The Mesozoic Era, a term meaning middle life, covers 252 to 66 millions of years ago (Mya). This dinosaur era is divided into the Triassic, Jurassic, and Cretaceous periods.

PROLOGUE: THE GREAT DYING

Pangaea Supercontinent

Since 336 Mya, land on the earth has been one c-shaped supercontinent near the equator. It is named Pangaea, which means All Earth. It is surrounded by a single ocean called Panthalassa, meaning All Sea.   

Pangaea Super-desert

Having limited coastlines, much of  Pangaea is dry and humid. There a massive desert in the center of the supercontinent. Having a constant temperature about 50c, the super desert in mostly uninhabited.

Great Permian Extinction

252 Mya: Due to one or more catastrophic events, such as a massive meteor impact and/or volcanic eruption, an estimated 95% of life on earth is wiped out. The 47 million years long Permian era comes to an end.

Siberian Volcanic Event

 Massive volcanic eruptions occur in Siberia. It continues for two million years and creates a volcanic rock region known as the Siberian Traps. The ash spewed from the event may be one cause behind the great extinction.

The Great Permian Extinction is the worst extinction event in earth’s history. It is sometimes known as The Great Dying.

TRIASSIC PERIOD: 252-200 Mya

Ocean Changes

Due to underwater volcanic activity during the great extinction, the ocean may experience lower oxygen levels and higher water acidity. This wipes out much marine life and forces surviving creatures to adapt.

Ancient Tethys Ocean

250 Mya: There is a gradual rise in sea-levels. Isolated marine communities are soon brought together and adapt even further.  Pangaea begins to rupture and a new ocean begins to form within the c-shaped supercontinent.

Fish Flipper Lizards

Some land-based lizards return to the sea and become an aquatic species. They swim in an eel-like manner by moving their entire body side to side. They are known as Ichthyopterygia, which means fish flippers.

Complete-Bone Fishes

Ray-finned fishes emerge with a mouth to tail bone structure. They develop the ability to protrude their jaws outwards which allows them to grab and feed on prey. Teleosts is derived from Greek and means Complete Bone.

Complete-bone fishes now make up over 80% of all living fish.

Age of Reptiles

It takes over four million years for life to fully recover and diversify after the great extinction. Reptiles, requiring less water to survive, become the most prominent animals across the earth.

Archosaurs

Archosaurs are the main group of reptiles to emerge. They have stronger limbs, which allows for improved movement and breathing. Their name means ruling reptiles.     

Crocodilian-Line Archosaurs

A branch of archosaurs emerges with large skulls and narrow elongated snouts. Ancestors to crocodiles and alligators, they are initially an extremely diverse group that live in various different habitats.

Crocodilian-Line Dominance

Crocodilian-line archosaurs become the most common reptiles. Giant four-legged members of the group gradually emerge and become the top predators of the Triassic period.

Archosaurs are the ancestor of the dinosaurs, pterosaurs, and crocodiles. 

Age of Conifers

Not requiring much water, cone-bearing trees and shrubs are the dominant land plants in Pangea. These include redwood, pine, and cypress trees. Conifer is a Latin word meaning one that bears a cone.

The First Grasshoppers

250 Mya: Leaping and plant-chewing insects emerge. They feature camouflage and their jumping ability serves to both startle and escape from predators. They occasionally gather in locust swarms.

Bird-Line Archosaurs

249 Mya: A branch of archosaurs emerge with single-hinged ankles, which allow for better mobility. Some gradually evolve feathers and the ability to fly. The group includes dinosaurs and pterosaurs.

Asilisaurus

245 Mya: A thin four-legged archosaur reptile emerges with a long neck, long tail, and erect legs. It is the earliest ancestor of the dinosaurs and pterosaurs. Its name means Ancestor Lizard.

The ancient Greek word for reptile is Saurus. Many lizards from this era have the term integrated into their name, but not all are in the dinosaur line

Stony Corals

Corals that build hard skeletons emerge. Although some species are solitary, most colonize and create hard coral reefs in shallow tropical waters. They are known as Scleractinia, which means hard-ray.

Ichthyosaurs

Fish flipper lizards that returned to the sea evolve. The dolphin-shaped reptiles are called Ichthyosaurs, which means Fish Lizards. Some grow to be over sixteen metres in length.

Flipper Reptiles

245 Mya: An aquatic lizard emerges with strong flippers. The meat-eater has a long neck to swiftly grab prey and to stick its head above the water to breath. They are known as Sauropterygia, which means lizard flippers.

Turtle Ancestor

240 Mya: A reptile emerges having a bulky body with thick rib-like bones that are partially fused together. It is named Pappochelys, which means grandfather turtle. It is likely the ancestor of all turtles.

Large marine lizards of this era are often grouped with dinosaurs, but they reside on their own branch of reptile. Flipper Reptiles and the Turtle Ancestor belong to the same group of aquatic lizards.  

The First Dinosaurs

233 Mya: Instead of wide sprawling limbs, some archosaurs evolve stronger and longer erect limbs beneath their body. The reptile branch is called Dinosaurs, which means Great Lizard in Ancient Greek.

South American Origin

The first dinosaurs emerge in southwestern Pangea, which will become South America. They scavenge after food and gradually expand throughout the interconnected supercontinent.

Lizard-Hipped Dinosaurs

The first great lizards belong to the Saurischia dinosaur order, which means lizard-hipped. Initially omnivorous, they soon split into two major branches: the plant-eating sauropods and the meat-eating theropods.

Sauropod Ancestors

231 Mya: Plant-eating dinosaurs emerge with long necks that allow them to reach higher plants. Initially small and two-legged, they gradually evolve into massive four-legged dinosaurs.

The first dinosaurs likely emerged sometime between 243 and 233 million years ago.

Theropod Dinosaurs

231 Mya: Two-legged meat-eating dinosaurs emerge that have clawed feet and small arms. This allows them to catch and grasp prey. They become known as the theropod sub-order of dinosaurs, which is Greek for beast-feet.

Herrerasaurus Dinosaur

A pony-sized theropod dinosaur emerges. It is a swift runner that can easily catch prey. One of the earliest theropods, it is named Herrera’s Lizard after the rancher who discovered its first fossils.  

Eoraptor Dinosaur

A cat-sized theropod dinosaur emerges. It may have been omnivorous and feed on plants. Being one of the earliest-known true dinosaurs, Eoraptor’s name means dawn plunderer.

Eodromaeus Dinosaur

A small and swift meat-eating dinosaur emerges. Initially classified as a species of Eoraptor, it determined to be its own group of theropods and is named Eodromaeus, which means dawn runner.

Only the theropod dinosaurs are meat-eating carnivores, most dinosaurs are plant-eating herbivores.

Winged Lizards

228 Mya: Some archosaurs develops the ability to glide and then fly. The branch of reptiles becomes known as Pterosaurs, which is Greek for Winged Lizard. The first large animals to develop the ability to fly.

Crocodile-Ancestor

225 Mya: The earliest form of crocodiles emerge in the crocodilian-line of archosaurs. The small land-based reptiles are known as Crocodylomorpha, which means crocodile-shaped.

Dog-Teeth Animals

Since 256 Mya, a mammal-like species has been evolving a jaw formation which allows for simultaneous chewing and breathing. The rat-like animals are called cynodont, which means dog-teeth.

The First Mammals

225 Mya: Diverging from dog-teeth animals, the first mammals emerge. They have mammary glands that allow females to produce milk for their babies. They still lay eggs, but also develop fur.

While often categorized as a dinosaur, pterosaurs are a distinct branch of reptile. They are popularly known as pterodactyls. However, pterodactyl is a type of pterosaur that doesn’t emerge until 150 Mya.  

First Turtles

220 Mya: Lizards emerge with a bony shell to protect their bodies. The earliest known turtle is named Odontochelys Semitestacea, which means Toothed Turtle with a Half-Shell.

Hollow-Boned Dinosaur

A slender long-necked theropod dinosaur emerges. Growing up to 3 meters and weighing less than 100 pounds, the hollow-boned Coelophysis is a fast and agile hunter. Its name means hollow form.

Pangea Rifting

215 Mya: The outer shell of the earth is divided into seven or eight major tectonic plates. The plates begin to move apart, which spawns earthquakes, volcanoes, fissures, and new mountains throughout Pangea.

Triassic Rock Layers

The rifting of Pangea contributes to the creation of three distinct layers of rock: reddish-coloured desert rocks, the sea-based limestone, and the organic-rich black slate. It provides the name for the period.

There are many Coelophysis fossils, which caused it to become one of the earliest discovered dinosaurs.

Mesozoic Marine Revolution

Sea creatures that live on the seabed begin to develop shell-crushing and boring features. This allows them to eat the abundant shellfish. These animals include the ancestors of starfish, crabs, and molluscs.

Sauropod Dinosaurs

210 Mya: Large sauropod dinosaurs emerge with very long necks and long tails. It has four pillar-like legs to support its size and weight. Due to their blunt flat feet, their Greek name means lizard-feet.

Central Atlantic Magmatic Province

The rifting of Pangea triggers 600,000 years of massive volcanic activity. It creates a vast 11 million km2 area of cooled magma in what will become the Atlantic Ocean. It is the largest magmatic region on the earth.   

Triassic–Jurassic Extinction Event

201 Mya: The widespread volcanic activity releases massive amounts of carbon monoxide. This raises the earth’s average temperature and acidifies the oceans. Over 75% of life goes extinct.

The Triassic-Jurassic Extinction Event is the fourth largest extinction event in history. There is a debate about the cause or causes of the extinction, though volcanic activity is likely one major factor.

JURASSIC PERIOD: 201-145 Mya 

Crocodilian-Extinction

Most archosaurs in the crocodilian-line go extinct. Only the land-based crocodylomorpha line survives the extinction. The crocodile-form reptiles gradually diversify and fill some newly opened habitats.

Dinosaur Dominance

With many habitats emptied in the extinction event, the great lizards fill the gaps. With the death of most crocodilians, dinosaurs become the dominant animals throughout Pangea.  

Ornithischia Dinosaurs

200 Mya: A second order of dinosaurs emerge. The plant-eating reptiles live in herds and some also feature hair or feather-like pelts. The major group is known as Ornithischia, which means bird-hipped.  

Armored Dinosaurs

199 Mya: Some Ornithischian dinosaurs begin to develop body armour and spikes for protection from predators. They become known as the thyreophora suborder of dinosaurs, which means shield bearer in Greek.

It is traditionally believed that ornithischia dinosaurs emerged from their own unique line of archosaurs. However, some now argue that ornithischias are a close relative of theropods and sauropods belong on their own unique line.

Ammonites

Spiral-shelled squid-like creatures known as ammonites almost die out in the extinction event. However, they recover and proliferate with even more complex and diverse shells.

Ichthyosaurus 

Ichthyosaurus emerges as the most common-type of the dolphin-shaped fish lizards. Although a smaller Ichthyosaurs, its high swimming speed can allow it to escape predators. It becomes one of the last fish lizards.

Marine Crocodiles

Some of the land-based crocodile-shaped reptiles transition to the sea and become semi-aquatic. One group, known as the Thalattosuchia, becomes fully aquatic.

Plesiosaurs

190 Mya: The extinction event wipes out the aquatic long-necked flipper lizards except for the Pliosaur line. The meat-eating reptile feeds on Ichthyosaurs and other marine life. Pliosaur is a name meaning More Lizard.

Some of the earliest discovered fossils belong to the Plesiosaur. Descriptions of the legendary Loch Ness Monster is reminiscent of a Plesiosaur.

Jura Mountain Range

Pangea rifting, volcanic activity, and the extinction of shell-based marine life creates distinct rock and fossil layers. It gradually creates a fossil-rich three-layer limestone mountain range in Laurasia.

Pangea Split

The Pangaea supercontinent begins to split into two separate landmasses:  Laurasia drifts northward and Gondwanaland drifts southward. The North Atlantic Ocean emerges, though remains a narrow channel.

Humid Rainforests

Pangea’s breaking creates more coastlines and humid climates, the arid deserts are gradually replaced by extensive rainforests. Dinosaur spread into the expanding forests.

Flowering Plants

180 Mya: Plants emerge with a robust enclosed seed known as an angiosperm. The fast-growing and adaptable plants begin to spread. They provide nutritious food to plant-eating dinosaurs and insects.

The Jurassic Period is named after the Jura Mountains in the European Alps. Geographer and naturalist Alexander von Humboldt first detected the unique geological era during a tour of the mountains in 1795.

Bird-Like Dinosaurs

A branch of theropod dinosaurs goes through a process of rapid miniaturization. The tiny dinosaurs feature winged forelimbs, curved serrated teeth, and sickle-clawed feet. Their Greek name, Paraves, means Near-Birds.

Climbing-Wing Dinosaurs

A family of bird-like dinosaurs evolve the ability to climb trees. They likely live in the trees and may have the ability to glide. They are called Scansoriopterygidae, which means Climbing-Wing.

Bird-Wing Dinosaurs

165 Mya: Some bird-like dinosaurs evolve in eastern Laurasia with the ability to glide or fly. They retain the long bony tails of their ancestors. They are known as Avialae, which means Bird-Wings.

Feathered Dinosaurs

Some theropod dinosaurs begin to develop colourful feathers. They are initially used to attract a mate, but they gradually become an aid for insulation and flight.

Feathers do not preserve well, but there is increasing fossil evidence to suggest that dinosaurs may have always had some degree of feathering. However, some dinosaurs may have shed those feathers in adulthood.

Tyrant Lizards

165 Mya: A branch of theropod dinosaurs emerge with an increasingly larger skull and blunt snout. Initially small, they gradually grow in size. They are known as Tyrannosauroidea, which means Tyrant Lizard Forms.

Grazing Dinosaurs

163 Mya: Small two-legged Ornithischia dinosaurs emerge. Similar to cattle, they evolve the ability to graze and chew their food. Due to their bird-like feet, their Greek name of Ornithopoda means bird-feet.

Archipelago of Europe

The breaking of Pangea increases sea levels in certain regions. In Laurasia, the region that will become Europe is located closer to the equator. It is covered in a shallow warm tropical sea and has about twelve large islands.

Salamanders

160 Mya: Tiny lizard-like amphibians emerge that have blunt snouts, four legs, moist skin, and evolve the ability to regenerate lost limbs. Frequently noticed hiding in firewood, their Greek name means Fire Lizard.

Horned-Face Dinosaurs

161 Mya: Ornithischian dinosaurs emerge in Laurasia with facial horns and frilled necks. Initially small and two-legged, some evolve into massive four-legged dinosaurs. They are known as Ceratopsia, which means horned-faces.

Stegosaurus

155 Mya: An armoured plant-eating dinosaur emerges in Laurasia that has tail spikes and vertical plates along its back for defence. Their Greek name means Roof Lizard.

Allosaurus

155 Mya: A large theropod dinosaur emerges with a large skull and heavy tail. A dominant predator for five million years, they are known to hunt stegosaurus. Allosaurus means Different Lizard.

Bird Ancestors

150 Mya: Raven-sized feathered dinosaurs emerge. Belonging to the avialae branch, they are the earliest ancestor to birds. The best-known is called Archaeopteryx, which means Ancient Feather.  

One of the most complete Allosaurus was discovered in the United-States and given the nickname of Big Al.  

Brachiosaurus

154 Mya: A large dinosaur sauropod emerges in North America that features an inclined torso and shorter tail. Its Greek name means Arm Lizard due to its oddly long front limbs which causes its inclined body.  

Diplodocus

One of the longest sauropod dinosaurs emerge. They can whip their tails and produce a canon-like boom to intimidate predators. It is known as a double-beam dinosaur for its strong boned tail.

Giraffatitan

150 Mya: A very tall and heavy sauropod dinosaur emerges in Africa. Due to its giraffe-like build, the sauropod dinosaur is given the name Titanic Giraffe. It is the largest dinosaur of the time.

Jurassic-Cretaceous Boundary

145 Mya: Many large dinosaurs and marine reptiles slowly die out. The exact cause remains unknown, though some speculate it to be a gradual change in plant life.

Most cultural depictions of Brachiosaurus are actually closer to the Giraffatitan (including the film Jurassic Park).

CRETACEOUS PERIOD: 145-65 Mya

Warm Climate

There is a brief cold period which brings glaciation in northern regions, but it is soon replaced by a long warming period. There are higher water levels, which causes many shallow inland seas to appear.

Cretaceous Layers

That warm shallow seas provide extensive habits for marine creatures to thrive. Some marine organisms shed their shells, which creates chalk layers in many regions. The Latin word Cretaceous means Chalky.

Gondwanaland Split

Having split from Pangaea, the minor supercontinent Gondwanaland begins to split further. The continents of Africa, South America, South Asia, Antarctica, and Australia gradually emerge.

South Atlantic

North America begins to move northward. With western Gondwanaland splitting into South America and Africa, the southern half of the Atlantic ocean emerges in between the two new continents.

Pangaea is the last of an estimated eleven supercontinents throughout history. Another supercontinent will likely form in the next 100-200 million years.

Triconodonts

A cat-sized meat-eating mammal emerges with long canines and a powerful jaw. It likely preys on smaller mammals and dinosaurs. It name means Three Coned Tooth.

Titan Dinosaurs

145 Mya: With reduced competition from the recent extinction, even larger and heavier dinosaurs emerge. The largest known land animals, the sauropods are named after the mythological Greek Titans.

Raptors

143 Mya: Some of the bird-like paravian dinosaurs grow larger in size. The fast running dinosaur has feathers, wing-like arms, talons, and binocular vision. Some may have developed the ability to glide.

The First Ants

140 Mya: An insect emerges with elbowed antennae and a node-like body with a narrow waist. They form colonies and feed off flowering plants. The word ant is of Germanic origin and means the biter.

Raptor’s true name is Dromaeosauridae, which means running lizards. Due to the popular velociraptor, the entire dinosaur family is often informally known as raptors. They are much smaller than portrayed in such films as Jurassic Park. 

Utahraptor

126 Mya: The largest member of the raptor family emerges. Measuring up to seven meters long, the Dromaeosauridae dinosaur was first discovered in Utah and was subsequently named after the U.S. state.

Feathered Tyrant

124 Mya: A tyrant dinosaur emerges with feathers in eastern Laurasia, which will become China. It is the largest known dinosaur with feathers and it is named Yutyrannus, which means Feathered Tyrant.

The First Birds

121 Mya: A branch of tiny winged theropod dinosaurs evolve stronger rib cages and shoulders. This allows them to flap their wings and sustain powered flight. The first true birds emerge.     

Microraptor

120 Mya: A crow-sized raptor emerges that features four wings and the possible ability to fly. The paravian dinosaur is one of the common types of raptor. Its name literally means small one who seizes.

Flowering Plants

Flowering plants, having a robust enclosed seed known as an angiosperm, gradually become the dominant plant-type. However, Stegosaurus do not eat flowering plants and slowly dwindle to extinction.

Platypus Ancestor

115 Mya: The ancestor of the platypus emerge in southern Gondwanaland. They swim between the slowly separating continents of Australia, Antarctica, and South America.

Spinosaurus

112 Mya: A dinosaur emerges in North Africa with long spines on its back. One of the largest meat-eating dinosaurs, it hunts for food on land and in water similar to its distant reptile cousin the crocodile.

First Bees

100 Mya: With flowering plants replacing conifer trees, it likely contributes to the emergence of a flying insect that feeds on pollen. The early bees are closely related to wasps and ants.

Eighty-percent of plant life today is in the angiosperm family. Honey-producing bees do not appear until around 34 mya.

Gondwanaland Split

The minor supercontinent Gondwanaland continues to drift south. A split creates the continent of Africa and the subcontinent of India. The Indian Ocean begins to emerge around India.

Rising Sea Levels

The continued shifting and splitting of continents creates many underwater deposits and causes water levels to increase. The seas reach their highest point of the era and many regions are flooded.  

North American Inland Sea

100 Mya: A wide but shallow inland sea floods the central region of North America. Known as the Western Interior Seaway, it splits the continent in two. Many large marine creatures come to reside in the seaway.

The First Ticks

Miniature arachnids emerge that feed on the blood of warm-blooded animals. They have eight legs and their pear-shaped body swell with blood when feeding.

Gondwanaland is named after the Gondwana region in Central India.

Giganotosaurus

A massive theropod dinosaur emerges in South America. It likely works in a group to take down large plant-eating dinosaurs. One of the largest-known theropod dinosaurs, its name means Giant Southern Lizard.

Argentinosaurus

97 Mya: A titan dinosaur emerges that is over 30 metres long; one of the longest and largest known dinosaurs. Discovered in Argentine, the South American dinosaur’s name means Argentine Lizard.

Crocodilia

95 Mya: The earliest ancestor of the crocodile and alligator emerges. Due to their prevalence in the Nile river, the word crocodile is derived from Greek and means “Nile Lizard”.  

First Snakes

94 Mya: Evolving from burrowing reptiles, a legless and elongated lizard emerges. The name Snake is derived from the early Indo-European word that means to crawl or to creep.

Campanian Explosion

83 Mya: The continuing warm climate causes sea levels to rise and cover many coastal regions. This climate may have favoured the dinosaurs, which allowed them to flourish and diversify.

Tyrant Dominance

81 Mya: The largest tyrant lizards emerge and become the dominant predators in North America and Asia. They have tiny simple arms and their long legs allow for fast movement.

Rocky Mountain Growth

Continental shifting initiates a long period of mountain building in western North America. The Rocky Mountains, some of which already exists in southern regions, begins to emerge in northern regions.

Velociraptor

75 Mya: A fast and feathered bird-like dinosaur emerges. The turkey-sized reptile features a long tail and sickle-shaped claws which allows the raptor to tackle its prey. Its Latin name means swift seizer.

Ironically, most of the dinosaurs featured in the Jurassic Park films are actually from the Cretaceous Period.

North America Reformed

70 Mya: A colder climate gradually reduces the size of the Western Interior Seaway and North America soon returns to a single continent. The sea’s withdrawal creates a fossil-rich region known as Hell Creek Formation.

The Largest Pterosaur

The largest of the pterosaurs emerge in North America. It has a wingspan of over 10 meters but may have only weighed 90 kilograms. It is named Quetzalcoatlus after the Mesoamerican serpent god.

Tyrannosaurus Rex

68 Mya: The largest of the tyrant dinosaurs emerge in North America. Tyrannosaurus Rex measures over 12 meters long and weighs up to 14 tons. Its name means King of the Tyrant Lizards.

Triceratops

A dinosaur with three horns emerges in North America. Its horns provide protection against predators such as the tyrannosaurus and raptors. Triceratops is a Greek word that means three-horned face.

Triceratops is one of the last dinosaurs to emerge. So far, over 700 dinosaurs species have been identified and named.   

Chicxulub Meteor Impact

66 Mya: A meteor up to 15 km wide hits the southern tip of North America. It creates the 180 km wide crater and a worldwide dust cloud that blocks out sunlight. It may have also increased volcanic activity.

Cretaceous-Paleogene Extinction Event

The meteorite and the subsequent dust cloud initiates drastic and immediate climate change throughout the earth. Most animals over 25 kg die. An estimated 75% of life goes extinct, many within hours.

Ruling Reptile Extinction

Most archosaurs are wiped out, this includes their descendants the dinosaurs, pterosaurs, and large aquatic lizards. However, a few smaller species may survive for another two million years.

Ruling Reptile Descendants

With the ability to fly to better climates, birds become the only surviving descendants of the dinosaurs. Crocodilia become the only surviving reptiles from the archosaur line.

Cretaceous–Paleogene event is the only known major extinction caused by a meteor impact. A few scientists argue for alternate or additional causes. These include volcanic activity, multiple impacts, and/or rapid sea level change.

END OF AN ERA

The Cretaceous-Paleogene Extinction Event marks the end of the dinosaur age, the Cretaceous period, and the Mesozoic era. This is also the beginning of the Cenozoic era, which is also known as the Age of Mammals.