How Dinosaurs

Went ExtinctBy Daniel He

Table of Contents

The Mesozoic Era 1

The Triassic Period 3

The Jurassic Period 4

The Cretaceous Period 5

The End of the Dinosaurs 6

Asteroid Impact 7

Volcanism 8

Ice Age 9

Climate Change 10

Competition with Other Species 11

Other Theories 12

The Mesozoic EraThe Age of Reptiles

The Mesozoic is an era that started at 252.2 million years ago to 65.5

million years ago, and is composed of the Triassic Period, the Jurassic Period,

and the Cretaceous Period.

The Mesozoic was a place of giants, with dinosaurs ruling the world. They

first evolved from Archosaurs into dinosaurs during the Triassic Period, turned

larger and more diverse in the Jurassic and Cretaceous periods, but got wiped

out by the K-Pg extinction and the end of the Cretaceous period.

But dinosaurs weren’t the only successful species in the Mesozoic, there

were pterosaurs roaming the sky, and pliosaurs ruled the seas (they also

evolved from archosaurs), and perhaps one of the only ones that no one

expected to survive, the first mammals also evolved during the Mesozoic, as

well as ichthyosaur (Triassic), turtles (late Triassic), flowering plants (Jurassic)

and birds (Cretaceous).

The most common dinosaurs of each period

There were some big changes to Earth during the Mesozoic. At the start of

the era, there were no seasons, and there was only one supercontinent,

Pangaea. Since most of that continent was far from water, the center of the

continent was mostly lifeless deserts that were hot enough to cook most

creatures alive. But the Earth was changing, and the gradual tilt of the Earth

created the seasons, and the continent also started to split up into their

formation today, and the scorching wasteland of Pangaea started to blossom

with life.

The Ancient Supercontinent of Pangaea, in the Jurassic, when all the landmasses were joined together

The Triassic PeriodDawn of a New Era

The Triassic started off as a hot, lifeless desert, having recently suffered

the Permian Extinction. Even the few survivors of the crisis were disappearing

quickly. But, as always, with death comes life, and when the old species dies,

the new takes over.

In the supercontinent of Pangaea, some of the species have survived, and

evolved. A new species, a two legged reptile called an Eoraptor, the first

dinosaur, diverged from archosaurs, and started to repopulate the Earth. They

evolved, diversified, and began to dominate the planet.

The planet started to go through changes, and the biggest change was

the splitting of Pangaea. Eventually the continents split far enough to house a

new sea, one that would become the northern Atlantic Ocean and the Gulf of

Mexico. With more water inland, there are more plants, with more plants

there are more herbivore dinosaurs, with more prey, there are more

carnivores. A new water source doesn’t only benefit fish and amphibians; it

helps land animals, too.

A scene from the Triassic

The Jurassic PeriodA Green World

The Earth during the Jurassic was truly a green world. There were Jungles

all across the two supercontinents Laurasia and Gondwana, as well as ferns

and conifers. Pangaea had split in half, with Laurasia to the north, and

Gondwana to the south.

The sauropods began to get huge, so more predators started to hunt in

groups. The predators also got larger, though, and they are starting to take the

shape that many large carnivore dinosaurs would take: short front leg, strong

back leg, large and powerful jaws, and their overall size increased as well.

An ocean predator, liopleurodon, evolved from archosaurs, and started to rule

the sea. The first mammals also appeared first in the Triassic. A couple million

years later, A new species evolved from the liopleurodon, the elasmosaurus,

and their skull got smaller, but their neck got longer as well, and they have a

total of 71 neck vertebrae. This gives them an advantage for that they can

attack a whole school of fish, and while their huge body stays invisible, their

neck rise up and can easily feed without much notice.

The Jurassic dinosaurs

The Cretaceous PeriodFinal Glory

The Cretaceous is the last period in the Mesozoic Era. The tyrannosaurus

rex, the triceratops, pachycephalosaurus, and spinosaurus (largest carnivorous

dinosaur of all times, 16 – 18 meters) all appeared during that period.

Flowering plants covered the planet, as well as many trees and ferns.

Other than the dinosaurs, the Earth was a place much like today, with most of

the continents near where they are today, and most of the plants seen today

other than deciduous trees. The mammals were also evolving into a shape

much like today’s rat with longer front leg. They lived in burrows to avoid

predators, although they would soon take over Earth, they were no match for

the dinosaurs.

But then something that not even enormous creatures like dinosaurs

could stop happened. The event killed 75% or more of all the species on Earth,

including all of the large reptiles, and most of the marine animals.

The Cretaceous Period

The End Of the DinosaursA Tragic Event

65.5 million years ago, in a catastrophic event called the K-Pg Extinction,

the dinosaurs were destroyed forever. This event ended the 185 million years

long rule of the dinosaurs, and the age of the reptiles. Scientists have always

been puzzled by how that happened, and these are some of the most popular

theories:

Asteroid Impact

Volcanism

Ice Age

Climate Change

Competition With Other Species

I’m also going to tell you about my theory and some other theories.

The extreme volcanism theory

Asteroid Impact

A lot of people believe that asteroids killed the dinosaurs. Because there has

been lots of evidence:

Molten rock:

Molten rock found all over the world at the Cretaceous – Paleogene boundary

indicates that a huge amount of energy suddenly melted and through these

rock very far away.

Craters:

There were craters all around the world, and a lot of them is believed to be

the one that was created by the K-Pg asteroid. But it was the discovery of the

crater in the Gulf of Mexico in 1978 that proves that the theory is very possible

Rare Metal:

A rare metal called iridium is found scattered around Earth at the K-Pg

boundary. Iridium is very rare in the Earth’s crust, but common on asteroids.

An artist’s impression of an asteroid impact scene

Volcanism

Volcanoes can also explain how the dinosaurs went extinct, but there was

also evidence of an asteroid impact, so that caused someone to think about a

combined theory: The Deccan Traps wiped out most dinosaurs, and the

asteroid cleaned up the rest.

The Deccan trays were formed by a flood basalt eruption about 66 million

years ago, and it could have made the air toxic.

Or it could have been the geographical movement that made other

volcanoes that did the job.

An example of a flood basalt eruption

Ice Age

Ice ages could also have killed the dinosaurs. There has been some fossils

to support this theory. Cold water planktons indicates that there was

something that suddenly made the water cold.

But an ice age does not explain evidence of the other things from that

time, so that cause a combined theory. Since an ice age small enough to not

leave much evidence probably couldn’t have killed the dinosaurs, it could have

been a volcano or an asteroid that helped with the job.

A small scale ice age

Climate Change

This is also a possible theory because there was definitely climate change

at that point, because there weren’t any seasons before. But tilting of the

Earth cause there to be seasons, and studies indicate that this happened

around the time dinosaurs went extinct.

A climate change event could have made a lot of species not used to the

new climate, and therefore it would explain why dinosaurs weren’t the only

ones that went extinct.

The four seasons

Competition with Other Animals

This is a plausible theory because scientists found that the dinosaur

population was already decreasing before the extinction. Although this might

not be the result of competition, it could have.

Mammals could have eaten the dinosaur’s eggs, spread disease, and a

number of things that all could have led to the extinction of the dinosaurs.

A mammal eating an egg, possibly a dinosaur’s

Other Theories

There are other theories for how the dinosaurs went extinct, but it’s very

unlikely that they are true:

Epidemics

A Planet Overrun By Males

Cosmic Rays

The Dinosaurs Just Faded Away Into Extinction

Dinosaurs Got So Big That They Crushed Themselves

Dinosaur Fart (containing methane) Killed Themselves

But don’t even think about believing in them. They are totally false.

Cosmic rays