The Mesozoic Era: Exploring Life’s Most Prolific Period

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mesozoic era

Also called the “Age of the Reptiles,” the Mesozoic Era is the earth’s second-to-the-last era of geological history that lasted from approximately 252 to 66 million years ago.

This era was called the Age of the Reptiles because of the earth’s abundance of reptiles at the time, particularly dinosaurs that ruled the earth and sky.

In addition to the rise of the dinosaurs, other significant events during the Mesozoic Era include the diversification of mammals, the evolution of birds, the first appearance of flowering plants, and the breakup of the supercontinent Pangaea.

During this era, the earth’s landmasses formed a single massive continent with a distinct shape and geography.

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This “supercontinent” was called Pangea, derived from Greek, meaning “all lands.”

Pangea formed from the collision of several smaller continents, including North America, South America, Africa, Australia, and Antarctica.

The supercontinent began to break apart during the Jurassic period, eventually separating into the continents we know today. 

The end of the Mesozoic Era witnessed a mass extinction event, which wiped out the dinosaurs and many other species of plants and animals.

Because of how far back this period is, there must have been a lot that the average person does not know about.

However, this article will focus on the various happenings of the Mesozoic Era and other important information about this period.

Timeline of the Mesozoic Era

The Mesozoic Era lasted from about 252 to 66 million years ago and further separated into three primary periods and several sub-eras.

This portion of the article wil cover the various periods and their sub-eras.

1. The Triassic Period

Antique illustration, geology and fossils: Triassic, Keuper era | ilbusca via Getty Images

As the first and shortest period of the Mesozoic Era, the Triassic Period lasted from 252 to 201 million years ago.

Friedrich August von Alberti named this period in 1834, and he got the name from the three distinct layers of rock popular in Southern Germany, which formed during the period.

One of the primary geological facts about this period was that the supercontinent slowly began to break apart, with rifts in what is now the Atlantic Ocean.

This process caused massive volcanic eruptions, which released enormous amounts of carbon dioxide and other gases into the atmosphere, leading to significant climate change.

The Lower Triassic Era

Early Triassic sandstone (Buntsandstein) near Stadtroda, Germany | ArtMechanic via Wikipedia (CC BY-SA 3.0)

The first sub-era of the Triassic Period was the Lower Triassic Era.

It was a time of significant change and upheaval in Earth’s history, characterized by a major extinction event and the emergence of new groups of animals and plants.

The Lower Triassic is famous for the aftermath of the Permian-Triassic extinction, the largest mass extinction event in Earth’s history.

This event was a combination of factors, including massive volcanic eruptions and global warming, which wiped out approximately 96% of marine and 70% of terrestrial species.

As a result of the extinction, many ecological niches became vacant, providing opportunities for new groups of organisms to emerge and diversify.

Many new groups of animals and plants emerged, filling the ecological niches left vacant by the extinction.

The earliest dinosaurs evolved during the Lower Triassic, though they remained relatively small and insignificant until later in the Mesozoic.

One of the most significant biological events of the Lower Triassic was the emergence of the first marine reptiles, including the ichthyosaurs and sauropterygians.

These groups of animals would go on to dominate the oceans throughout much of the Mesozoic Era, and their evolution was likely influenced by the changing oceanic conditions resulting from the break-up of Pangaea.

The Lower Triassic also witnessed a global warming event, which was one of the primary causes of the Permian-Triassic extinction.

As the Earth’s climate warmed, sea levels rose, and the oceans became more acidic.

These changes affected marine life, causing widespread extinctions and reshaping the evolutionary trajectory of many groups of animals.

As the Lower Triassic progressed, the Earth’s climate began to cool, and the oceans became more oxygenated.

The Middle Triassic Era

Photo: Mark A. Wilson (Department of Geology, The College of Wooster) via Wikipedia

The Middle Triassic Era occurred 247 and 237 million years back, following the Permian-Triassic extinction event.

During the Middle Triassic, the supercontinent Pangaea continued to shift, and the Tethys Ocean began to open up.

This shift also resulted in the formation of extensive rift basins in present-day North America, Europe, and Asia.

These basins contained thick layers of red sandstone, siltstone, and shale, ideal conditions for fossil preservation.

The Middle Triassic saw the emergence and diversification of many new species of plants and animals.

One of the most significant events was the rise of the archosaurs, a group of reptiles that included the ancestors of crocodiles, pterosaurs, and dinosaurs.

The Middle Triassic also saw the diversification of marine life, including the emergence of new groups of mollusks, such as ammonites and bivalves, and the evolution of marine reptiles, such as ichthyosaurs and sauropterygians.

Other animals that emerged during this era were amphibians and reptiles, including the rhynchosaurs, a group of beaked herbivorous reptiles, and the phytosaurs, a group of crocodile-like predators that inhabited freshwater environments.

The Upper Triassic Era

Late Triassic Steigerwald Formation and overlying Hassberge Formation in Schönbuch, Germany | Johannes Baier via Wikipedia (CC BY-SA 3.0)

The Upper Triassic is the final sub-era of the Triassic Period, which lasted from approximately 237 to 201 million years ago.

During the Upper Triassic, the supercontinent Pangaea continued to break apart, forming new ocean basins and the separation of the northern and southern landmasses.

This tectonic activity also led to new mountain ranges, including the Appalachian Mountains and the Central Atlantic Magmatic Province.

Volcanic activity was also prevalent during the Upper Triassic, with the Wrangellia flood basalts eruption in what is now western North America.

These volcanic eruptions affected the earth’s climate, releasing large amounts of carbon dioxide and other greenhouse gases into the atmosphere.

The Upper Triassic was a time of generally warm and dry climates, with large areas of the world experiencing arid conditions.

However, some regions experienced wetter conditions, particularly in the high latitudes.

The warm and dry conditions of the Upper Triassic led to the development of extensive deserts, such as the famous Chinle Formation of the southwestern United States.

These deserts were home to many reptiles, including the armored aetosaurs and the long-necked tanystropheids. 

The Upper Triassic was a time of significant evolutionary developments, with the diversification of many major groups of reptiles, including dinosaurs, crocodiles, and pterosaurs.

During this time, dinosaurs began to radiate and diversify, with the emergence of several new lineages, including the theropods, sauropodomorphs, and ornithischians.

In addition to the diversification of reptiles, the Upper Triassic also saw the emergence of the first mammals, small, shrew-like animals.

2. The Jurassic Period

Brachiosaurus, ankylosaurus and triceratops in the valley at the lake | Orla via Getty Images

One of the most well-known phases of the Mesozoic Era is the Jurassic Age, which lasted from 201 to 145 million years ago and was marked by the prevalence of dinosaurs.

However, the Jurassic was also a time of significant geological and biological change, marked by the emergence of new species, the diversification of existing groups, and the breakup of the supercontinent Pangaea.

Like the Triassic Period, the Jurassic Period also split into three stages: Early Jurassic, Middle Jurassic, and Late Jurassic.

The Early Jurassic Era

Folded Lower Jurassic limestone layers of the Doldenhorn nappe at Gasteretal, Switzerland | Woudloper via Wikipedia (CC BY-SA 1.0)

The Early Jurassic period is the first sub-era of the Jurassic period, which lasted from approximately 201 to 174 million years ago.

During the Early Jurassic period, the Earth’s continents continued to break apart from the supercontinent of Pangaea, which had started to split during the Late Triassic period.

This era also witnessed a warm and humid climate, with sea levels rising and falling in response to changes in temperature and ocean currents.

The Early Jurassic period was a time of rapid diversification and radiation of many groups of animals and plants.

One of the most notable events was the emergence of the first birds from small theropod dinosaurs.

These early birds, such as Archaeopteryx, had feathers and could fly, although they still retained many dinosaur-like features. 

Dinosaurs continued to diversify during the Early Jurassic, with the emergence of new species such as Dilophosaurus, a large carnivorous dinosaur with a distinctive double crest on its skull.

On land, ferns, cycads, and conifers dominated the flora of the Early Jurassic, with a few angiosperms (early flowering plants) beginning to emerge.

Bennettitales, which had flower-like structures but weren’t flowering plants, also emerged during this time.

The Middle Jurassic Era

Middle Jurassic strata in Neuquén Province, Argentina | Damián H. Zanette via Wikipedia (CC BY-SA 4.0)

The Middle Jurassic is a sub-era of the Jurassic Period, which lasted from approximately 174 million to 163 million years ago.

This was a time of significant diversification and evolution of many groups of organisms, including dinosaurs, mammals, and plants.

Dinosaurs continued to thrive during the Middle Jurassic, with many new species emerging and diversifying.

Some dinosaurs of the Middle Jurassic included the stegosaurs, such as Stegosaurus and Kentrosaurus, and the theropods, such as Allosaurus and Ceratosaurus.

These dinosaurs were some of the largest and most formidable predators of their time, and they played a crucial role in shaping the ecology of the period.

Mammals continued to evolve during the Middle Jurassic, although they remained small and relatively unimportant in the ecosystem.

Many early mammal species were nocturnal and fed on insects and small invertebrates.

There was also a significant plant life evolution and diversification during the Middle Jurassic.

Enormous sequoia, cypress trees, ferns, horsetails, and cycads, predominated in the forests of the time.

These plants supported various herbivorous dinosaurs, which in turn sustained a variety of predators.

The Late Jurassic Era

The Late Jurassic Era was the final sub-era of the Jurassic Period and a period of significant change and evolution that lasted from 163 to 145 million years ago.

Although still relatively small and insignificant during the Late Jurassic, mammals began to evolve and diversify.

While dinosaurs continued to dominate the landscape, the rise of mammals during the Late Jurassic set the stage for their eventual success and diversification in the following periods.

Some of the most well-known dinosaurs from the Late Jurassic include the Diplodocus, Brachiosaurus, Archaeopteryx, etc.

3. The Cretaceous Period

Parasaurolophus from the Cretaceous era | Warpaintcobra via Getty Images

The Cretaceous Period was the last period of the Mesozoic Era, lasting from 145 to 66 million years ago.

During the Cretaceous Period, the Earth’s climate was generally warm and humid, with high carbon dioxide levels in the atmosphere.

The continents continued to drift apart, leading to the emergence of new land masses.

This period brought several significant changes in the Earth’s geography and the evolution of more dinosaurs and plants.

Unlike the other periods of the Mesozoic Era, the Cretaceous Period has only two sub-eras.

Climate and Geography Of the Mesozoic Era

Brachiosaurus, Velociraptor, Triceratops, and Parasaurolophus in nature | Orla via Getty Images

The climate of the Mesozoic Era was marked by significant shifts, which affected the evolution and diversification of life on Earth.

During the Triassic Period, the earth’s climate was generally arid, with some regions experiencing desert conditions.

However, by the end of the Triassic, the weather began to shift, and the earth experienced warmer and more humid conditions.

During the Jurassic Period, the earth’s climate was generally warm and humid, with high carbon dioxide levels.

This led to the proliferation of lush forests of ferns, cycads, and conifers, which covered much of the land.

The Cretaceous Period saw a continuation of the warm and humid conditions of the Jurassic, with high levels of carbon dioxide in the atmosphere.

However, towards the end of the Cretaceous, the climate began to cool and dry.

As mentioned, the changing climate of the Mesozoic Era affected the evolution and diversification of life on Earth.

For example, the Jurassic’s more humid conditions allowed dinosaurs to diversify and dominate the land.

In contrast, cooler and drier conditions at the end of the Cretaceous may have contributed to their eventual extinction.

Pangea | Ianm35 via Getty Images

At the beginning of the Mesozoic Era, the Earth’s continents were a single supercontinent known as Pangaea.

This supercontinent was surrounded by a vast ocean called Panthalassa.

However, as the Mesozoic progressed, Pangaea began to break apart, and the various continents moved away from each other.

By the end of the Mesozoic, the continents had separated into the familiar shapes we recognize today.

The breakup of Pangaea had significant implications for the evolution of life on Earth.

As the continents drifted apart, they created new habitats and environments, which allowed organisms to diversify and evolve in new ways.

For example, separating South America from Africa created new opportunities for the evolution of unique South American mammals, such as marsupials.

Major Organism Groups of the Mesozoic Era

Although called the Age of Reptiles due to the dominance of various groups of reptiles during this period, the Mesozoic Era saw the emergence and diversification of many other significant groups of organisms that shaped the evolution of life on Earth.

Here are some of the major organism groups of the Mesozoic Era:

1. Dinosaurs

Brachiosaurus, Tyrannosaurus, Parasaurolophus, and Triceratops in the forest | Orla via Getty Images

Dinosaurs are the most famous group of organisms from the Mesozoic Era, and they evolved during the Triassic period and continued to diversify and dominate the land during the Jurassic and Cretaceous periods.

2. Pterosaurs

Pterosaur flying over a landscape | Warpaintcobra via Getty Images

Pterosaurs were flying reptiles that evolved during the Late Triassic period and continued to thrive during the Jurassic and Cretaceous periods.

They were the first vertebrates to evolve powered flight and had a wingspan of up to 10 meters (33 feet). Pterosaurs fed on various prey, including fish, insects, and small vertebrates.

3. Marine Reptiles

Prehistoric mosasaur | MR1805 via Getty Images

The Mesozoic Era saw the emergence and diversification of several groups of marine reptiles, including ichthyosaurs, plesiosaurs, and mosasaurs.

Ichthyosaurs were dolphin-like reptiles that evolved during the Early Triassic period and went extinct during the Late Cretaceous period.

The Early Jurassic period saw the first long-necked marine reptiles, which went extinct at the end of the Cretaceous period.

At the end of the Mesozoic Era, the large marine reptiles known as mosasaurs went extinct.

4. Mammals

Life reconstruction of Vintana sertichi. Postcranial reconstruction is hypothetical. | Nobu Tamura via Wikipedia (CC BY-SA 4.0)

Although reptiles dominated the Mesozoic Era, the first mammals also evolved during this period.

Mammals first appeared during the Late Triassic period but remained small and relatively insignificant until the Cretaceous, when they began to diversify and fill ecological niches left vacant by the extinction of the dinosaurs.

Thus, from a small number of end-Cretaceous survivors, the modern mammalian fauna evolved and supplanted dinosaurs as the most common terrestrial animals.

5. Birds

Archaeopteryx birds dinosaurs flying among pine trees | Elenarts108 via Getty Images

Birds evolved from small theropod dinosaurs during the Jurassic period, and by the end of the Mesozoic Era, they had diversified into different species.

Birds are unique among reptiles because they are warm-blooded and have feathers for flight and insulation.

Separate from their dinosaurian ancestors, contemporary birds gained several adaptations, including flying feathers and colorful eggs.

Some of the most famous Mesozoic birds include Archaeopteryx and Confuciusornis.

Modern birds, or neornithes, first appeared in the Late Cretaceous.

They were the only species of birds to survive the mass extinction that occurred at the end of this period and later underwent diversification to become the numerous types we see today.

6. Plants

Cycads | Qin Ningzhen via Getty Images

The Mesozoic Era saw the emergence and diversification of several groups of plants, including gymnosperms and angiosperms.

Gymnosperms, which include conifers and cycads, dominated the Mesozoic Era and were the primary type of plant on land during this time.

Angiosperms, or flowering plants, first appeared during the Early Cretaceous period and quickly diversified to become the dominant type of plant by the end of the Mesozoic Era.

Extinction Events of the Mesozoic Era

Although the Mesozoic Era marked a time of great change and transformation in Earth’s history, it was also marked by several catastrophic events that resulted in the extinction of many species of plants and animals.

This era brought about three of the five mass extinctions that happened on Earth; the Permian-Triassic, Triassic-Jurassic, and Cretaceous-Paleogene extinctions.

The Permian-Triassic Extinction

Volcanic eruption with dinosaurs | NatuskaDPI via Getty Images

With an estimated 96% of all marine species and 70% of all terrestrial species perished, the Permian-Triassic extinction catastrophe, also known as the Great Dying, is one of the most disastrous periods in Earth’s history.

The evolution of biodiversity is thought to have been profoundly and permanently impacted by what is regarded as the most severe mass extinction event in the history of life on Earth.

The Permian-Triassic extinction catastrophe, which marked the end of the Permian and the start of the Triassic periods, took place roughly 252 million years ago.

Numerous theories have been put forth, but scientists are still debating the causes of the Permian-Triassic extinction event.

One of the most popular hypotheses holds that the event was brought on by gigantic volcanic eruptions in what is now Siberia, which released enormous quantities of carbon dioxide and other chemicals into the atmosphere and caused global warming and ocean acidification.

Permian–Triassic boundary at Frazer Beach in New South Wales, with the End Permian extinction event located just above the coal layer. | Dippiljemmy via Wikipedia (CC BY-SA 4.0)

Evidence for this theory includes the discovery of sizable igneous provinces in Siberia that are assumed to have originated during the same period and the existence of volcanic rocks and ash layers in the Permian-Triassic boundary.

Other hypothesized causes include impacts from asteroids, changing ocean circulation patterns, and variations in atmospheric oxygen concentrations.

The Permian-Triassic extinction event had long-lasting effects on the evolution of life on Earth.

It shaped the patterns of biodiversity today, with some groups of animals, such as mammals, evolving and diversifying in the aftermath of the extinction event.

The recovery of life after the Permian-Triassic extinction was a slow and gradual process that took millions of years.

It involved the evolution of new species to fill the ecological niches left vacant by the extinction, and the development of recent ecosystems and food webs.

The Triassic-Jurassic Extinction

Pangaea | Ianm35 via Getty Images

The Triassic-Jurassic extinction occurred approximately 201 million years ago at the boundary between the Triassic and Jurassic periods and was the second largest mass extinction in the Phanerozoic Eon, after the end-Permian extinction event, and led to the loss of approximately 20% of marine families and numerous terrestrial species. 

Although the Triassic-Jurassic Extinction Event’s causes are not entirely known, it is believed that several factors played a part.

One of the most popular hypotheses holds that the event was caused by a massive volcanic eruption known in what is now western Canada.

Pangaea’s disintegration, which affected ocean currents and the climate, was another significant cause.

Between the northern and southern landmasses, a new ocean basin called the Tethys formed as Pangaea split apart, altering ocean circulation patterns and eventually, the planet’s temperature.

The Triassic-Jurassic Extinction affected life on Earth, especially marine species.

On land, the extinction event had only a small influence; many plant and animal species continued to exist mostly unmodified.

There were, however, some noteworthy extinctions, such as the disappearance of several families of enormous reptiles, including the phytosaurs and aetosaurs, and the appearance of new dinosaur species.

The Cretaceous-Paleogene Extinction

Asteroid over Earth | Ignatiev via Getty Images

The Cretaceous-Paleogene extinction event, also known as the K-T extinction event, occurred approximately 66 million years ago and was the most recent and well-known extinction event of the Mesozoic Era.

It resulted in the extinction of the dinosaurs and many other forms of life, including marine reptiles, pterosaurs, and several groups of mammals. 

It is generally accepted that a huge asteroid that hit what is now Mexico and resulted in enormous volcanic eruptions, earthquakes, tsunamis, and wildfires, was the cause of the extinction catastrophe.

As a result of the impact, a dust cloud covered the planet, obstructing sunlight and resulting in global cold and catastrophic extinction.


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