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Triassic: the story on HearLore | HearLore
Triassic
The Earth was a scorched and silent place when the Triassic Period began 251.902 million years ago, emerging from the ashes of the Permian-Triassic extinction event that had wiped out approximately 90 percent of all species on the planet. This was not merely a geological transition but a planetary reset button, where the biosphere was reduced to a handful of hardy survivors struggling to repopulate a devastated world. The Early Triassic was the hottest portion of the entire Phanerozoic Eon, a time of extreme thermal instability driven by the discharge of titanic volumes of greenhouse gases from the Siberian Traps, a massive volcanic province that continued to erupt into the Middle Triassic. In this inferno, the fossil record reveals a remarkable uniformity among surviving life forms, with many families and genera exhibiting a cosmopolitan distribution that suggests a global ecosystem stripped of its complexity. The recovery was agonizingly slow, taking 30 million years for diverse communities with complex food-web structures to reestablish themselves, leaving the Early Triassic as a period of biological austerity where the few survivors faced a world that had lost its balance.
The Age of Archosaurs
While the world burned, a new class of reptiles known as archosaurs began to dominate the terrestrial landscape, marking a shift in power that would define the era. True archosaurs appeared in the early Triassic, splitting into two branches: Avemetatarsalia, the ancestors to birds, and Pseudosuchia, the ancestors to modern crocodilians. During the Triassic, pseudosuchians were far more ecologically dominant than their dinosaurian cousins, occupying the large-predator niche that would later be filled by theropods. These creatures included giant quadrupedal hunters, sleek bipedal omnivores, and lumbering beasts with deep sails on their backs, collectively known as rauisuchians. They were the keystone predators of most Triassic terrestrial ecosystems, with over 25 species identified, including the massive Smok, whose classification as a primitive dinosaur or pseudosuchian remains uncertain. Meanwhile, the first dinosaurs evolved in the Carnian period, but they were mostly small predators like Coelophysis, which was only about 3 meters long and remained a minor component of their ecosystems. The true dominance of dinosaurs would not arrive until the succeeding Jurassic Period, leaving the Triassic as the age of the crocodile-line archosaurs.
The Great Coal Gap
The absence of coal deposits from the start of the Triassic Period, known as the Early Triassic coal gap, stands as one of the most striking anomalies in the geological record, signaling a complete collapse of the swamp ecosystems that had generated coal during the Permian. This hiatus of several million years in coal formation was likely caused by a combination of factors, including sharp drops in sea level, acid rain from the Siberian Traps eruptions, and a climate shift to a greenhouse state that was too hot and dry for peat accumulation. In the wake of this environmental collapse, lycophytes, particularly those of the order Isoetales, rose to prominence due to the environmental instability, with the genus Pleuromeia growing in columnar-like fashion and sometimes reaching heights of 10 meters. As the Middle Triassic arrived and environmental conditions stabilized, the relevance of these lycophytes declined, and the extinct seed plant group Bennettitales first became a prominent element in global floras. The tree Dicroidium, an extinct seed fern belonging to the order Corystospermales, became a dominant element in forest habitats across the Southern Hemisphere landmasses of Gondwana, while the Ginkgoales underwent considerable diversification, setting the stage for the conifer-dominated forests of the Mesozoic.
The Triassic Period began 251.902 million years ago and ended 201.4 million years ago. This span covers 50.5 million years, making it the first and shortest geologic period of the Mesozoic Era.
What caused the extreme heat during the Early Triassic?
Extreme thermal instability during the Early Triassic was driven by the discharge of titanic volumes of greenhouse gases from the Siberian Traps. This massive volcanic province continued to erupt into the Middle Triassic, creating the hottest portion of the entire Phanerozoic Eon.
Which animals dominated the terrestrial landscape during the Triassic Period?
Archosaurs dominated the terrestrial landscape during the Triassic Period, with pseudosuchians occupying the large-predator niche. These creatures included giant quadrupedal hunters and lumbering beasts known as rauisuchians, which were far more ecologically dominant than early dinosaurs.
What was the Early Triassic coal gap and why did it occur?
The Early Triassic coal gap refers to the absence of coal deposits from the start of the Triassic Period due to a complete collapse of swamp ecosystems. This hiatus was likely caused by sharp drops in sea level, acid rain from the Siberian Traps eruptions, and a greenhouse climate that was too hot and dry for peat accumulation.
How did the Triassic Period end and what triggered the extinction event?
The Triassic Period ended with a mass extinction triggered by huge volcanic eruptions that formed the Central Atlantic Magmatic Province. This magmatism occurred as the supercontinent Pangaea began to break apart about 202 to 191 million years ago, injecting carbon and sulphur into the atmosphere to cause climate warming and ocean acidification.
The vast supercontinent of Pangaea, which dominated the globe during the Triassic, created a climate of extremes that was largely hot and dry, with deserts spanning much of the interior and no evidence of glaciation at or near either pole. The strong contrast between the Pangea supercontinent and the global ocean triggered intense cross-equatorial monsoons, sometimes referred to as the Pangean megamonsoons, which brought dramatic shifts in weather patterns across the landmass. Despite the general aridity, evidence exists that the period was punctuated by several episodes of increased rainfall, most notably the Carnian Pluvial Event, which was the best-studied of such humid climate episodes and probably the most intense and widespread. This event, triggered by the eruption of the Wrangellia Large Igneous Province around 234 million years ago, caused abrupt global warming and resulted in an episode of widespread global humidity that lasted from 234 to 227 million years ago. The climate shifted and became more humid as Pangaea began to drift apart, with the opening of the Neo-Tethys creating passive margins along the Arabian and Indian margins, and the rifting in the Neo-Tethys extending westwards between the Pontides and Taurides terranes of Turkey during the Late Triassic.
The Rise of the Mammals
In the shadow of the giant reptiles, a small but significant group of synapsids known as cynodonts began to evolve traits that would eventually lead to the first mammals. During the Carnian period, some advanced cynodonts gave rise to the first mammals, known as mammaliamorphs, which were specialized subgroups of cynodonts that survived the extinction event to radiate during the Jurassic. The Triassic Takeover, where archosaurs displaced therapsids as the largest and most ecologically prolific terrestrial amniotes, may have forced the surviving therapsids and their mammaliaform successors to live as small, mainly nocturnal insectivores. This nocturnal life may have forced the mammaliaforms to develop fur and a higher metabolic rate, setting the evolutionary trajectory for the class that would eventually dominate the Cenozoic Era. While the large herbivorous therapsids, such as the kannemeyeriid dicynodonts and the traversodont cynodonts, were much reduced in the northern half of Pangaea, the small cynodonts persisted, their survival ensuring that the lineage leading to humans would endure the mass extinctions that followed.
The Oceanic Recovery
The oceans of the Triassic were a world of recovery and diversification, where new modern types of corals appeared in the Early Triassic, forming small patches of reefs of modest extent compared to the great reef systems of the Devonian or modern times. In the wake of the Permian-Triassic mass extinction, the fish fauna was remarkably uniform, with many families and genera exhibiting a cosmopolitan distribution, but ray-finned fishes went through a remarkable diversification in the beginning of the Triassic, leading to peak diversity during the Middle Triassic. The first stem-group teleosts appeared during the Triassic, and teleosts are by far the most diverse group of fish today, while predatory actinopterygians such as saurichthyids and birgeriids, some of which grew over 5 meters in length, appeared in the Early Triassic and became widespread and successful during the period. Marine reptiles also flourished, including the Sauropterygia, which featured pachypleurosaurs and nothosaurs, and the first plesiosaurs, as well as the highly successful ichthyopterygians, which appeared in Early Triassic seas and soon diversified to achieve very large body masses by the Middle Triassic.
The Final Volcanic Winter
The Triassic Period ended with a mass extinction, which was particularly severe in the oceans, where the conodonts disappeared, as did all the marine reptiles except ichthyosaurs and plesiosaurs, and invertebrates like brachiopods and molluscs were severely affected. The cause of the Late Triassic extinction is linked to huge volcanic eruptions that occurred as the supercontinent Pangaea began to break apart about 202 to 191 million years ago, forming the Central Atlantic Magmatic Province, one of the largest known inland volcanic events since the planet had first cooled and stabilized. The magmatism produced dense dyke swarms, with individual dykes up to 800 kilometers long, massive sill complexes, and lava fields that covered several hundred kilometers, and the period of magmatism was brief, lasting only about 1 million years. This intense igneous activity indicates widespread mantle melting, rather than a simple plume within the mantle, and the varied petrological composition of the CAMP magmatism reflects local contamination of the upper mantle by continental lithosphere, including partial melting of previously subducted slabs. The magmatism, with its large scale injection of carbon and sulphur into the atmosphere, precipitated volcanic winters, followed by longer-term climate warming and ocean acidification, which caused the end-Triassic mass extinction.
The Dawn of the Dinosaurs
The extinction event at the end of the Triassic allowed the dinosaurs to expand into many niches that had become unoccupied, and they became increasingly dominant, abundant, and diverse, remaining that way for the next 150 million years. The true Age of Dinosaurs is during the following Jurassic and Cretaceous periods, rather than the Triassic, but the seeds of their dominance were sown in the Late Triassic when the large predators known as rauisuchians and the armored herbivores known as aetosaurs were wiped out. Surviving plants that went on to dominate the Mesozoic world included modern conifers and cycadeoids, and the first turtles, like Proganochelys and Proterochersis, appeared during the Norian Age of the Late Triassic Period. The number of Late Triassic extinctions is disputed, with some studies suggesting that there are at least two periods of extinction towards the end of the Triassic, separated by 12 to 17 million years, but the evidence suggests that the Manicouagan impact, dated to 214±1 million years ago, preceded the end of the Triassic by approximately 10±2 million years and could not therefore be the immediate cause of the observed mass extinction. The Triassic Period, spanning 50.5 million years from 251.902 million years ago to 201.4 million years ago, was the first and shortest geologic period of the Mesozoic Era, and the seventh period of the Phanerozoic Eon, setting the stage for the rise of the dinosaurs and the eventual evolution of mammals.