The Earth’s history is split into various periods and chapters, all of which represent unique eras, happenings, and creatures.
One of the most famous of all these periods is the Jurassic Period, primarily for its diversity and the existence of dinosaurs.
The Jurassic period marked the end of the Triassic and predated the Cretaceous, all of which are different periods under the Mesozoic Era.
As the middle segment of the Mesozoic Era, the Jurassic period lasted approximately 201 to 145 million years ago, spanning over 56 million years and marking profound geological shifts, climatic changes, and the evolution of various species of both plants and animals.
This period was named after the Jura Mountains, a scenic range between France and Switzerland.
The term “Jurassic” was coined by the French geologist Alexandre Brongniart in 1829, who named it after the Jura Mountains to recognize the geological importance and the wealth of fossils in the region.
Geologists started classifying and defining the many eras of Earth’s history during Brongniart’s time based on the rock formations and the fossils they contained.
They discovered numerous Jurassic Period fossils from the Jura Mountains, including those of dinosaurs, marine reptiles, and prehistoric plants, when they examined the strata of sedimentary rocks there.
The entire timeline of the Jurassic period is notable in Earth’s history.
This article will focus on this timeline, highlighting as many noteworthy events as possible.
Keep reading as we embark on a captivating journey through the Jurassic Period, delving into the pivotal geological events and the remarkable evolutionary developments that defined this epoch.
Timeline of the Jurassic Period
As mentioned, the Jurassic period lasted 201 to 145 million years ago, and it is further divided into three separate timelines, which hold different happenings across the entire epoch.
1. The Early Jurassic
The beginning of the Jurassic period was labeled the “Early Jurassic,” which lasted from approximately 201.3 million years ago to 174.1 million years ago.
It followed the end-Triassic mass extinction event and marked the beginning of the age of dinosaurs.
During this time, the Earth experienced significant geological, climatic, and biological changes that shaped the course of evolution.
The beginning of this period was marked by the Hettangian age, named after Hettange-Grande in northeastern France.
The planet was still recovering from the mass extinction event at the end of the Triassic period, and land masses were beginning to separate, forming new continents.
One of the most significant happenings of this period was the evolution of a group of dinosaurs called theropods.
Other reptiles that evolved during this period include crocodylomorphs, turtles, plesiosaurs, and ichthyosaurs.
These reptiles dominated the seas, occupying ecological niches left vacant by extinct marine reptiles from the Triassic.
On land, dinosaurs diversified and spread across different areas, even while the Pangea supercontinent broke apart.
At the same time, the mammals that had appeared at the end of the Triassic period continued to evolve.
Earth’s climate during the Early Jurassic was typically warm and steady.
The dry habitats of the late Triassic gave way to increasingly humid and tropical ecosystems during this time.
Also, volcanic activity and tectonic movements continued to shape the Earth’s surface.
The breakup of Pangea led to the formation of the Central Atlantic Magmatic Province (CAMP), a massive volcanic province spanning modern-day eastern North America, Western Europe, and North Africa.
The eruptions associated with CAMP released vast amounts of lava and gases, potentially influencing climate and biodiversity.
2. The Middle Jurassic
The Middle Jurassic period is a crucial era in Earth’s history that spanned from approximately 174 million to 164 million years ago.
This period began immediately after the Early Jurassic period, and while parts of the Pangea supercontinent were still together, much of the landmass surrounded the equator.
The beginning of this period also gave way to a global increase in temperature, which led to the expansion of shallow seas across many regions, resulting in marine environments swarming with diverse organisms.
Dinosaurs continued to evolve during this period.
The Pangea supercontinent eventually broke into primary land masses, Laurasia to the north and Gondwana to the south.
While the dinosaurs had more opportunities to spread across different regions, the global temperature cooled, leading to the emergence of new species.
In terms of plant life, the Middle Jurassic witnessed the dominance of coniferous forests.
Cycads, ferns, and other primitive plant groups also thrived during this period.
3. The Late Jurassic
The Late Jurassic period, 163.5 million to 145 million years ago, began with the formation of the Atlantic Ocean caused by the separation of the Pangea supercontinent.
This era witnessed the appearance of newer continents and the evolution of dinosaurs like the Allosaurus and Stegosaurus.
The earth’s climate became drier and then came the appearance of species such as Diplodocus and Brachiosaurus.
Archaeopteryx, an early bird-like dinosaur, emerged as one of the first creatures capable of powered flight.
In the final stage of the Late Jurassic period, the climate became more unpredictable, marked by a mix of wet and dry periods.
As Pangaea continued to fragment, Laurasia and Gondwana began taking shape.
This era witnessed the rise of some of the most iconic dinosaurs, such as the mighty Tyrannosaurus rex, the horned Triceratops, and the swift Velociraptor.
The Late Jurassic period was also home to various plant life.
Conifers and ferns were dominant among terrestrial vegetation.
The first true flowers appeared during this period, marking a significant evolutionary development.
Major Organism Groups of the Jurassic Period
1. Dinosaurs
The Jurassic Period is renowned for its incredible diversity and abundance of dinosaurs.
These magnificent reptiles of different sizes, shapes, and lifestyles dominated terrestrial ecosystems.
They evolved into various sizes and ecological niches, adapting to different environments.
Three major groups of dinosaurs flourished: the theropods, sauropodomorphs, and ornithischians.
The theropods were bipedal carnivorous dinosaurs that included some of the most famous predators in history.
Species like Allosaurus and Ceratosaurus ruled the land with their sharp teeth and agile bodies.
Represented by enormous herbivorous dinosaurs, the sauropodomorphs were the largest creatures to have ever walked the Earth.
The Jurassic period saw the rise of massive sauropods like Brachiosaurus, Diplodocus, and Apatosaurus (formerly known as Brontosaurus).
The ornithischians were a diverse group of herbivorous dinosaurs that developed unique features such as beak-like jaws and elaborate armor or horns.
Stegosaurus and Triceratops, both famous representatives of this group, lived during the Late Jurassic.
2. Marine Reptiles
The oceans during the Jurassic Period were teeming with an impressive variety of marine reptiles.
This transition to marine life offered them an abundance of food sources and reduced competition compared to their terrestrial counterparts.
These reptiles mastered the art of swimming and developed various adaptations to thrive in the oceanic realm.
The ichthyosaurs were one of the most iconic groups of marine reptiles in the Jurassic Period, resembling modern-day dolphins in appearance, with long snouts, slender bodies, and powerful tails.
Another fascinating group of marine reptiles was the plesiosaurs.
These creatures had four flippers, a broad body, and an elongated neck, making them distinct from other marine reptiles.
3. Pterosaurs
A distinct group of flying reptiles known as pterosaurs evolved during the Jurassic period.
Pterosaurs were the first vertebrates to evolve powered flight, with their fossil record dating back to the Late Triassic period, approximately 228 million years ago.
They flourished during the Mesozoic Era and reached their peak diversity during the Jurassic.
Pterosaurs were incredibly diverse, ranging from the little insectivorous Dimorphodon to the enormous Quetzalcoatlus, which had a 40-foot-long wingspan.
Pterosaurs had an incredible anatomical design that was optimized for flying.
In contrast to birds and bats, pterosaurs possessed wing structures that were supported by an extended fourth finger that served as the main wing bone, or pteroid.
The patagium, a thin membrane made of skin, muscle, and other components, formed their wings and extended from the long fourth finger to the ankle.
4. Invertebrates
The Jurassic Period witnessed the dominance of various invertebrate groups.
Ammonites, spiral-shelled marine mollusks, were particularly abundant and diverse.
With their distinctive spiral-shaped shells, ammonites were cephalopods closely related to modern-day squids and nautiluses.
They displayed a remarkable variety of shapes, sizes, and ornamentations, making them valuable index fossils for dating rock layers.
Another popular invertebrate in this period was Belemnites. Unlike ammonites, they possessed internal shells instead of external ones.
These bullet-shaped structures, composed of calcium carbonate, played a crucial role in buoyancy control.
Belemnites were fast-swimming predators, preying on small fish and crustaceans.
Other invertebrates include crinoids, brachiopods, corals, etc.
5. Plants
The Jurassic Period saw the proliferation of various plant groups.
The environments provided fertile grounds for an astonishing diversity of plant life.
Conifers, cycads, and ferns were prevalent, covering vast expanses of land.
Gymnosperms, plants that produce seeds without enclosing them in fruits, were the dominant flora during the Jurassic.
They played a crucial role in shaping the terrestrial ecosystems of the time.
Plants like the Equisetum towered over other vegetation, while tree ferns provided habitats for numerous creatures.
Cycads were also among the dominant plants in this period.
Commonly referred to as “living fossils,” these gymnosperms were characterized by their palm-like appearance and large, compound leaves.
Cycads exhibited remarkable resilience, adapting to both arid and humid conditions.
Their presence was crucial in establishing habitats for diverse herbivorous and insect species.
Conifers, another group of gymnosperms, flourished during the Jurassic Period.
Towering trees with needle-like leaves, conifers were well-suited to various climates and formed extensive forests.
Other plants from this period include ferns, Bennettitales, etc.
These diverse plant communities formed the basis of terrestrial ecosystems and provided food and shelter for many Jurassic organisms.
Plants in the Jurassic period developed various adaptations to cope with environmental challenges.
Gymnosperms have developed strong bark to survive wildfires, while others have grown deep roots to get water and nutrients.
In addition, the evolution of intricate reproductive organs and pollination processes promoted the emergence of new plant species and ecological interactions.
Fossils and Their Significance in Understanding the Jurassic Period
Like the fossils of other periods under the Mesozoic Era, the fossils of animals from the Jurassic period are found in many parts of the world.
The most popular animals from this period are dinosaurs, and the fossils of these giant reptiles give experts more information about their anatomy, behavior, and ecological interactions.
These fossils also help these experts reconstruct ancient ecosystems and explore the intricate dynamics of predator-prey relationships during this time.
Furthermore, fossils of marine reptiles like ichthyosaurs and plesiosaurs provide a look into the wide variety of species that formerly roamed the waters.
The classic ammonites are coiled-shelled cephalopods that serve as accurate dating tools for rocks and stratigraphic correlations, in addition to providing important information on the ecology and evolution of these creatures.
One of the most important evolutionary events of the Jurassic period was the rise of flowering plants, known as angiosperms, and the fossils of these pollen grains and plant fragments provide crucial evidence for tracking the emergence and diversification of these plants.
Scientists can reconstruct former habitats and climates by analyzing fossils from the Jurassic period.
Fossil plant assemblages also provide insights into past ecosystems.
For animals, the isotopic makeup of preserved teeth and bones reveals information on the food, migratory habits, and even water supplies of long-extinct species.
In addition to their biological importance, Jurassic fossils are essential for stratigraphic research and linking geological formations.
Geologists use these fossil assemblages found in different rock strata as distinguishing identifiers to date and determine the relative ages of different rock formations worldwide.
Extinction Events of the Jurassic Period
The Pliensbachian-Toarcian Extinction
The Jurassic period began after one of the most significant extinction events in the Triassic period, the Late Triassic Extinction, which led to the demise of many dominant species.
Around 183 million years ago, during the Early Jurassic period, the Pliensbachian-Toarcian extinction event occurred, affecting marine ecosystems.
It is characterized by the widespread disappearance of marine organisms, including ammonites, bivalves, brachiopods, and marine reptiles.
This event stands out as one of the most severe marine extinctions in Earth’s history, second only to the end-Permian mass extinction.
Scientists have proposed multiple causes and triggers for the Pliensbachian-Toarcian extinction event, but no definitive consensus has been reached.
Some leading theories include fluctuations in global climates, such as rising sea temperatures and changes in oceanic circulation patterns, oxygen depletion in the ocean, changes in ocean chemistry, tectonic activity, etc.
The Early Jurassic Terrestrial Extinctions (The End-Triassic Event)
A catastrophic extinction called the End-Triassic event, which took place around 201 million years ago, came before the Early Jurassic terrestrial extinctions.
Although this incident mostly occurred in the Triassic Period before it, its impacts on terrestrial ecosystems persisted until the Early Jurassic.
It signaled the demise of numerous prominent groups, including some archosaurs and big amphibians, opening up ecological niches for new species to appear.
The decrease and eventual loss of numerous synapsids was one noteworthy repercussion of the Early Jurassic terrestrial extinctions.
Dicynodonts and traversodonts were two of the many types of reptiles that belonged to the group of synapsids.
These herbivorous and carnivorous animals contributed significantly to the development of terrestrial ecosystems throughout the Late Triassic, but their numbers sharply decreased during the Early Jurassic.
Multiple factors likely contributed to the Early Jurassic terrestrial extinctions, including environmental changes during this period.
The breakup of the supercontinent Pangaea led to the formation of new landmasses, altering climatic patterns and causing shifts in ecosystems.
Changes in temperature, humidity, and the availability of resources could have disrupted the delicate balance of species and triggered extinctions.
Also, the rise of new groups of organisms during the Early Jurassic may have played a role in the terrestrial extinctions.
As the archosaurs and dinosaurs began to diversify and dominate, competition for resources intensified.
This increased competition, combined with changes in habitats and ecological imbalances, could have contributed to the decline and eventual extinction of less competitive species.
The Late Jurassic Extinction Event
Marine life was predominantly impacted by the Late Jurassic extinction event, with several species declining and disappearing.
Together with ammonites, belemnites, and certain bivalves, marine reptiles like ichthyosaurs and plesiosaurs were among those most severely affected.
The exact causes of the Late Jurassic extinction event remain a topic of ongoing scientific investigation.
Several hypotheses have been proposed, taking into account various environmental factors that may have played a role.
Some of the leading theories include fluctuations in sea levels due to tectonic activity, changes in global climate that may have altered marine habitats, variations in temperature and precipitation patterns, volcanic activity, etc.
The extinction catastrophe that occurred in the Late Jurassic had a significant impact on how life on Earth later developed.
It created ecological conditions that allowed new species to flourish in the developing ecosystems of the Late Jurassic and Early Cretaceous.
For example, the extinction of marine reptiles prepared the way for the diversity and subsequent domination of marine fish, sharks, and rays.
Sources:
- https://ucmp.berkeley.edu/mesozoic/jurassic/jurassic.php
- https://www.nps.gov/articles/000/jurassic-period.htm
- https://www.livescience.com/28739-jurassic-period.html
- https://scienceviews.com/dinosaurs/jurassic.html
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