Recovery and the first dinosaurs
Triassic
Mesozoic Era · 251.9 – 201.4 million years ago
The Triassic Period ran from 251.9 to 201.4 million years ago, opening the Mesozoic Era. Over these 50 million years, life rebuilt itself from the worst mass extinction ever, on a hot supercontinent where no ice covered the poles.
Out of that recovery came an astonishing cast of newcomers: the first dinosaurs, the first pterosaurs, the first turtles and the earliest close relatives of mammals, along with marine reptiles such as ichthyosaurs. Yet for most of the Triassic, dinosaurs were bit players, and it took another mass extinction to hand them the world.
Key facts
- Began
- 251.9 MaMillion years ago
- Ended
- 201.4 MaMillion years ago
- Duration
- 50.5 million years
- Era
- Mesozoic“Middle life”
- Global temperature
- ~27°CRoughly 24–29°C · today 14.5°C
- Plants on land
- Forests
- Atmospheric CO₂
- ~1,000–2,000+ ppm (several × pre-industrial); uncertain
- Oxygen
- Possibly lower than today's 21%; estimates vary widely
- Sea level
- Fairly low, with no polar ice caps
- Continents
- Pangaea intact but starting to rift late in the period
- Signature life
- Lystrosaurus, early dinosaurs, ichthyosaurs, pterosaurs
- Began with
- Survivors of the end-Permian extinction
- Ended with
- The end-Triassic extinction, linked to CAMP volcanism
Ages follow the International Chronostratigraphic Chart (ICS). Global temperatures are rough reconstructions after Scotese et al. (2021); ancient CO₂, oxygen and sea-level values carry large uncertainties.
Epochs of the Triassic
- Early Triassic251.9 Ma – 247.2 Ma
- Middle Triassic247.2 Ma – 237 Ma
- Late Triassic237 Ma – 201.4 Ma
Continents and oceans
Pangaea reached its fullest extent in the Triassic, a single landmass stretching from pole to pole. Because the continents were joined, land animals could walk almost anywhere, and similar animals turn up in rocks from South Africa to Antarctica, India and China.
The global ocean Panthalassa covered the rest of the planet, while the Tethys Ocean cut a great wedge into Pangaea's eastern side. Late in the period, long rift valleys began to tear the supercontinent apart between North America and Africa, filling with lakes and sediments that hint at the Atlantic Ocean to come.
Climate and atmosphere
The Triassic was a hothouse world without polar ice. The Early Triassic in particular seems to have been punishingly hot, and some studies suggest tropical seas were too warm for many animals to survive. Pangaea's interior was largely arid, with strong seasonal monsoons near the coasts.
Around 234 to 232 million years ago, the climate abruptly turned much wetter for a time. This Carnian Pluvial Episode, probably triggered by large volcanic eruptions in what is now western North America, reshaped ecosystems on land and sea and coincided with the early spread of dinosaurs.
Life in the Triassic
After the Great Dying, recovery was slow, taking several million years. When ecosystems did rebuild, they were filled with new kinds of animals, many of them reptiles, alongside surviving synapsids.
On land
In the Early Triassic, the stocky, tusked dicynodont Lystrosaurus was one of the most widespread land animals. Later, crocodile-line archosaurs such as rauisuchians, armoured aetosaurs and phytosaurs dominated. The first dinosaurs, including Eoraptor and Herrerasaurus, appeared around 231 million years ago, and by the end of the period plant-eaters like Plateosaurus and nimble predators like Coelophysis were common.
Mammal relatives and turtles
Cynodonts gave rise to the mammaliaforms, small, furry, probably nocturnal animals such as Morganucodon, close relatives of true mammals. The first turtles appeared too, including Odontochelys from China, which had a shell only on its belly.
In the seas
Marine reptiles radiated rapidly: ichthyosaurs appeared in the Early Triassic, and some Late Triassic species such as Shonisaurus were around 15 metres long. Nothosaurs, shellfish-crushing placodonts and the long-necked Tanystropheus also lived in coastal waters, and modern-type stony corals began building reefs.
In the air
Pterosaurs became the first vertebrates to achieve powered flight during the Late Triassic. Early forms such as Eudimorphodon from Italy were small, toothy and long-tailed.
Timeline of key events
- 251.9 Ma
Triassic begins
A sparse, hot world emerges from the end-Permian mass extinction.
- 251 Ma
Lystrosaurus spreads across Pangaea
This hardy dicynodont becomes one of the most common land animals of the earliest Triassic.
- 248 Ma
First ichthyosaurs
Reptiles return to the sea, with early ichthyosaurs appearing in what is now China and elsewhere.
- 234 Ma
Carnian Pluvial Episode
A wetter interval of a million years or more transforms ecosystems and climate worldwide.
- 231 Ma
Early dinosaurs in Argentina
Eoraptor and Herrerasaurus live in the Ischigualasto basin, among the oldest well-dated dinosaurs.
- 214 Ma
Manicouagan impact
An asteroid strikes what is now Quebec, leaving a crater about 100 kilometres wide, but causes no mass extinction.
- 201.4 Ma
End-Triassic mass extinction
CAMP volcanism triggers a mass extinction that clears the way for dinosaurs.
How the Triassic ended
About 201.4 million years ago, as Pangaea began to split, the Central Atlantic Magmatic Province (CAMP) erupted floods of lava across what are now the Americas, Africa and Europe. The gases released are thought to have caused rapid warming and ocean acidification, triggering one of the five great mass extinctions.
Roughly three-quarters of species may have vanished. Conodonts disappeared for good, and most crocodile-line archosaurs died out. Dinosaurs survived largely intact, and with their rivals gone, they went on to dominate the Jurassic.
Where to see Triassic fossils
Ghost Ranch in New Mexico has yielded hundreds of skeletons of Coelophysis from a single bone bed, while nearby Petrified Forest National Park in Arizona preserves huge fossil logs and Late Triassic reptiles. In Argentina, the Ischigualasto Formation, known as the Valley of the Moon, holds some of the oldest dinosaurs, including Eoraptor and Herrerasaurus.
The Karoo of South Africa records Lystrosaurus and the recovery after the Great Dying, and Trossingen in Germany is famous for Plateosaurus. Monte San Giorgio on the Swiss–Italian border is a UNESCO site celebrated for Middle Triassic marine reptiles and fishes.
Surprising facts about the Triassic
- For their first 30 million years or so, dinosaurs were mostly small and uncommon, outnumbered by crocodile-line reptiles and other groups.
- Lystrosaurus fossils have been found in South Africa, India, China and Antarctica, which helped confirm that these lands were once joined in Pangaea.
- A skull of Coelophysis travelled into space aboard the Space Shuttle Endeavour in 1998 and visited the Mir space station.
- The early turtle Odontochelys had a fully formed shell on its belly but none on its back, offering a glimpse of how the turtle shell evolved.
- Tanystropheus had a neck about three metres long, roughly half the length of its entire body.
- The name Triassic refers to the threefold division of these rocks in Germany into red sandstones, marine limestones and colourful mudstones, described by Friedrich von Alberti in 1834.
Where it sits in deep time
The globe beside this article shows Earth 230 million years ago, reconstructed from the PALEOMAP paleo-elevation models. Step to another period and watch the continents drift into place.