5.1 Triassic period

The Triassic period kicked off the Mesozoic Era 252 million years ago. It followed Earth's largest mass extinction and lasted about 50 million years, setting the stage for dinosaurs and early mammals to evolve.

Triassic Earth had a hot, dry climate and one massive supercontinent called Pangaea. Life slowly recovered from the extinction, with archosaurs and early dinosaurs emerging on land, while marine reptiles and new coral reefs populated the seas.

Triassic period overview

• The Triassic period was the first geological period of the Mesozoic Era, spanning approximately 50 million years from 252 to 201 million years ago
• Triassic period is crucial in paleontology as it followed the Permian-Triassic extinction event, the most severe known mass extinction in Earth's history, and saw the early diversification of dinosaurs and mammals
• The Triassic is named after the three distinct rock layers (tri meaning three) found in Germany and northwestern Europe, though Triassic rocks are found worldwide

Age and duration of Triassic

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• The Triassic period began approximately 252 million years ago, immediately following the end-Permian extinction event
• It ended around 201 million years ago with the Triassic-Jurassic extinction event
• The Triassic lasted for a duration of approximately 50.6 million years, making it the shortest period of the Mesozoic Era

Triassic stages and boundaries

• The Triassic is divided into three epochs: Early Triassic (252-247 Ma), Middle Triassic (247-237 Ma), and Late Triassic (237-201 Ma)
• These epochs are further subdivided into stages, such as the Induan, Olenekian (Early Triassic), Anisian, Ladinian (Middle Triassic), Carnian, Norian, and Rhaetian (Late Triassic)
• The Permian-Triassic boundary is marked by the end-Permian extinction event, while the Triassic-Jurassic boundary is defined by the end-Triassic extinction event and the first appearance of the ammonite Psiloceras spelae

Triassic climate and geography

• The Triassic period was characterized by significant changes in Earth's climate and geography, largely influenced by the formation of the supercontinent Pangaea
• Triassic climate patterns were generally hot and dry, with seasonal monsoons and significant regional variations
• Sea levels fluctuated throughout the Triassic, with a general trend of rising sea levels during the Late Triassic

Pangaea supercontinent in Triassic

• During the Triassic, Earth's landmasses were united into a single supercontinent called Pangaea
• Pangaea extended from pole to pole, surrounded by the vast Panthalassa Ocean
• The configuration of Pangaea had a profound impact on Triassic climate and ocean circulation patterns

Climate patterns of Triassic

• The Triassic climate was generally hot and dry, with temperatures likely higher than those of today
• Pangaea's vast size and latitudinal extent led to strong seasonality and large temperature gradients between the equator and poles
• Monsoonal circulation patterns developed, with seasonal winds bringing heavy rainfall to some regions (Tethys coast) and causing arid conditions in others (interior Pangaea)

Sea level changes in Triassic

• Sea levels were generally low during the Early Triassic, following the end-Permian regression
• Throughout the Triassic, sea levels gradually rose, with a significant transgression occurring during the Late Triassic
• Rising sea levels led to the formation of extensive shallow marine environments, such as the Tethys Sea between Laurasia and Gondwana

Triassic flora and fauna

• The Triassic period saw a gradual recovery of life following the end-Permian extinction, with the diversification of various plant and animal groups
• Marine ecosystems were dominated by mollusks, corals, and early marine reptiles, while on land, conifers and ferns were common, and archosaurs, including early dinosaurs, began to appear
• The Triassic fauna laid the foundation for the iconic dinosaur-dominated ecosystems of the Jurassic and Cretaceous periods

Recovery from Permian-Triassic extinction

• The Permian-Triassic extinction event wiped out an estimated 95% of marine species and 70% of terrestrial vertebrate species
• Recovery from this mass extinction was gradual, with low diversity ecosystems persisting for several million years into the Early Triassic
• By the Middle and Late Triassic, ecosystems had largely recovered, with increased diversity and complexity

Triassic marine life

• Marine invertebrates, such as ammonites, bivalves, and gastropods, were common in Triassic seas
• Scleractinian corals appeared and began to build reef structures
• Marine reptiles, including ichthyosaurs, plesiosaurs, and placodonts, evolved and diversified throughout the Triassic

Triassic terrestrial plants

• Triassic floras were dominated by gymnosperm groups, such as conifers, cycads, and ginkgophytes
• Ferns and lycophytes were also common, especially in wet environments
• The first appearance of true mosses (Bryophyta) is recorded from the Triassic

Triassic terrestrial animals

• Synapsids, including early mammals and their relatives, survived the end-Permian extinction and continued to evolve during the Triassic (Lystrosaurus, Cynognathus)
• Archosauromorphs, including crocodilian ancestors and early dinosaurs, appeared and began to diversify
• Other notable Triassic tetrapods include temnospondyls (Mastodonsaurus), rhynchosaurs (Hyperodapedon), and dicynodonts (Kannemeyeria)

Archosaurs of Triassic

• Archosaurs, the group including crocodilians, pterosaurs, and dinosaurs, originated in the Early Triassic and diversified throughout the period
• Pseudosuchians, the crocodilian lineage, included large predatory forms such as Postosuchus and herbivorous aetosaurs like Desmatosuchus
• Avemetatarsalians, the bird lineage, included early pterosaurs (Eudimorphodon) and dinosauromorphs

Early dinosaurs in Triassic

• The first dinosaurs appeared in the Late Triassic, around 230 million years ago
• Early dinosaurs were relatively small (Eoraptor, Herrerasaurus) and coexisted with other archosaur groups
• Key dinosaur lineages, including sauropodomorphs (Saturnalia), theropods (Coelophysis), and ornithischians (Pisanosaurus), had their origins in the Late Triassic

Triassic mass extinctions

• The Triassic period is bookended by two major mass extinction events: the Permian-Triassic extinction at its beginning and the Triassic-Jurassic extinction at its end
• The end-Triassic extinction event saw the loss of many marine and terrestrial species, including some early dinosaur groups
• The causes of the end-Triassic extinction are still debated but may include volcanic activity, climate change, and ocean acidification

End-Triassic extinction event

• The end-Triassic extinction event occurred approximately 201 million years ago, marking the boundary between the Triassic and Jurassic periods
• It resulted in the extinction of an estimated 76% of marine species and 20-40% of terrestrial tetrapod families
• Groups that suffered major losses include conodonts, ammonites, bivalves, and some early dinosaur lineages (coelophysoids, basal sauropodomorphs)

Causes of end-Triassic extinction

• The exact causes of the end-Triassic extinction are still uncertain, but several factors have been proposed
• Volcanic activity associated with the Central Atlantic Magmatic Province (CAMP) likely played a significant role, releasing large amounts of CO2 and other greenhouse gases
• Rapid global warming, ocean acidification, and reduced oxygen levels in marine environments may have contributed to the extinction

Survivors of end-Triassic extinction

• Some groups, such as ichthyosaurs, plesiosaurs, and crocodyliforms, survived the end-Triassic extinction with relatively minor losses
• Dinosaurs, particularly theropods and sauropodomorphs, not only survived but thrived in the aftermath of the extinction
• Surviving groups likely had traits (e.g., fast growth rates, generalist diets) that allowed them to adapt to the changing environmental conditions

Triassic stratigraphy and geology

• Triassic strata are found worldwide, with significant outcrops in Europe, North America, and Asia
• The Triassic is named after the "trias" (three-part division) of rocks in Germany, consisting of the Buntsandstein, Muschelkalk, and Keuper formations
• Major geologic events during the Triassic include the breakup of Pangaea and the formation of the Central Atlantic Magmatic Province (CAMP)

Triassic rock formations

• Buntsandstein: a sequence of red sandstones and conglomerates deposited in terrestrial environments during the Early Triassic (Germany)
• Muschelkalk: a series of marine limestones and dolomites from the Middle Triassic (Germany)
• Keuper: a sequence of terrestrial sandstones, mudstones, and evaporites from the Late Triassic (Germany)
• Chinle Formation: a Late Triassic terrestrial sequence known for its rich vertebrate fossil assemblages (southwestern United States)

Triassic fossil localities

• Solnhofen Limestone: a Late Triassic Lagerstätte famous for its exceptionally preserved fossils, including the early bird Archaeopteryx (Germany)
• Ischigualasto Formation: a Late Triassic terrestrial sequence that has yielded numerous early dinosaur and archosaur fossils (Argentina)
• Madygen Formation: a Middle-Late Triassic sequence known for its diverse insect and plant fossils (Kyrgyzstan)
• Monte San Giorgio: a Middle Triassic marine sequence designated as a UNESCO World Heritage Site for its exceptional marine reptile and fish fossils (Switzerland/Italy)

Triassic geologic events

• Siberian Traps volcanism: a major flood basalt event coinciding with the Permian-Triassic boundary, likely contributing to the mass extinction
• Breakup of Pangaea: the supercontinent began to rift apart during the Late Triassic, forming the North Atlantic Ocean
• Central Atlantic Magmatic Province (CAMP): a large igneous province active during the Late Triassic, associated with the breakup of Pangaea and the end-Triassic extinction

Triassic and evolution

• The Triassic period saw significant evolutionary developments, as life recovered and diversified following the end-Permian extinction
• Many major animal and plant groups underwent adaptive radiations during the Triassic, filling newly available ecological niches
• The Triassic set the stage for the rise of the dinosaurs, which would go on to dominate terrestrial ecosystems for the remainder of the Mesozoic

Adaptive radiation in Triassic

• Archosauromorphs: this group, including crocodilians, pterosaurs, and dinosaurs, diversified into a wide range of forms and ecological roles during the Triassic
• Mammals: early mammal groups, such as morganucodonts and haramiyidans, evolved and diversified during the Triassic, laying the foundation for mammalian evolution
• Conifers: this group of gymnosperms underwent a significant radiation during the Triassic, adapting to various terrestrial environments

Evolutionary innovations of Triassic

• Amniotic eggs: the evolution of shelled eggs that could be laid on land allowed tetrapods to become fully terrestrial
• Endothermy: some Triassic synapsids (mammal ancestors) and archosaurs (bird ancestors) began to evolve features associated with endothermy, such as insulating coverings and high metabolic rates
• Hypsodont teeth: high-crowned teeth adapted for processing abrasive plant material evolved independently in several Triassic herbivore lineages (aetosaurs, rhynchosaurs, traversodontids)

Triassic and rise of dinosaurs

• Dinosaurs first appeared in the Late Triassic, around 230 million years ago
• Early dinosaur evolution was shaped by competition with other archosaur groups and the end-Triassic extinction
• Key anatomical features of dinosaurs, such as the elongated ankle bone (astragalus) and upright posture, likely contributed to their successful radiation in the Jurassic and Cretaceous

Triassic and human history

• Although the Triassic period ended over 200 million years ago, its study has had significant impacts on our understanding of Earth's history and has captured the public imagination
• The discovery of Triassic fossils in the 19th century played a key role in the development of paleontology and evolutionary theory
• Triassic rock formations are also important sources of economic resources, such as hydrocarbons and mineral deposits

Discovery of Triassic period

• The Triassic was first recognized as a distinct geological period by German geologist Friedrich August von Alberti in 1834
• Early pioneers of Triassic paleontology include William Conybeare, William Buckland, and Richard Owen, who described many iconic Triassic fossils from Europe
• The discovery of rich Triassic fossil deposits in North America, South America, and Africa in the late 19th and early 20th centuries expanded our understanding of Triassic life

Triassic in popular culture

• Triassic animals, particularly early dinosaurs and marine reptiles, have captured the public imagination and are frequently depicted in popular media
• Notable examples include the Coelophysis in Jules Verne's "Journey to the Center of the Earth" and the Postosuchus in the BBC series "Walking with Dinosaurs"
• Triassic-themed exhibits and displays are popular attractions at natural history museums worldwide

Economic resources from Triassic

• Triassic rock formations are important sources of hydrocarbon resources, particularly natural gas (Vaca Muerta Formation in Argentina, Montney Formation in Canada)
• Evaporite deposits from the Triassic, such as halite and gypsum, are mined for various industrial and agricultural applications (Mercia Mudstone Group in the United Kingdom)
• Triassic sandstones and conglomerates are often used as building stones and aggregate for construction purposes (Buntsandstein in Germany)