Mesozoic Era - The Age of
Dinosaurs
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
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Printed: July 21, 2012
AUTHORS
Douglas Wilkin, Ph.D.
Jean Brainard, Ph.D.
www.ck12.org
C ONCEPT
1
1
Mesozoic Era - The Age of
Dinosaurs
• Explain why the Mesozoic Era is called the age of 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 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=watgb11LOHE
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.
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.
Concept 1. Mesozoic Era - The Age of Dinosaurs
2
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FIGURE 1.1
The Mesozoic Era consists of the three periods described here.
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.
MEDIA
Click image to the left for more content.
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
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3
where the dinosaurs left off?
Vocabulary
• dinosaur: A diverse group of reptiles; the dominant terrestrial vertebrates for 135 million years, from the
beginning of the Jurassic (about 200 million years ago) until the end of the Cretaceous (65.5 million years
ago).
• Gondwanaland: Southern supercontinent that separated from Pangaea; today’s Southern Hemisphere continents.
• Laurasia: Northern supercontinent that separated from Pangaea; today’s Northern Hemisphere continents.
• mass extinction: Extinction event in which many if not most species abruptly disappear from Earth.
• Mesozoic Era: Age of dinosaurs that lasted from 245–65 million years ago.
• Pangaea: Supercontinent of all the major land masses; formed during the Permian Period.
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.
Practice I
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?
Describe 4 significant events that occurred during the Mesozoic Era.
When did placental mammals evolve? What were the first ones?
Describe the significant event that occurred at the end of the Mesozoic Era.
Practice II
• Identify the Prehistoric Animals at http://www.neok12.com/diagram/Prehistoric-Animals-01.htm.
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.
Concept 1. Mesozoic Era - The Age of Dinosaurs