The first messengers of the Phanerozoic. Reconstruction
The first era is called the Paleozoic («Ancient Life»). The Paleozoic is divided into several periods. Let’s remember; Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian. These periods of time last for 20—60 million years.
In the Cambrian, organisms learn to build strong skeletons, which can be identified by paleontologists or forensic experts. The star of this period is the trilobite, a pretty rounded arthropod, a kind of prototype of modern cancer.
Trilobite
There are those that, with some stretch, can be ranked among the modern cephalopods – reminiscent of octopuses and squids. Their heyday falls on the Ordovician. The Silurian, lasting “only” 25 million years, is marked by two massive (up to 50% of the genera of marine life) extinctions. One of them, which occurred 443 million years ago, Ordovician-Silurian, was caused by the movement of the Gondwana continent to the South Pole and a sharp drop in ocean level. The already thriving brachiopods (something like our oysters), bivalve molluscs, bryozoans (colonies of small worms) and corals were especially affected. The Devonian period is characterized by terrestrial vertebrates, the famous cross-finned fish, insects, as well as gymnosperms (“naked” seeds are hidden in cones), fern and horsetail plants. Shellfish and fish appear. Trilobites, on the other hand, are rapidly dying out with such an abundance of predators. However, a massive pestilence at the end of the Devonian affects more than half of all marine life. The reason for this may be the fall of a comet.
Labyrinthodont
Quite a long (60 million years) Carboniferous period, or Carboniferous, begins 359 million years ago. It is characterized, as the name implies, by intense coal formation. Gymnosperms develop and thrive: conifers, cordaites (trees that resemble these very conifers), and cicadas (a cross between a palm tree and a fern), baluns and horsetails. Amphibians thrive in warm swamps. Here are the stegocephals, they are labyrintodonts, resembling a crocodile-newt, and ripidists, an even larger 8-meter crocodile. In the seas, sharks frolic, reaching 13 meters. lengths Above our heads soar mega-neuras – dragonflies with a wingspan of up to 65 cm. This heady air itself is characterized by an increased – up to 35%, oxygen content (now 21%).
In the Permian period (the name comes from the naming of the Russian city, in the vicinity of which this stage is highlighted), the continents are united in a different way. Formed, washed by the great ocean of Panthalassa, the global land of Pangea.
Pangea
In the Jurassic period of the next era, it will split into the six continents we know. The geological process is now characterized by a sharp decrease in the area of inland water bodies and the onset of deserts. Sand dunes cover almost the entire territory of present-day Siberia. Carboniferous deposits (coal) are overlain by Triassic variegated sandstone and shell limestone.
The successes of speciation of the Permian are rather modest – only a few species of insects. The period ends with the largest Permian-Triassic extinction in history, 252 million years ago. In less than 60 thousand years, 96% of marine species, 70% of terrestrial vertebrates and 83% of the insect class die. The main hypotheses of the causes of this event are as follows. The first is the fall of an asteroid with a diameter of several tens of kilometers onto our planet. A crater in the Wilkes Land area in Antarctica, a 300 kilometer ring anomaly, seems to confirm this version. The second is the release of greenhouse gas from frozen and for the time being resting at the bottom of methane hydrates. In this case, the oceans boil, riddled with bubbles, like champagne in a bottle freed from a cork. In less than half a century, the water column releases four trillion tons of methane into the atmosphere. The weather is going crazy, harsh, 6 Сº in a year of warming give way to cold snaps and this is not at all to the liking of the inhabitants of the planet. The third is anoxia (suffocation). Water interacts with hydrogen sulfide released into the atmosphere by Siberian traps, flooding vast territories with lava and losing oxygen. Animal remains also emit hydrogen sulfide, which exacerbates the tragedy.
Be that as it may, the cute trilobites, and with them the Paleozoic itself, comes to an end.
The restoration of the biosphere takes five million years. The Triassic, the first period of the Mesozoic era, opens.
Archosaurus, the initial lizard
Of the surviving reptiles, archosaurs stand out. Who are these «initial lizards»? They are classified according to the characteristics of the skull, nasal septum and jaws. The lucky ones become the ancestors of modern birds and crocodiles, as well as the entire family of dinosaurs. Belemnites appear, a kind of squid, ammonites with shells twisted into a spiral, gastropods (gastropods), i.e., snails, as well as bivalve mollusks known to us – oysters.
Bony fishes, they are also ray-finned fishes, are distinguished from armored fish with ganoid scales (rhombic plates that connect in a semblance of an external skeleton).
A classic turtle is being formed.
Ammonite
Synapsids, they are also theromorphs, they are animal-like, namely, their suborder cynodonts of the theriodonts group (animal-toothed lizards), according to Darwin’s theory, become the ancestors of us mammals. This lizard has four very long legs, lays eggs, has wool, judging by the structure of the nasal septum, it warms the inhaled air and, in general, is no longer a cold-blooded reptile.
The Triassic lasts 50 million years and ends 200 million years ago with another global catastrophe. The reasons for the Triassic-Jurassic extinction may be the same that marked the onset of this era. The result is the liberation of ecological niches that dinosaurs immediately occupy.
Dinosaurs, that is, «terrible lizards» differ from the usual reptiles for this time only in size. There is no fundamental difference. But, size does matter. The largest representative of the group of herbivorous sauropods (tetrapods) – seismosaurus, reaches 36 m in length, 20 m in height and weighs 140 tons. Titanosaurus weighs only 50 tons, but is much more widely represented in fossil remains. Theropods, that is, bipedal animals, are usually predators. Their champion is Tyrannosaurus Rex. Height to the end of the thigh is 4.5 meters, length is 13 m, weight is 8 tons. The modern African elephant can boast of a slightly smaller mass.
Titanosaurus. Art object, reconstruction
The Jurassic period (named after the Jura mountains in Switzerland) is characterized by clastic rocks (sharp stones), shales (layered accretion of minerals), igneous rocks (basalt is a loose gray stone with crystalline inclusions), clays and sands. All this is evidence of the disintegration of Pangea into continental blocks, with the accompanying formation of many shallow warm seas. Treelike ferns with branches lying in one plane, forming a semblance of a leaf, and also, similar to palm trees, but less lush 10—18 meter cycads, are spreading. Reef communities (simply reefs) are formed from coral polyps formed in the Triassic.
Archeopteryx appears – an «ancient bird» the size of a crow, clumsily, according to paleontologists, planning from tree to tree. Actually, the scientific community still does not have a generally accepted theory of the origin of birds. It is in the Jurassic that pterosaurs, flying warm-blooded lizards, conquer the air. A well-known representative of this genus, the pterodactyl suborder – pteranodon