberia). The North American continent of that time was known as Laurentia.
In that era, the climate on Earth was warmer than today. The tropical coasts of the continents were fringed by giant reefs of stromatolites, which in many ways resembled Coral reefs modern tropical waters.
These reefs gradually decreased in size, as rapidly developing multicellular animals actively ate them. On land in those days there was neither vegetation nor soil layer, so water and wind destroyed it much faster than now.
As a result, it was washed away into the sea a large number of precipitation.
Skeleton Riddle
Animals, until they had formed solid skeletons, were very rarely preserved in the form of fossils.
Accordingly, very little information about them has reached us.
But why did so many animals develop skeletons now, and not before, in the Precambrian?
It seems that a certain amount of oxygen is required in order for the animal's body to deposit the minerals necessary for the formation of the skeleton. Perhaps the oxygen concentration in the atmosphere became sufficient for this only in the Early Cambrian.
The first skeletons were composed primarily of calcium carbonate.
New predators ate the ancient stromatolite reefs, and as they collapsed, they released more and more calcium into the ocean waters, suitable for the formation of skeletons and shells. Shells and shells not only served as reliable support for the animals’ bodies, but also protected them from the abundance of predators that appeared around them.
More rigid skeletons allowed the animals to switch to a new way of life: they were able to rise above the bottom silt, and therefore move faster along the seabed.
As soon as animals developed articulated limbs, a wide variety of methods of locomotion became available to them, including walking and swimming. The bristly limbs were also suitable for filtering food from sea water, and the articulated mouthparts opened up new opportunities for capturing prey.
Fauna of the Burgess Shale.
Eldonia jellyfish (1) sways among the trees glass sponges(vauxium) (2). The strange arthropods Protocaris (3) and Plenocaris (4) swim past Mackensia (5), presumably a species of sea anemone.
It seems tiny compared to the huge predatory Anomalocaris (6), whose powerful mouth may have been capable of crushing the shells of other arthropods. Crustaceans such as burgessia (7) and canadaspis (8) grazed in the mud layer, sucking food particles from it.
Naroya (9) was a primitive soft-bodied trilooite, and the bizarre Vivaxia (10) was a variety ringworm, covered with plates and spines, like canada (1 1).
Even more strange creatures there was Opabinia (12) and Hallucigenia (13), unlike any living animal, and a worm-like odontogryphus (14) with a horseshoe-shaped mouth surrounded by tiny teeth and tentacles.
"Cambrian Explosion"
The Cambrian evolutionary explosion is one of the greatest mysteries in the history of the development of life on Earth.
It took 2.5 billion years for the simplest cells to develop into more complex eukaryotic cells, and another 700 million years for the first multicellular organisms to arise. And then, in just 100 million years, the world became populated by an incredible diversity of multicellular animals. Since then, for more than 500 million years, not a single new type (fundamentally different body structure) of animals has appeared on Earth.
During the Cambrian period, there were huge areas on Earth occupied by the continental shelf, or continental shoals.
Ideal conditions for life have been created here: a bottom covered with a layer of soft silt and warm water. By this time, a lot of oxygen had formed in the atmosphere, although there was less of it than today. The development of hard surfaces led to the emergence of new life forms, such as arthropods and arthropods.
Animals needed new ways to protect themselves from new highly organized predators. Their means of defense have improved, and predators have had to develop new hunting methods to overcome the resistance of the prey.
During the Cambrian period, sea levels rose and fell repeatedly.
At the same time, some populations died out, and their habitats were occupied by other animals, which, in turn, had to adapt to new living conditions. Over time, Cambrian animals mastered more and more specialized feeding methods. The fauna became more diverse, and more and more species of animals could exist side by side, without claiming the food resources of their neighbors.
Never again on our planet will there be so many unoccupied ecological niches and such weak competition between species - in other words, such unlimited opportunities for experimentation on the part of nature.
Burgess Shale
In 1909, the American paleontologist Charles Doolittle Walcott made one of the “discoveries of the century.”
Cambrian period (Cambrian)
In Canadian Rocky Mountains, at an altitude of about 2400 m, he discovered a small lens of shale with what appears to be a number of very strange fossils of soft-bodied animals, many of which are perfectly preserved.
They lived in the early Cambrian in muddy shallow waters adjacent to a large reef. Apparently, part of the muddy shore collapsed and carried these animals with it into a deep bottom depression, capturing along the way some of those who lived in the water column above the reef; they were all quickly buried under a thick layer of silt.
Scientists believe that the Burgues Shale was formed at the dawn of the Cambrian period.
They contain the most various types animals not found in older breeds. Here are arthropods, which crawled in the mud, eating detritus (organic remains), and their relatives - active swimmers and get food by filtering water. Some swimming arthropods, such as the sidney, may have been predators. Other animals lived either on the mud or in its thickness. Among them are numerous varieties of sponges; Brachiopods (brachiopods) settled on the long branches of some of them to filter water.
A strange collection of ancient creatures
Exploring the Burgess shales, Walcott established about 70 genera and 130 species of various animals in them.
He assigned many of them names taken from the local dialects of the North American Indians. Thus, “vivaxia” means “windy” - a very suitable description for this area, and “odaraya” comes from the word “odarai”, which means “cone-shaped”.
The animals themselves turned out to be no less strange than their names. Some of them can still be attributed to some modern group of animals, but most have nothing in common with any other creature known to us, extinct or living today.
Let's say, at goshutzshensh, extremely unusual creature, had a bulbous head and a row of spines running along the back.
Opabinia had five eyes - four of them on stalks - and a long flexible stigma, with which it apparently sucked detritus from the seabed. The tip of the Opabinia stigma forked and was crowned with strange processes. Perhaps she used it as a kind of claw to grab food? Or did the appendages simply push food back into the mouth when it fell out?
Some animals seemed to have traits shared by several modern types.
Odontogus rifus, for example, resembled a flat, segmented worm, but had arthropod-like antennae and many tiny teeth growing around its mouth.
Someone has a caris head and top part the bodies were like those of crustaceans, and the lower part of the body and tail were like those of vertebrates.
Reconstruction of the Late Cambrian shallow seafloor. Numerous trilobites are present here: paradoxid (1), bailiella (2), solenopleura (3), hyolite (4) and agnostus (5).
Sea feathers (6), archaeocyaths (7) and floating graptolites (8) (Dictyonemas) filter water in search of food, and ancient brachiopods (Lingulella) (9) and Billingsella (10) pass water through their shells, using them as a filter.
Great experiment?
It seems that during the “evolutionary explosion” of the Cambrian period, nature almost deliberately experimented with a huge number of different life forms.
True, in the end only very few of them have survived to this day. During the Cambrian, many strange types and “projects” of animal structure arose that have long since disappeared from the face of our planet. There were many groups of animals that were well known to us at that time. In fact, by the end of the Cambrian period, all of the current types of solid-bodied animals had appeared, with the exception of only one.
So why hasn't evolution produced new types of animals since then?
Maybe some changes occurred in their genetic structure and they lost the ability to transform so quickly? Or has the great diversity of species created intense interspecific competition, leaving too little room for experimentation? One thing is certain: nowadays, any vacated ecological niche is instantly filled by already existing animals, perfectly adapted to the given habitat.
Life in the Cambrian seas
The evolutionary explosion of the Early Cambrian produced a wide variety of creatures.
The most important of these are trilobites, arthropods similar in many ways to modern horseshoe crabs. Their bodies were covered with shield-like shells. Most early trilobites lived on the seabed, but some swam in the water above the surface of the bottom and, quite possibly, hunted their relatives who lived in the mud.
Many other organisms also lived in sea water.
They formed food chain(a sequence of living beings that serve each other as food), which was based on millions of floating algae and microscopic animals.
Some of them, such as foraminifera and primitive shrimps, which appeared in the Precambrian, gradually developed hard covers.
Sea waves carried jellyfish and related animals from place to place, and by the end of the Cambrian period, very highly organized predators appeared in the seas - such as cephalopods (like modern octopuses and squids) or primitive armored fish.
Numerous worms swarmed in the bottom silt, feeding on carrion, primitive mollusks similar to modern limpets and sea snails, as well as brachiopods - animals with bivalve shells, something like bivalves on a stalk that extract food from the water around them.
Whole forests of sea feathers swayed above the seabed, carefully filtering the water, and in the quiet waters lived
fragile glassy sponges. By the end of the period, many different spiny derms had appeared, including sea stars and sea urchins.
Two live lancelets
Change on the reefs
Predators were diligently destroying the ancient Pre-Cambrian stromatolite reefs, but new tireless limestone producers had already taken up the work.
These were archaeocyaths, primitive sponge-like organisms, which, however, quickly spread throughout the world and evolved into many different species. Archaeocyaths, in turn, suddenly declined and became completely extinct in the middle of the Cambrian, but by that time the first corals had appeared in the seas - although they had not yet begun to build reefs.
The end of the Cambrian was marked by a new ice age.
Sea levels have dropped sharply. This led to the destruction of many natural areas and, accordingly, the extinction of many animal species.
A Fossil chordate animal. They included a caudal fin with V-shaped muscle groups and a structure resembling the mouth part of a jawless fish, with teeth made of dentin and enamel, like those of vertebrates. Towards the end of the period, the first vertebrates, the so-called pteraspid fish, also appeared.
Fossil chordate
human tail
Among other things, in the Cambrian the first chordates appeared, representatives of the very group whose evolution ultimately led to the emergence of Man on Earth.
All chordates, at some stage of their development, have gill slits and a clearly defined neural tube running along the back, on both sides of which are paired muscle groups. Subsequently, a bony spine or spine is formed around the neural tube, which is why higher chordates are called vertebrates.
The part of such a ridge that extends behind the anus of the animal is called the tail. Chordates also have a tough cartilaginous string (notochord) that runs along the animal's back at some point in its life cycle. The notochord is still present in the embryos of vertebrates, including humans.
Three groups of early chordates are thought to have existed in the Cambrian.
All of them had a fish-like shape, and the dorsal neural tube turned into a long tail, driven by V-shaped muscle groups. Gill slits were located directly behind the head. Similar animals live on Earth today - these are tadpole-like larvae of ascidians and adult lancelets.
The first candidate for the ancestors of all chordates can be considered the small fish-like animal Pikaya from the Burgess shale. In appearance, it resembled a lancelet, with a long, hard stripe along the entire body and individual segments that looked like groups of muscles.
Anatomy of a trilobite
Trilobites great and terrible
Trilobites were the true masters of the Cambrian seas.
They burrowed into the sediment, crawled along the seabed, plowed the dark ocean depths and swam in the upper layers of the seas, permeated sunlight. Many of them ate the remains of dead animals and detritus that accumulated in bottom sediments, but there were also active predators among them. Some trilobites may have even hunted their relatives who lived in sea mud deposits.
The largest of the trilobites had a length of over 70 cm, and the smallest did not reach even a centimeter.
Trilobites looked similar in appearance to modern “king crabs” (horseshoe crabs), their distant relatives. The name “trilobites” itself means “three-membered”: their shell consisted of three sections - a central, or axial, and two flattened lateral sections on both sides.
Most trilobites had a thyroid head, a flexible thorax ( middle part) of articulated segments and a flat tail, often elongated into a long tail spike. Fossil trilobites are found curled up in a ball, like woodlice - perhaps this is how they protected themselves from enemies.
Each segment of the trilobite's body had a pair of limbs.
Those of them that were located near the mouth served as palpating antennae. On the other limbs, feathery gills for breathing, swimming plates or legs for walking, and special processes were attached, with the help of which food was transmitted along the body to the mouth. The shell was often covered with grooves and bulges that broke it into pieces.
Some trilobites have shells riddled with tiny holes, perhaps in places where hairs used to grow, serving as organs of touch or taste.
Types of trilobites
Shards of the past
Like other arthropods, trilobites had a hard outer covering that they periodically had to shed (as when molting) in order to grow.
The covers shed by trilobites are perfectly preserved in fossil form. However, to make shedding easier, their shells had weak lines, or seams. Buried under a layer of sediment, the shells of trilobites, as a rule, split along these lines, so that they are found extremely rarely in their entirety.
Investigating the "trilobite case"
How do we learn about the lifestyle of trilobites? For example, the remains of their mouth parts and front legs allow us to find out something about how they fed.
And yet, did they swallow sediments along with the nutrients they contained, or did they eat detritus directly from the seabed? And how did they move? Did the predatory trilobites chase their prey or lay in wait in ambush?
Answers to some of these questions can be obtained by studying fossilized prints - traces left by trilobites as they moved along the seabed.
Making their way through the thickness of the silt, they left behind them a trail that looked like a “Christmas tree.” And when the trilobites rested, marks resembling hoof marks remained in the rock.
The first eyes on Earth?
Trilobites were the first animals known to us with highly developed vision.
Perhaps their vision helped them notice dangerous predators in time. Like the eyes of modern insects and crustaceans, the eyes of trilobites were complex and consisted of clusters of tiny lenses. These lenses turned out to be strong enough to survive in fossil form.
The sizes and shapes of trilobite eyes are extremely diverse.
There were also completely blind trilobites - perhaps because they lived in the thickness of bottom sediments or on great depths where there is little light. Some trilobites had panoramic eyes that gave a wide view. Others had eyes on the sides of their heads. In still others, they were located at the very top of the head or even stuck out on stalks, so that the animals could probably bury themselves almost entirely in the mud, but at the same time keep a vigilant eye on possible threats or prey.
Active trilobites had bulging eyes at the front of their heads. The fields of vision of both eyes crossed, which allowed the animal to more accurately determine the distance to the object and calculate its speed.
Swimming trilobites acquired wide and flat tail shields.
Such species had light shells and many processes that increased the surface of the animal’s body - this helped it stay afloat. Deep-sea trilobite species used the appendages to lift themselves above the sediment, possibly to extract food particles from seawater.
This fossilized imprint, called a cruciana, was left by a crawling trilobite.
Trilobite extinction
Trilobites reached their peak during the Ordovician period, but by the end of the Paleozoic era, 225 million years ago, they became completely extinct.
Rapidly evolved shellfish and fish learned to deal with them, despite their shells. In addition, they successfully competed with trilobites for food resources.
Chained in "armor"
Some trilobites could roll up in such a way that their strong “armor” completely covered the more vulnerable abdominal cavity.
The boundary between Precambrian and Cambrian is marked by rocks that suddenly reveal an astonishing variety of animal fossils with mineral skeletons - the result of the "Cambrian explosion" of life forms. The supercontinent Gondwana stretches across the equator. Along with it there were four more continents of smaller sizes, corresponding to present-day Europe, Siberia, China and North America. In shallow tropical waters, extensive stromatolite reefs form. Intense erosion occurred on land, and large amounts of sediment were washed into the seas. The oxygen content in the atmosphere gradually increased. Towards the end of the period, glaciation began, leading to a drop in sea level.
Organic world
Cambrian - the time of the emergence and flourishing of trilobites. They are an ancient group of arthropods, closest to crustaceans. All famous representatives The trilobite class were marine animals. At the beginning of this period, organisms with mineral skeletons arose. All types of animals currently known appeared, with the exception of bryozoans.
For a long time, the “explosive” appearance of life in the Cambrian period baffled scientists. But latest discoveries paleontologists have proven that multicellular life did not arise in the Cambrian, but much earlier, and in the Cambrian organisms “learned” to build mineral skeletons, which have a much greater chance of fossilizing and being preserved in rock strata than the soft bodies of animals.
Mostly the Cambrian biota lived in marine basins. There were a large number of trilobites, gastropods, brachiopods, and at the same time there were animals that are difficult to attribute to any known group. In general, even species belonging to known types, they are completely different from modern ones. The reef-building organisms were archaeocyaths, which existed only in the Cambrian, and algae that secreted lime. Apparently, the first terrestrial invertebrates arose in the Cambrian - centipede worms. Also during this period, algae appeared, coral polyps, sponges, cephalopods and arthropods.
Loading...
