For the past
Human beings always have an innate curiosity and awe
For life
There are still many unknowns for human beings to be explored
After the post-disaster reconstruction of the Silurian Period, the time came to the Devonian Period. The Devonian period was a magical era in which the biological world underwent many earth-shaking changes over the course of 60 million years. In the cruel arms race in the animal kingdom, the survival law of "natural selection and survival of the fittest" is truly interpreted. The Devonian period is known as the "age of fish", and the chordates, which were born as early as the Cambrian, finally rose after more than 100 million years of oppression, and since then vertebrates have always occupied the position of biological hegemony. For a time, the ocean has been occupied by a wide variety of fish, among which shield fish also produced the male hegemon of the sea "Dun's fish", under the oppression of strong bite force, various creatures have looked for ways to cope, some animals swim faster and faster, some grow harder thorns, and even some climb up the coast, swim to fresh water, and the emergence of these creatures known as "fish and stone salamander" has also become a major turning point in the history of the earth, and the ancestors of human beings touched the warm land for the first time... The Devonian Period staged a wonderful drama, the fish lying down to taste the guts, ten years of grinding a sword, ammonites to find another way, in the cracks to survive, fish and stone salamanders broke the cauldron, embarked on the road of no return... All the deductions are creating a richer ecological environment behind the earth, let's start from the details and look at the evolution of the earth in the Devonian period.
Map of ecological restoration in the Devonian Period
Fishstone salamander lands
Devonian (symbol D), the fourth period of the Paleozoic Era, dates from 419.2 to 358.9 million years ago, lasting up to 60 million years, marked by the first appearance of the pen stone Uncinatograptus uniformis as the beginning. Before 1830, the academic community believed that the Carboniferous was above the Silurians, but the disunity of the strata gave rise to academic disputes (but the fact that the stratigraphic non-integration challenged this view). Finally, in 1839, british geologists Morrison and Sedgwick proposed that the Stratigraphy could be further divided between the Silurian and Carboniferous, and named it "Devonian" in Devonshire, England. Later, Japanese scholars used the transliteration of Japanese Kanji pronunciation in the translation of "Devonian", which corresponded to the great development of land and fresh water in the Devonian period, so the name "devonian" is also more appropriate and has been used to this day.
Devon, England
From bottom to top, the Devonian system can be divided into three systems: lower Devonian, Middle Devonian and Upper Devonian, including 7 orders, namely Lochkaov, Bragg, Ames, Eiffel, Givingt, Fra and Famen.
Deck of the Devonian International Chronology
The geography of the Early Devonian, with the continents of Lauren and The Baltic continents connected
"European and American continents" were formed
Gradual improvement of the global environment
Before the Devonian Period, the Earth was always in a warm environment, and CO2 was also at a high level. But since the Beginning of the Silurian Plants, plants seem to have come to heaven, and the early fern naked ferns have developed by leaps and bounds. In the Middle-Late Devonians, stone pines, wood thieves, and true ferns were evolved successively, and a large area of vegetation cover gradually changed the earth's environment by photosynthesis. Throughout the Devonian period, plant reproduction reduced CO2 levels to one-tenth of the first dozen, and oxygen concentrations became higher and higher, close to modern levels.
Early Devonian plants were dominated by naked ferns
Devonian forests
The reduction of CO2 content has gradually reduced the temperature of the earth, many climatic cooling events have occurred, and the environment has gradually transitioned from the previous "greenhouse planet" to the "ice chamber planet", and the Devonian is a key period to witness this transition. The early landing of plants and tens of millions of years of environmental modification paved the way for the landing of vertebrates behind.
A forest formed by Devonian stone pine and true fern
Billions of years of pay, the rise of fish
Looking back at the ocean, our human ancestors, the most primitive vertebrates, appeared as early as the Cambrian Period, but they have always been at the bottom of animal society, and hundreds of millions of years of dormancy and silent evolution have written a bitter history of biological evolution.
The Cambrian chordate Kunming fish and Haikou fish are considered to be the earliest vertebrates, and in the Ordovician, these "primitive fish" embarked on the road of escape, and in the process of evolution, they constantly added hard armor to their bodies and became exhausted armorfish. These armor-clad fish have no real mouth, they belong to jawless fish, they can only feed on tiny animals, eat inferior food, but also have to avoid the attack of hornstones and plate-footed horseshoe crabs. This is the condition of our ancestors in the Ordovician and Silurian periods.
The Nailfish of the Silurian Period (painted by Yang Dinghua)
It was not until the end of the Silurian period that the situation changed subtly. A vertebrate classified as the original total jawfish miraculously grew a chin (i.e., a "jaw"), which, while not able to bite freely, was a new leap in the history of biological evolution. The appearance of jawed fish has made fish begin to have the ability to resist. After the food became more nutritious, fish began the first rapid evolution, in the early Devonian period, jawed fish have evolved four major groups including shield fish, cartilaginous fish, spiny fish, teleost fish, teleost fish, including rayfin fish, meat fin fish. The structure of its jaw is also more perfect, it can easily bite the carapace of plate foot crabs and trilobites, and the fish that have been dormant for hundreds of millions of years finally stood up in the Devonian Period, stepped on the feet of the previous hunters, and thus ascended to the position of the supremacy of the sea, laying the hegemony of vertebrates in the biological world.
In the initial total jaw fish recovery chart, jaw differentiation begins to appear
The dream ghost fish found in Qujing, Yunnan Is the earliest bony fish with jaws
Shieldfish prey on plate-footed horseshoe crabs
The huge fish family, which spread rapidly in the ocean radiation and became more and more abundant, became the most common creature in the ocean, so the Devonian period is called the "age of fish". Many fish species have continued to this day, and the shield fish and echinospers in the four major groups have become extinct, and the cartilaginous fish have evolved into today's sharks, rays and so on. The ray-finned fish in the teleost fish are the most common fish today, and the finfish in the bony fish is you in front of the screen (not), they climbed to the shore and evolved into early amphibians, which gave birth to most of the vertebrates. Some of the finfish that did not land are still preserved, such as the lungfish in today's freshwater and the coelacanth in the deep sea. Even jawless fish now have many preserved species, such as lamprey eels, hagfish and so on.
Schematic diagram of fish evolution (source network, illustrated by Bi Xupeng)
Shield fish
Appeared in the Middle Remainian and became extinct at the end of the Devonian period. Shieldfish are the most primitive jawed fish, with a head and thorax covered with bone armor, and the jaw evolved from the arch-like bones that support the gills on both sides of the head. It may be the earliest organism to be fertilized and embryonically developed in vivo.
The carcass turtle was the earliest shield fish
Spiny fish
Appeared in the Late Zhilius and became extinct in the Permian. Spiny fish have even fins, and all but the caudal fins have spines in front of them. The body is covered with dense scales in the shape of a special turtle skin, but is not arranged in a tile-like manner. It is small in size, but hard spines develop in the body.
Spiny fish are characterized by spiny spines
Spiny fish fossils
Cartilaginous fish
It appeared in the late Silurian period and evolved from the spiny fish. Living cartilaginous fish are represented by sharks, and the whole body is composed of cartilage except for the teeth, and the body is scaled or scaleless. In vivo fertilization, oviparous, oviparous or viviparous.
Sharks are representatives of cartilaginous fish, and sharks only have teeth that can be preserved as fossils
Teleost fish
It appeared in the late Silurian period and was divided into spoke-fin fish and meat-finned fish. Most of today's fish are ray-finned fish, characterized by radial fins; flesh-finned fish today have only lungfish and coelacanths, characterized by muscular flesh fins, and lungfish still retain the characteristics of four legs rowing on the bottom of the water.
Modern fish are mostly ray-finned fish
Coelacanths are meat-finned fish that flee to the deep sea
Lungfish still move on their flesh fins in modern freshwater
Undersea Crusher "Dunn's Fish"
The evolution of marine life is a long and surprising process, like a "dark forest" full of hunters and prey, and hunters always have the potential to become prey in a million years. Although the plate-footed horseshoe crab, which has suppressed the fish for a long time, has become a prisoner of the order, but the evolution and competition are not over, and there seems to be a greater danger lurking inside the fish.
Shieldfish prey on beetlefish
The evolution of fish has long diverged, teammates who once worked together against foreign enemies soon became less simple, and the four major groups of fish silently engaged in their own arms race, sharper teeth, faster speed, stronger scales, sharper vision... The Great War is on the verge of breaking out. Finally, in the late Devonian, a terrifying class of fish called "Dun's fish" appeared in the shield fish, and in front of the fish with an average body length of not more than a meter, the Dunn's fish with a body length of up to 8.79 meters looked like a behemoth, wrapped in heavy armor and a sharp bone plate in the mouth and a strong jaw, like an undersea chariot. According to calculations, the bite force of Dunn's fish can exceed 6000 N (that is, 612 kg), although it is far less than the bite force of modern crocodiles and sharks, but at that time, the carp had just appeared in the Devonian Period, which was not long after the jaws of fish, this strong bite force was already top-notch, and could easily crush the shell of any armor fish and ammonite.
The overlord of the sea, the Dunn's Fish
The terrifying skull of the Dunn's fish
Dunn's fish bite model
Full body recovery of Dunn's fish
Dunn's fish also has weaknesses, these fish do not have the function of chewing, so they can only send a brain to the mouth, and then spit out the bones after digestion, but if you swallow the echinococcal fish, which is full of hard fish bones, it is likely to delay the blockage and lead to death.
In addition, the short-breasted fish with thorns that also belong to the shield skin fish have also appeared in the fish called bully fish and the fear fish, but compared with the Small Size and Small Mouth of the Dunn's Fish, it does not have too strong competitiveness, and may also become the "Bully Fish Dumpling" in the mouth of the Dunn's Fish.
Comparison of the length of the Dunn's fish with humans
The bully fish is also a type of shield fish
Although the Dunn's fish ascended to the supremacy of the sea, it was short-lived. The "Shield Fish Dynasty", which only began to be established in the late Devonian, fell with the mass extinction of organisms at the end of the Devonian period, and a generation of marine overlords disappeared from the earth. However, the cartilaginous fish that also developed a strong jaw seemed to have reached a delicate balance in the previous competition, and they were the ancestors of sharks, who repeatedly took over the position of ocean overlord after the shield fish withdrew from the stage.
The pectoral ridge shark of the Devonian period is also representative of the organism, characterized by a bulge at the top
The salamander "forced up Liangshan" and was forced to conquer the land
In the Late Devonian, the evolution of life reached a climax, and different creatures frantically searched for a way to survive. When the Dunn's fish came out, other creatures seemed to have been forced to the end of the road, but the finfish, which belonged to the teleost fish, chose another path.
Meat-finned fish that dominate freshwater
The Titalik is a transitional species from true palm finfish to quadrupeds
The muscular fins were not evolutionary successes, and the thick fins and spear-shaped tails did not swing quickly in the water, making them prey on shallows on the seabed. The slower speed and delicious meat made them fat in the mouths of shield fish, and the fin fish became prey to be slaughtered. But prey does not always want to be prey, and the body structure of the finfish is not suitable for competition in the ocean, but it is unexpectedly suitable for the freshwater environment of the land. At that time, due to the transformation of the surface by The Silurian landing plants, freshwater waters such as rivers and lakes were formed, and the arthropods of the Silurian landings also multiplied on land, but their size was only the size of modern insects, and some meat fin fish chose to come to freshwater and feed on insects and plants. Miraculously, the fins of the finfish are convenient for them to move between puddles, and they can also leave the dry puddles in time when the dry season comes, so these finfish begin to make their home in freshwater waters, unveiling the curtain on the landing of animals.
Comparison chart of finned fish
If you want to land, you also need an important condition, that is, breathing! Skin respiration is too inefficient, while finfish develop early lungs and breathe oxygen freely. Miraculously, bony fish develop mature lungs in the embryonic stage, and the fin fish use their lungs to go to land; the lung of the rayfin fish degenerates into the water and becomes the current swim bladder. Thus, on a long evolutionary road, these meat fin fish that chose to leave their homeland gradually evolved into true palm fin fish, with developed meat fins that can be moved. Later, the front and back fins of these true palm fins became more developed, and began to differentiate into quadrupeds and become quadrupeds that could live amphibians.
The late Devonian tetrapod landings marked a new beginning
The most representative tetrapods are the fishstone salamander, which has four legs with seven toes, broad ribs, large shoulders, and a neck that can be twisted, although the structure of the hind limbs indicates that they are not suitable for walking on land, but at least it can prove that they surfaced and walked towards land, representing the beginning of the vertebrates out of the water. Therefore, the ancestors of human beings did not go to land voluntarily, but were forced by life and then forced to conquer the land.
The salamander began to emerge from the water
Fishstone salamander in the BBC documentary
It is also worth mentioning that the axorupter found in Greenland has a similar structure, with eight toes on the forelimbs, a large tail indicating that they are also predators visiting the land, and their ecological habits are similar to those of modern lungfish.
Acacia reconstruction diagram
Fishstone salamander (top) versus axoruptacea (bottom) bones
Evolution of the palms and toes
(Acanthostega is a salamander, Ichthyostega is a salamander, Tulerpeton is a salamander)
Ammonites and grubs, a new route for cephalopods
In the Devonian oceans, another magical creature was secretly born, whose predecessor was the former ocean overlord stone. Due to the long shell that is inconvenient to turn, the horn stone loses its hegemonic position and gradually withdraws from the historical stage, but some of the pole stone horn stones, if they have found a new way of survival with divine help, they choose to turn the long shell and roll it up, which is the later ammonite.
Ordovician domination of the main house corner stone
Cephalopods diverged in the Devonians
The order Lithomatidae differentiates into ammonite suborders and suborder lycopenes
(Source: Climbing Well Frog)
The ammonite that coiled up was more convenient to move, and even free to float, which was well adapted to the varied living environment at that time. Although the hard shell of ammonites cannot resist the large mouth of the blood basin of The Dunn's fish, at least they occupy a place in the ecological niche.
Devonian-like archaic ammonites
Devonian prismatic ammonites
A variety of strange cephalopods have evolved, including ammonites and grubs
One might ask why ammonites, which appeared as early as the Cambrian, had already rolled themselves up. In fact, the inner volume of ammonite is much more complicated than that of the nautilus, the ammonite will plate more and more circles, and the comparison can be found that the biggest difference between ammonite and nautilus is that there is a separate fetal shell in the center of the ammonite spiral, and the surface ammonite and the nautilus have no "plagiarism phenomenon" in the evolutionary history. Of course, in the sutures, partitions, etc., there is a big difference between the two.
Ammonite fossil profile (non-Devonian)
Modern nautilus shell profile
Another group of cephalopods who went out with ammonites chose another path, and they belonged to the subclass of cockroaches, including squid and octopus. They abandon the shell, some choose to wrap the shell in the body, and some simply abandon the shell, all in order to run faster and hide deeper. These grubs, who dared to give up, managed to survive to the end, and even in modern times still occupy a powerful position on the seabed, such as the mysterious king squid. They learn more magical functions in the process of evolution, such as color change, inkjet, and so on. The cockroaches and nautilus survive to this day, and the ammonites that are cognate with them completely disappeared in the last mass extinction on Earth.
Modern soot maggot, nicknamed "Dumbo"
The devastating blow to the oceans, the second mass extinction
Devonian creatures are magical, and the ocean and land are a vibrant scene: bright reef-building organisms such as bed corals, foraminifera, and four-shot corals cover the seabed; stone swallows, sponges, trilobites, etc. all lie quietly on the seabed; ammonites and a variety of fish travel through the ocean. Everything was renewed, as if there was a bright future, and the carnival of evolution pushed the fish to the pinnacle of living things and even began to take steps towards land. However, behind the beauty is a crisis, and a catastrophe is quietly coming.
The Devonian mass extinction, also known as the "F-F-F turn event", was a major extinction event that caused a devastating blow to marine life. The cause of this mass extinction has been proposed by scholars, but these multiple possibilities have actually occurred at the same time.
First of all, plants build a good ecological environment for animals, but the transformation of plants is endless, the forest is unrestrained expansion, the continent is disintegrated and collapsed so that a large amount of phosphorus flows into the water source, a large amount of released oxygen is combined with lightning and a large amount of nitrogen fertilizer is stored into the water source, the fertilizer water rich in organic nutrients is integrated into the ocean to promote the outbreak of algae, a large number of algae dye the ocean green and red, resulting in the death of a large number of marine organisms, the decomposition of biological remains has aggravated the deterioration of the marine environment, and hypoxia and putrefaction have become the norm of the ocean. This is also an important reason why finfish climb out of the ocean. However, the disaster is not only that, the large reduction of CO2 weakens the greenhouse effect, the earth ushered in a major ice age, the polar glaciers expanded rapidly, making most of the sea cold, corals and other reef-building organisms have fallen, and then the animals that rely on corals for their livelihoods are difficult to support. At this time, the Deng's fish, which had just ascended to the hegemonic position not long ago, had only endless despair in the face of a life of lack of clothing and fasting, and a generation of overlords was forced to perish under the pressure of hunger and cold.
Algae outbreaks cause the oceans to be deprived of oxygen
Fish and ammonites died in large numbers during the F-F incident
However, the extinction catastrophe of the Devonian period was not limited to this, and a fire meteor event that destroyed the world and destroyed the earth caused another major blow to the ecological environment at this time. During the Dharma Period, the first large-scale visit to Earth by extraterrestrial objects since the Cambrian explosion was ushered in.
Some scholars believe that the Siljan pit in Switzerland is a product of this shock event (McGhee, 1996)
During the same period, there were impact craters in many places
Eventually, the mass extinction came to an end after the Meteor Event, in which 82 percent of the creatures were killed, with shieldfish, head turtles, most trilobites, and most of the pencilstones disappearing during the event, and marine life being severely damaged. Fortunately, quadrupeds and arthropods that have adapted to land life have been less affected and survived, so there is a longer story behind.
A generation of overlords, the Dunn's fish, became extinct at the end of the Devonian period
Quadrupeds that came to land were lucky enough to survive the mass extinction
The wheel of history continues, and biological evolution is even further ahead. After the Devonian Period, the emergence of amphibians seems to give us a bright future, but in the next Carboniferous Period, what kind of dangerous environment will they encounter in the face of insects that are longer than meters?
Wait for the next issue, the Carboniferous: amphibians, giant insects, reptiles – a great duel in the forest?
Resources:
[1] Wikipedia
[2] Devonian: March to land – naturalist
[3] Cthulhu 5: Who taught Ru shirtless, the climbing well frog
[4] Meatfin Fish: Target Land - OniGu said
[5] McGhee GR Jr. 1996. The Late Devonian Mass Extinction. New York: Columbia University Press.
[XI Wenkun, MA Xueping, XU Honghe, et al. Comprehensive Stratigraphy and time frame of Devonian in China[J]. SCIENCE CHINA (EARTH SCIENCES), 2019, 049(001): 115-138.
Editor: Yang Xiangtong
Editor: Wang Wanyu
Proofreader: Liu Qijun Zhou Xingxing