Triassic
| It was | Period | Millions of years |
|---|---|---|
| Mesozoica | Cretaceous | 145.0 |
| Jurassic | 201,3 ± 0.2 | |
| Triassic | 251.0 ± 0.4 |
The Triassic is a division of the geological time scale that belongs to the Mesozoic Era; within this, the Triassic occupies the first place preceding the Jurassic. It began 251 million years ago and ended 201 million years ago. It owes its name to the three layers of rock (tri means "three") found by the German geologist Friedrich von Alberti in his studies in Germany and north-western Europe in 1834.
As with most geologic periods, the exact start and end dates are imprecise by a few hundred thousand years. In the case of this period, both the beginning and the end are marked by major extinction events: the Permian-Triassic mass extinction and the Triassic-Jurassic extinction.
The first mammals, which evolved from mammalian reptiles, made their appearance in this period.
Continental drift brought the continents closer together; together with the great marine regression of the Triassic, they were the two causes of the formation of the supercontinent Pangea. At the beginning of the Jurassic the emerged lands separated again. Due to this regression, the continental shelves were above sea level, which led, in turn, to a decrease in the deposition of carbonate sediments, which require relatively shallow depths.
It is in the sediments of this period where the fossils of the first dinosaurs appear, represented by small bipedal, carnivorous forms. However, by the end of the period they had already diversified on a large scale and had become the dominant vertebrates on the entire planet, driving to extinction more primitive groups, such as archosaurs, and mammalian reptiles with few exceptions.
Subdivisions
The International Commission on Stratigraphy recognizes three epochs/series and seven ages/stages of the Triassic, arranged in order from most recent to oldest as follows:
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| It was Eradication | Period System | Época Series | Age Flat | Relevant events | Home, in millions of years | |
|---|---|---|---|---|---|---|
| Mesozoic | ||||||
| Cretaceous | 145.0 | |||||
| Jurassic | 201,3±0.2 | |||||
| Triassic | Superior / Afternoon | Rhaetiense | Rainbows dominate the earth as dinosaurs, in the oceans as ictiosaurus and notosaurus, and in the sky as pterosaurs. Cynodontics become smaller and more like a mammal. The first mammals and the Crocodilia order appear. Plants of the group Dicroidium They were common ground. Many great aquatic amphibians dread them. Extremely common ceratic ammonoids. Modern corals and bone fish (teleos), as well as many of the modern insect nails appear. | ~208,5 | ||
| Noriense | ~227 | |||||
| Carniense |  ~237 | |||||
| Media | Ladiniense | ~242 | ||||
| Anisiense | 247,2 | |||||
| Inferior / Early | Olenekiense | 251,2 | ||||
| Induense | 251,902±024 | |||||
Stratigraphy
The Triassic was named in 1834 by Friedrich Von Alberti due to the three more general sections that make up the sedimentary deposits (from the Latin trias meaning "triad") that usually appear together, with diachronic boundaries and as "packages" solidary, very widely spread throughout Western Europe, under the recognition of the tectofacies called "Germanic", or Second "Red Facies"; extended from Germany and Northern Europe, to the south of the Iberian Peninsula, called the "Trias".
The first basal stretch is made up of sandstones and red conglomerates (Buntsandstein), such as the Lower Trias; a second, intermediate, of carbonate formations typical of shallow marine environments, lagoon type (Muschelkalk), such as the Middle Trias; and a third, of red clays variegated with evaporites (Keuper), from very arid ancient environments, such as Trías Superior, whose materials present a high plasticity (diapirism or halocinosis).
It is also possible to differentiate this Germanic Trias from the Alpine tectofacies Trias, the latter mainly made up of carbonate shifting mantles, for example, the Triassic-age marbles of the Alpujárride Complex of the Penibética mountain range.
The lagerstätte of Monte San Giorgio, now in Lake Lugano, a region of northern Italy and Switzerland, was in Triassic times a lagoon between reefs with an anoxic bottom, so there was no turbulence or problems with fossilization, a situation that can be compared to the better known Solnhofen lagerstätte.
Paleogeography
During the Triassic, nearly all the land on Earth was concentrated on a single supercontinent centered roughly on the equator, called Pangea ("all the earth"). This continent was shaped like a "C" and to the east, in the hollow of the "C" was the Tethys Ocean and surrounding it all was the Panthalassa Ocean (the "universal ocean"). All deep ocean sediments deposited during the Triassic have disappeared through subduction of oceanic plates, so very little is known of the open ocean during the Triassic.
The supercontinent Pangea began its dislocation during this period, especially in the Late Triassic, but had not yet broken apart. Laurasia included North America, Europe, and much of present-day Asia. Gondwana included Africa, Arabia, India, Australia, Antarctica, and South America. Pangea was moving very slowly northward in this period, and in the process the supercontinent began to show the first signs of breaking up, with rifts appearing in eastern North America, central and western Europe, and in northwestern Africa. The first sediments out of the sea, in the rift that marked the initial break of Pangea and that separated New Jersey from Morocco, are from the Late Triassic; in the United States, these coarse sediments comprise the Newark group.
Sea level rose slightly during the Lower Triassic; however, the volume of emerged areas was still very high. The Tethys Ocean, which formed a wide gulf, became a marine invasion route. Although the dominant terrestrial plants in the Triassic differed from the Permian, the distribution patterns over Pangea remained (southern Gondwana flora, Siberian flora, and Laurussian flora of drier and warmer conditions at equatorial latitudes).
Climate
The Triassic climate was generally hot and dry, giving rise to the formation of deserts and evaporites. Pangea's large size limited the moderating effect of the ocean; its continental climate was highly seasonal, with very hot summers and very cold winters. It probably had strong monsoons in Ecuador. There is no evidence of glaciation near or at either pole; in fact, the polar regions were apparently humid and temperate, a suitable climate for reptile-like creatures.
Vegetation
Land plants did not experience a major extinction at the end of the Paleozoic Era. The transition from Late Paleozoic to Mesozoic types began before the start of the Mesozoic Era. Thus, conditions were very similar to the Permian. The plants that flourished in Laurasia were adapted to its hot, dry climate: Cycads. Among the arboreal vegetation there were some conifers and ginkgos. Ferns predominated in the humid areas, along with cycads with a morphology similar to palm trees and some predecessors of today's pines. Gondwana, much wetter, was populated by forests of gigantic ferns and bulky conifers.
There is evidence that beetles were involved in the pollination of some gymnosperms, but otherwise there were few of these plants that tried to attract insects, even the cones of cycads seem designed to repel them. More than half of the known species of insects were equipped to pierce, nibble, and suck on plant bodies.
Triassic forests
An example of a Triassic forest is provided by the Paramillos Formation (Paramillos de Uspallata, Mendoza, Argentina), in which a middle Triassic "petrified forest" is located, with several localities totaling more than 120 fossil trunks, in position of life. It represents a subtropical evergreen forest with a dry season, composed mainly of Corystospermaceae and Araucariaceae. The first locality was discovered by Charles Darwin in March 1835 on his round-the-world voyage aboard HMS Beagle. A monument commemorates the passage of the eminent English naturalist through that place. The area of the so-called "Darwin Forest" contains the largest number of petrified trunks in the Argentine Republic; as well as a great variety of plant, invertebrate and vertebrate fossils.
Paleozoology
Three categories of organisms can be distinguished in the Triassic record: survivors of the Permian-Triassic extinction, new groups that briefly flourished, and new groups that went on to dominate the Mesozoic world.
Terrestrial paleozoology
Triassic fossil records have been found in various regions: in the Karroo Basin of South Africa, in Russia near the Ural Mountains, in Ischigualasto, San Juan, Argentina, in the Petrified Forest of Arizona, etc. All these records tell the same story.
Reptiles dominated the land surface in this period. However, most genera of Permian mammalian reptiles suddenly disappeared. A few genera of predators and the large herbivore Lystrosaurus, which is famous for its fossil presence in many of the widely scattered fragments of Gondwana, remained by the early Triassic. Mammalian reptiles rediversified during the Triassic, playing an important ecological role and leaving an important legacy, the true mammals, which evolved from them at the end of the Triassic. Among the herbivorous species were the dicynodonts, similar to the current hippos; rhynchosaurs, similar to modern pigs; and the cynodonts, similar to the current weasels. All of them disappeared from the face of the earth in an unknown and sudden way: It was the first great mass extinction of terrestrial fauna on our planet. The thecodonts that took over from them disappeared in the second great extinction, which occurred at the end of the Triassic. Only turtles, crocodiles, dinosaurs and some small mammals survived. The first mammals were small and in the minority, throughout the Mesozoic Era, and no species reached significant dimensions.
Lystrosaurus (Dicynodontia)
Cynognathus (Cynodontics)
Ornithosuchus (Archosauromorpha)
Herrerasaurus (Dinosauria)
Plateosaurus (Prosauropoda)
Most dinosaurs appeared in the late Triassic. Among them stood out theropods and prosauropods. In the absence of competition and with empty ecological niches, the first dinosaurs quickly colonized the land. Noteworthy are Procompsognathus and Plateosaurus.
Aerial Palaeozoology
In the Late Triassic, several small reptiles developed membranes over their limbs, possibly allowing them to glide. Some genera had these wings on the front legs and others on the hind legs. The most abundant were the pterosaurs, an order of reptiles other than dinosaurs, warm-blooded, with a large head, small body, and long, narrow wings ending in four tiny claws.
Sharovipteryx (Prolacertiforms)
Eudimorphodon (Pterosauria)
Unlike their predecessors, pterosaurs were already capable, at the end of the Triassic, of making flights of a certain duration, covering distances unprecedented up to now. Fossil pterosaurs are very common and hundreds of specimens have been found, belonging to eight different genera. Eudimorphodon was possibly the first of them all.
Aquatic paleozoology
The most common groups of the Lower Triassic are molluscs. The ammonoids experienced a spectacular recovery after their near extinction in the Permian (only two genera survived). In the Triassic, the ammonoids exceeded one hundred genera. The other oceanic groups were slower to recover, but by the Late Triassic, the seas already had some diversity. Of the group of reptiles, the nothosaurus (sharp teeth, 4 meters in length, small and elongated head and duck-like fins), the placodont (sharp teeth like saws), and the ichthyosaur (up to 15 meters in length and dolphin-like). These species adapted to the aquatic environment fed on fish and mollusks. Nothosaurs, from the Lower Triassic, were close to the placodonts and seem to have been the first reptiles to invade the oceanic realm. They were hydrodynamic with a long neck and four paddle-shaped limbs. Neither placodonts nor notosaurs survived the Triassic period.
Bivalves and gastropods were less affected by the Permian extinction, and are frequently found in Lower Triassic rocks, although their diversity is somewhat limited (endobenthic and epibenthic).
Henodus (Placodontia)
Askeptosaurus (Thalattosauria)
Nothosaurus (Nothosauria)
Lariosaurus (Nothosauria)
Cymbospondylus (Ichthyosauria)
Californosaurus (Ichthyosauria)
Hexacorallia corals appear in the Middle Triassic. The first reefs were small (less than 3 meters) and built by few types of organisms. At the end of the Triassic, the reefs were larger, and some have been built by more than 20 different species. The first bioconstructions grew in relatively deep waters, different from current ones, not associated with symbiotic algae. Perhaps it was not until the end of the Triassic or early Jurassic when they began to form large reefs and this symbiotic relationship was established. The conodonts were still important in the Triassic, to disappear at the end of this period.
Mass extinctions
At the end of the Triassic the mass extinction of the Triassic-Jurassic occurred. Conodonts and placodont reptiles become extinct. 20% of marine animals disappeared, although all these groups recovered in the Jurassic. Land victims included most genera of mammalian reptiles and large amphibians. The primary beneficiaries of extinction on land were the dinosaurs, which expanded rapidly during the Jurassic and dominated terrestrial habitats throughout the remainder of the Mesozoic Era. The only marine reptiles that survived were ichthyosaurs and plesiosaurs.
Evidence suggests that there were two Triassic extinction pulses, one before and one at the end of the period. The timing of these extinctions in the seas is unclear, and the causes of the Triassic extinctions remain unknown. An analysis in northwestern Arizona in 2002 on the Carnian-Norian boundary showed no abrupt changes in the paleoenvironment, so the climatological possibility was not supported. At this time, conifers and other groups of gymnosperms replaced the seed plant floras that had predominated in lowland Gondwanan habitats in the Triassic.
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