The Triassic Period: A Time of Transition and Evolution

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triassic period

The Triassic Period is the first period of the Mesozoic Era.

It spanned over a period of 51 million years, starting from the end of the Permian Period of the Paleozoic Era (about 252 million years ago) till the beginning of the Jurassic Period (about 201 million years ago).

The Triassic Period was named after a succession of three (tri) rock layers found in Southern Germany that were deposited during that period.

Friedrich August von Alberti named the period in 1834. 

The Triassic Period began right after the Great Permian extinction wiped out up to 90% of life on Earth, leaving the planet bare and desolate.

What followed was a period of significant change as the survivors of the Permian extinction began to diversify again, evolving rapidly into new forms to adapt to the planet’s changing conditions. 

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The global climate was hot and dry during the Triassic.

Earth’s continents formed a single landmass called Pangea which started to drift apart towards the end of the period, causing changes in climatic conditions.  

The Triassic Period saw the rise of reptiles to become the dominant vertebrates in Earth’s emerging ecosystems.

The dinosaurs, a group of archosaurs that would later become the dominant terrestrial group of the Mesozoic Era, emerged during the Triassic.

Other reptilian groups, including the crocodilians and the flying reptiles, also emerged during this period.

Earth’s recovering plant and animal life would later suffer another mass extinction barely 50 million years after the first one, bringing the Triassic Period to a close.

In this article, we’ll explain the timeline of the Triassic Period, the climate and geography, and the key events that shaped the period. 

Timeline of the Triassic Period

Sydney, Australia lies on Triassic shales and sandstones | Sardaka via Wikipedia (CC BY 3.0)

The Triassic Period is the first and shortest of the three periods that make up the Mesozoic Era.

The Period began about 252 million years after the Mesozoic Era ended and came to an end 51 million years later with the Triassic-Jurassic extinction event.

This means the period started and ended with an extinction event. 

The entire 51 million years period is further divided into three epochs, namely the Early Triassic, Middle Triassic, and Late Triassic epochs, characterized by significant changes in earth’s geography, the evolution of organisms, and shifts in climatic conditions.

The various events that happened during these sub-eras are highlighted below.

Early Triassic Epoch (251-247 Million Years Ago)

Archosaur Prestosuchus | MR1805 via Getty Images

The Early Triassic Epoch, which began 251 million years ago, follows right after the events of the end Permian extinction, which affected both aquatic and terrestrial lifeforms.

By the time the epoch began, up to 90% of marine species and about 70% of terrestrial species from the previous era had disappeared. 

Despite being hard hit by the last extinction event, the marine life of the Early Triassic still had a few marine reptiles left.

Fishes and marine invertebrates were also starting to reestablish themselves after their initial decline. 

The Early Triassic Epoch was characterized by a hot and arid climate. On land, there was a limited range of plants and animals.

Terrestrial life was still quite primitive when the Permian extinction occurred, and it took a while for the primitive plants and animals to recover.

However, some reptiles, including archosaurs and early dinosaurs, began to emerge towards the end of the Early Triassic Epoch.

Middle Triassic Epoch (247-237 million years ago):

Green Cycad Plant | ViniSouza128 via Getty Images

The Middle Triassic Epoch is often described as a transitional period.

That’s because the marine and terrestrial ecosystems of the Triassic moved beyond recovery to diversification during this period.

Climatic conditions were generally warmer and more humid compared to the Early Triassic. 

As the marine ecosystems continued to recover, there was a diversification of existing groups of organisms and the emergence of new ones.

Coral reefs reappeared, and ammonoids became more diverse.

Bivalves and gastropods also increased.

The marine reptiles that survived the Paleozoic, such as ichthyosaurs and Nothosaurus, became more common.

New reptilian groups, such as the placodonts and marine crocodylomorphs, also emerged during this period.

Terrestrial ecosystems continued to evolve during the Middle Triassic.

More advanced plant groups such as the cycads, ginkgos, and conifers evolved and diversified during this period.

Reptilian groups (especially the archosaurs) diversified further on land as well.

Therapsids, a group of mammal-like reptiles considered the ancestors of mammals, flourished during this period. 

Late Triassic Epoch (237–201 Million Years Ago)

Giant Ichthyosaurus | 3dsam79 via Getty Images

The last 36 million years of the Triassic Period were characterized by several important geological and biological events.

The Triassic climate remained warm, but there was a shift towards increased aridity towards the end of the Triassic Period. 

Large marine predators such as ichthyosaurs and crocodylomorphs evolved as part of the ongoing diversification of marine reptiles.

The Late Triassic is noted as the peak of the ammonoids’ diversity and abundance. 

Pangea broke up, and the continents drifted apart, causing some major changes in the Late Triassic terrestrial ecosystems.

Non-flowering plants remained the dominant plant group throughout this period. 

The dinosaurs became more established towards the end of the period and evolved into more diverse forms.

Archosaurs, such as crocodiles and early birds, thrived as well.  Small mammals were also present but were limited in their diversity. 

Climate and Geography of the Triassic Period

Illustration of Plants from the Triassic period | Nastasic via Getty Images

During the first few million years of the Triassic Period, all the continents were consolidated into a single supercontinent known as Pangaea.

This unified landmass was located close to the equator and surrounded by a single large ocean called Panthalassa

Due to the size of the supercontinent, ocean currents had a limited effect on the interior regions of Pangaea.

This resulted in extreme continental climates during the Early Triassic. The earth’s climate was generally hot and arid.

There were widespread deserts and limited vegetation cover in most places. 

Pangaea began to break apart during the Middle Triassic. Two separate land masses were formed as a result of the continental rift.

The northern continent, Laurasia, included the landmass of North America, Europe, and Asia.

The landmass to the south is known as Gondwana, and it was composed of present-day South America, Africa, Australia, Antarctica, and the Indian subcontinent.

The breaking up of the supercontinent was accompanied by significant volcanic activities, especially during the early stages.

Mountain-building processes were also ongoing on the west coast of North America.

Volcanoes erupted, releasing large amounts of lava and greenhouse gases such as carbon dioxide into the air. 

Middle Triassic marginal marine sequence, southwestern Utah | Wilson44691 via Wikipedia

These volcanic activities and the changes in the sea level during this period shaped the climate of the Middle Triassic.

The planet became generally warmer and more humid compared to the Early Triassic.

Plant life continued to recover, leading to moisture retention that further influenced the climate patterns across various locations. 

Although there were still arid regions, forestlands expanded, and more areas began to experience seasonal rainfall.

The global climate remained relatively warm for the rest of the Triassic, but there were regional variations from place to place. 

Sea levels fluctuated from the Middle to Late Triassic Period.

This fluctuation was mainly due to the tectonic movements associated with the breakup of Pangaea and the ongoing volcanic activities across the planet. 

These sea-level changes affected the distribution of marine environments.

The interior of the continents was flooded, affecting connectivity between landmasses.

This created new environments, such as moist river and lake habitats with gymnosperm forests.

However, arid environments with massive dunes still persisted in some regions. 

Towards the end of the Triassic Period, the climate became more seasonal, with distinct wet and dry seasons.

Some regions (especially places closer to the coasts) experienced monsoonal climates. 

Key Events and Developments of the Triassic Period

The Triassic Period began with one of the most devastating mass extinction events in Earth’s history.

Over the next 51 million years, the planet went through various changes that shaped the Triassic Period and set the stage for the next phase of Earth’s history for the rest of the Mesozoic Era.

The following are some of the most notable events of the Triassic Period. 

Recovery and Diversification of Lifeforms

A school of Masu Salmon try to evade a group of Ichthyosaurs | CoreyFord via Getty Images

The Triassic Period is considered a period of recovery and diversification as the earth entered a new phase in its evolutionary history.

Three categories of organisms can be identified from the Triassic Period.

They include those that survived the Permian extinction, new species that emerged after the extinction but didn’t survive the Triassic, and the animal groups that persisted till the end of the period.

All of these groups evolved to take advantage of the new ecological opportunities present in the marine and terrestrial ecosystems. 

Continental Breakup

Pangea or Pangaea | Ianm35 via Getty Images

Pangaea, the supercontinent that existed during the Triassic, began to break apart during the Triassic Period.

Continental rifting caused by the spreading sea floor at the mid-oceanic ridge at the bottom of the Tethys Sea separated Pangea and Gondwana in the South and Laurasia in the North. 

Climatic Changes

Climate change | appledesign via Getty Images

The Triassic Period was characterized by climatic fluctuations. The Early Triassic was hot and arid.

The Middle Triassic saw a shift towards warmer and more humid climates.

But by the end of the Triassic Period, the climate became arid again with the expansion of dry environments.

These events shaped the terrestrial and aquatic landscape of the Triassic Period. 

Triassic-Jurassic Extinction Event

The Triassic Period ended with another significant mass extinction event.

This mass extinction event, known as the Triassic-Jurassic extinction event, resulted in the disappearance of various reptile groups.

It also paved the way for dinosaurs to become the apex predators of the Jurassic Period.

Major Groups of Organisms in the Triassic Period

The Triassic Period was a time of rejuvenation for the animal life of the planet.

The groups that survived the Great Dying started repopulating the planet, and many of them entered into new ecological niches that supported the rise of new creatures.

Some of the major groups of organisms of the Triassic Period include: 


Therapsids | Elenarts108 via Getty Images

The Triassic was a time of significant development for a group of mammal-like reptiles known as the therapsids.

These reptiles, often referred to as the ancestors of modern mammals, were a transitional group between reptiles and true mammals.

They diversified during the Triassic, representing an important step in the evolution of mammals.


Crocodylomorph | Aunt_Spray via Getty Images

Archosaurs were a group of reptiles that played a significant role in the Triassic ecosystems.

Although the therapsids were the dominant group during the Early Triassic, the archosaurs soon overtook them.

The group included crocodylomorphs (early relatives of crocodiles), various forms of early birds, and dinosaurs.

Archosaurs diversified during the Triassic and would later give rise to the dominant archosaur groups of the Jurassic and Cretaceous periods.

Marine Reptiles 

Plesiosaur vs. Octopus | Daniel Eskridge via Getty Images

Various reptiles adapted to the new marine ecosystems of the Triassic emerged during this period.

Some of the most notable examples include ichthyosaurs, a group of marine reptiles that resembled dolphins.

Plesiosaurs (long-necked reptiles) also emerged as the apex predators of the Triassic ecosystems. 


Arizonasaurus from the Triassic era | Warpaintcobra via Getty Images

Reptiles remained the dominant group of the Triassic Period, and they evolved into various forms.

One of the new entrants by the beginning of the Triassic was the early dinosaurs.

They were initially small bipedal reptiles but soon evolved into various forms.

The dominance of dinosaurs would continue through the Jurassic and the Cretaceous periods when they became fully established. 

Triassic Plants 

Mossy branch | keiichihiki via Getty Images

Triassic plants did not undergo significant evolution during the Triassic.

Due to the harsh climatic conditions in the interior of Pangea, very few plants were able to survive and adapt.

In the higher latitudes, gymnosperms began to emerge during the Middle Triassic.

Mosses and ferns were also abundant around the coastal regions. 


Grasshopper | Robert Winkler via Getty Images

Many insect groups survived the Permian extinction but didn’t diversify significantly during the Triassic.

New groups, such as the grasshoppers, also emerged during this period.

The absence of forest habitats stifled the evolution of insects throughout the Triassic. 

Notable Species from the Triassic Period

In the Triassic marine and terrestrial environments, various animal species rose to prominence and became quite abundant.

Some of these species are significant because they’re among the earliest members of the group or were the most dominant species within their ecological niche. 


Herrerasaurus | leonello via Getty Images

Herrerasaurus is one of the earliest known dinosaurs.

Fossil records show that this basal theropod lived in present-day South America during the Cretaceous Period

It was a bipedal carnivore with a slender body, sharp teeth, and relatively long arms for grasping prey. 


Peteinosaurus | MR1805 via Getty Images

Peteinosaurus was a small flying reptile.

This winged creature was one of the first pterosaurs that lived during the Late Triassic.

Peteinosaurus had a long, narrow skull with sharp teeth.

It probably fed on insects and other small prey.


Coelophysis | MR1805 via Getty Images

Coelophysis lived in North America during the Late Triassic.

It was a small to medium-sized dinosaur and one of the most well-known early theropods from the Triassic: 


Eoraptor | Jurassic Park Institute via Jurassic Park Wiki

Eoraptor lived in Western Gondwana (present-day South America) during the Late Triassic.

It was a small bipedal dinosaur known to have exhibited both reptilian and dinosaurian characteristics.

This makes it an important species for our understanding of early dinosaur evolution.


Gage Beasley Prehistoric’s Nothosaurus Concept

Nothosaurus was a marine reptile that lived during the Triassic about 240 million years ago.

It had a streamlined body, elongated neck, and paddle-like limbs.

These adaptations made it possible for the Nothosaurus to live a semi-aquatic lifestyle preying on fish and other small marine organisms.


Placodus | CoreyFord via Getty Images

Placodus was a marine reptile known for its heavily armored body.

It lived during the Middle Triassic about 240 million years ago.

The Placodus was most likely a terrestrial reptile that inhabited coastal marine environments and ventured into the sea for food.


Proterosuchus | Photo via Fossil Wiki

Proterosuchus is a primitive relative of the crocodiles.

It was an archosaur that lived in the Early Triassic.

Proterosuchus is one of the earliest archosaurs ever discovered. 


Eozostrodon | Photo via Extinct Animals Wiki

The  Eozostrodon is one of the earliest true animals ever found.

This shrew-like creature laid eggs, but experts believe it was capable of feeding its young with milk. 


Plateosaurus | MR1805 via Getty Images

Plateosaurus was one of the first herbivorous dinosaurs ever found.

This bipedal herbivore lived during the Late Cretaceous Period in an area that is now central and northern Europe.

The Triassic Rejuvenation and its Impact on Evolution

Moschops therapsid, mammal diversification | Warpaintcobra via Getty Images

The ecological and evolutionary rebound period following the devastating Permian-Triassic mass extinction event was an important time in the earth’s evolutionary history.

The organisms that survived the extinction events and the new ones that emerged lived during a time characterized by the gradual recovery and reconstruction of ecosystems. 

New food webs and ecological interactions emerged as the Triassic species diversified and adapted to the changing environments.

This laid the groundwork for the complex ecological dynamics that would allow the evolution of new species throughout the Mesozoic Era.

After the Permian extinction, marine reptiles quickly rose to fill the vacant marine ecosystems that had been heavily impacted by the extinction.

Species like ichthyosaurs and plesiosaurs evolved and thrived in the Early Triassic, becoming the top predators in the earth’s oceans.

The most notable animal group that emerged during this period of rejuvenation was the dinosaurs.

With the disappearance of the main dominant reptilian groups, such as the para reptiles and synapsids, the dinosaurs gradually evolved to fill the vacant terrestrial ecosystems of the Triassic.

This set the stage for them to flourish and ultimately evolve to dominate the land for the next millions of years.

The Triassic rejuvenation has also played a significant role in the evolution of early mammals and their relatives.

The mammal-like reptiles known as therapsids, which had survived the mass extinction, diversified during the Early Triassic.

These therapsids exhibited traits that were transitional between reptiles and mammals.

Some of them eventually evolved into the first true mammals in the subsequent periods of the Mesozoic Era. 

Extinction Events and Their Effects on the Triassic Period

Extinction | azgraphic via Getty Images

The Triassic Period is sandwiched between two major extinction events.

Expectedly, these two events had an impact on how life evolved and progressed during this period of Earth’s history and in the eras that followed. 

The mass extinction at the beginning of the Triassic created vast ecological vacancies.

These ecological gaps provided ample opportunities for the survivors and newly emerging species to exploit unoccupied ecological niches.

The empty habitats and vacant ecological roles allowed for the diversification and radiation of various groups.

This led to the evolution of new forms of life.

The Triassic Period also ended dramatically with the Triassic-Jurassic extinction.

Although this event was relatively moderate compared to the Great Dying, it undid some of the evolutionary progress made during the period.

Several groups, including various reptilian and amphibian groups, were wiped out during this period.

The event wiped out all the conodonts along with more than 23% of marine genera.

On land, several archosaurs, crocodylomorphs, pterosaurs, and dinosaur groups became extinct as well. 

However, the disappearance of these reptilian groups also came with some benefits as it paved the way for the dominance of dinosaurs in the subsequent periods of the Mesozoic Era, heralding the dawn of the dinosaurs. 


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