Mesozoic Era - The Age of
Dinosaurs
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
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Printed: December 22, 2015
AUTHORS
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
www.ck12.org
C HAPTER
Chapter 1. Mesozoic Era - The Age of Dinosaurs
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Mesozoic Era - The Age of
Dinosaurs
• Summarize life during the three periods of the Mesozoic Era.
• Explain why the Mesozoic Era is called the age of the dinosaurs.
• Explain what happened to the dinosaurs.
What exactly is a dinosaur?
Two dinosaurs wade through shallow waters to get to the vegetation on this island. The Mesozoic Era is the age
of dinosaurs. These animals grew so large they dominated the planet. Dinosaurs were so dominant that it took a
catastrophic, environment-changing event for mammals to be able to take over.
Mesozoic Era: The Age of Dinosaurs
The Mesozoic Era is literally the era of “middle life.” It is also known as the age of dinosaurs. It lasted from 245
to 65 million years ago and is divided into the three periods described in Figure 1.1. The Mesozoic began with the
supercontinent Pangaea. Then, during the era, Pangaea broke up and the continents drifted apart. The movement of
continents changed climates. It also caused tremendous volcanic activity.
Mass extinctions occurred at the end of the Triassic and Cretaceous Periods. The first extinction paved the way for
a dinosaur takeover. In the second extinction, the dinosaurs finally disappeared. At the link below, you can watch
a video about these and other exciting events during the age of dinosaurs. http://www.youtube.com/watch?v=watgb
11LOHE
The Triassic Period: During the Triassic Period (245–200 million years ago), the first dinosaurs branched off from
the reptiles and colonized the land, air, and water. Huge seed ferns and conifers dominated the forests, and modern
corals, fish, and insects evolved. The supercontinent Pangaea started to separate into Laurasia (today’s Northern
Hemisphere continents) and Gondwanaland (today’s Southern Hemisphere continents). The Triassic Period ended
with a mass extinction.
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FIGURE 1.1
The Mesozoic Era consists of the three periods described here.
The Jurassic Period: The next period, the Jurassic Period (200–145 million years ago), began after the mass
extinction that ended the Triassic Period. This mass extinction allowed dinosaurs to flourish in the Jurassic Period.
This was the golden age of dinosaurs. Also during the Jurassic, the earliest birds evolved from reptile ancestors, and
all the major groups of mammals evolved, though individual mammals were still small in size. Flowering plants
appeared for the first time, and new insects also evolved to pollinate the flowers. The continents continued to move
apart, and volcanic activity was especially intense. The classic Steven Spielberg movie Jurassic Park realistically
depicts some of the dinosaurs present during this period: http://www.youtube.com/watch?v=Bim7RtKXv90 .
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Chapter 1. Mesozoic Era - The Age of Dinosaurs
MEDIA
Click image to the left or use the URL below.
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The Cretaceous Period: During the Cretaceous Period (145–65 million years ago), dinosaurs reached their peak in
size and distribution. Tyrannosaurus Rex, weighed at least 7 tons. By the end of the Cretaceous, the continents were
close to their present locations. Earth’s overall climate was warm; even the poles lacked ice. The period ended with
the dramatic extinction of the dinosaurs.
What happened to the dinosaurs? Why did they go extinct at the end of the Cretaceous Period? Some scientists
think a comet or asteroid may have collided with Earth, causing skies to darken, photosynthesis to shut down, and
climates to change. A collision was probably at least a contributing factor. Without the dinosaurs, there were many
opportunities for new organisms to exploit in the next era, the Cenozoic. Which living things do you think took over
where the dinosaurs left off?
Summary
• The Mesozoic Era is the age of dinosaurs. They evolved from earlier reptiles to fill niches on land, in the
water, and in the air.
• Mammals also evolved but were small in size.
• Flowering plants appeared for the first time.
• Dinosaurs went extinct at the end of the Mesozoic.
Explore More
Use the time slider in this resource to answer the questions that follow.
• Evolution at http://johnkyrk.com/evolution.swf .
1.
2.
3.
4.
When did the Mesozoic Era begin?
What was the predominant type of animal during this time period?
When did placental mammals evolve? What were the first ones?
Describe the significant event that occurred at the end of the Mesozoic Era.
Review
1. Describe how the continents shifted during the Mesozoic Era.
2. Create a timeline of major evolutionary events during the Mesozoic Era.
3. Explain why scientists believe dinosaurs went extinct.
References
1. Dinosaur images from top to bottom: Nobu Tamura; Image copyright Computer Earth, 2014; Charles R.
Knight. The Mesozoic Era consists of the Triassic, Jurassic, and Cretaceous periods . Dinosaur images from
top to bottom: CC BY 3.0; Used under license from Shutterstock.com; Public Domain
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