Travel back in time for a show that was millions of years in the making.

Welcome to the Mesozoic (meh-zuh-ZOH-ik) Era!
This was the time when dinosaurs great and small walked the Earth. The Mesozoic Era lasted about 180 million years. During this time, more and more dinosaur species appeared. Many grew to be gigantic, and some were the fiercest predators around. By the last part of the era, dinosaurs really ruled. That’s why the Mesozoic is also called “The Age of Dinosaurs.”

The Mesozoic Era was divided into the Triassic (try-YASS-ik) Period, the Jurassic (joo-RASS-ik) Period, and the Cretaceous (krih-TAY-shus) Period. It was like an amazing prehistoric play with three acts. Each act had its own scenery and characters that changed over time.
Ready for the curtain to go up? Then turn the page—Act One is about to begin!

MESOZOIC ERA
(248–65 million years ago)

FEATURING

TRIASSIC
(248–205 million years ago)

JURASSIC
(205–138 million years ago)

CRETACEOUS
(138–65 million years ago)

ACT ONE – TRIASSIC PERIOD

SETTING THE SCENE
At the beginning of the Triassic Period, the Earth was a very different place from what it is today. All of the continents were joined together to form one “supercontinent” called Pangaea (pan-JEE-uh). Pangaea was surrounded by a huge ocean. The weather back then was mostly hot and dry, and there were no polar ice caps. Palm-like trees, ferns, mosses, and other plants grew. Amphibians, reptiles, spiders, and rodent-sized mammals were some of the animals that lived on land, while fishes, squids, and reptiles swam in the ocean.

STARS OF THE SHOW
Before the Triassic Period, something caused many of the animals that lived then to die out. So when the earliest dinosaurs appeared during the Triassic, there was a lot of space for them and less competition for food—great conditions for more and different kinds of dinosaurs to begin their rule.

COELOPHYSIS (see-loh-FYE-sis)

• SIZE: Waist-high to a grownup; 8 to 9 feet long
• DIET: Meat (Fossil remains of small reptiles and fish have been found in the stomachs of Coelophysis fossils.)
• FUN FACT: In 1998, astronauts took a Coelophysis skull to the Russian space station Mir as a symbol of Earth’s history. At the end of their mission, they returned it to the museum it had come from.

EORAPTOR (EE-oh-rap-tor)

• SIZE: About the same as a large dog
• DIET: May have eaten both plants and animals
• FUN FACT: Scientists first thought Eoraptor was an early relative of meat-eating dinosaurs. But now they believe its later relatives were long-necked plant-eaters.

EODROMAEUS (ee-oh-DROH-mee-us)

• SIZE: Knee-high to a grownup; 4 feet long
• DIET: Meat
• FUN FACT: This dino was only a little bigger than a large dog. But it was the great-great-a-million-greats grandparent of T. rex!

MELANOROSAURUS (meh-LAN-oh-roh-sawr-us)

• SIZE: 35 feet long
• DIET: Plants
• FUN FACT: Able to rear up on its tree trunk-like legs to nibble treetops, Melanorosaurus was one of the longest dinos of its time. (Some later dinos got more than four times longer!)

ACT TWO – JURASSIC PERIOD

SETTING THE SCENE
During the Jurassic Period, Pangaea began to break up, splitting into a top and bottom half. The ocean spilled into the space between. This changed the climate from hot and dry to warm and moist, with lots of rain. Lush green plants filled new rainforests. There was an explosion of life, as more and more kinds of animals appeared, both on land and in the ocean.

STARS OF THE SHOW
During this time, some of the small, plant-eating dinosaurs that had lived during the Triassic eventually evolved into gigantic dinos weighing many tons. Some meat-eating dinosaurs also became larger and fiercer, and more and more dinosaurs of all kinds appeared.

DIPLODOCUS (dih-PLOD-uh-kuss)

• SIZE: 90 feet—as long as three school buses
• DIET: Plants
• FUN FACT: Scientists think Diplodocus ate by sliding its teeth along branches sideways, in order to strip off lots of leaves at a time.

COMPSOGNATHUS (komp-sug-NAY-thus)

• SIZE: About the size of a turkey
• DIET: Meat
• FUN FACT: Not all Jurassic dinos were giants. For a long time, Compsognathus held the title of World’s Smallest Dinosaur. But recently, the fossils of even smaller dinosaurs have been discovered.

ALLOSAURUS (AL-uh-sawr-us)

• SIZE: 40 feet long
• DIET: Meat
• FUN FACT: Allosaurus was the biggest, baddest predator of its time. It preyed on plant-eating dinosaurs, ripping and tearing them apart with its long, sharp teeth.

STEGOSAURUS (STEG-uh-sawr-us)

• SIZE: 28 feet long
• DIET: Plants
• FUN FACT: Like many other dinosaurs that ate plants, Stegosaurus also swallowed rocks—on purpose! The rocks helped to crush all the leaves and other plant parts in the dinosaurs’ stomachs.

ACT THREE – CRETACEOUS PERIOD

SETTING THE SCENE
During the Cretaceous Period, Pangaea continued to break apart into separate continents. By the end of the period, the continents looked pretty much the way they look today. Another big change was that flowering plants became really widespread. Along with the flowers came insects such as bees and wasps. Mammals were still small creatures scurrying along fern-covered forest floors.

STARS OF THE SHOW
The Jurassic Period is probably the most famous dinosaur time period because of the Jurassic Park movie and its sequels. But the Cretaceous Period was really the peak of the dinosaurs’ rule. There were more kinds of dinosaurs than ever before—from huge plant-eaters quietly munching leaves to monstrous predators terrorizing anything that got in their way.

TYRANNOSAURUS REX (tye-RAN-uh-sawr-us REX)

• SIZE: 42 feet long
• DIET: Meat
• FUN FACT: One of the biggest T. rex fossils ever found is on display at The Field Museum in Chicago, Illinois. This big, toothy monster is nicknamed “Sue,” after the paleontologist who discovered it. (A paleontologist [pay-lee-un-TAH-luh-jist] is a scientist who studies fossils.)

ANKYLOSAURUS (ang-KYE-luh-sawr-us)

• SIZE: 35 feet long
• DIET: Plants
• FUN FACT: A cousin of Stegosaurus, Ankylosaurus was known as an “armored dinosaur” because it was covered with bony plates. It may have used its club tail as a weapon. Did you see it in the movie Jurassic World?

SPINOSAURUS (SPY-nuh-sawr-us)

• SIZE: 50 feet long
• DIET: Meat
• FUN FACT: Scientists believe Spinosaurus was the biggest dinosaur predator, even bigger than T. rex. It had a “sail” on its back as tall as a grownup and is believed to be the first swimming dinosaur.

TROODON (TROH-uh-don)

• SIZE: Shoulder-high to a grownup
• DIET: Meat, perhaps plants
• FUN FACT: Troodon dinosaurs laid their eggs in nests on the ground. The parents may have taken turns keeping the eggs warm.

EXTINCTION
About 65 million years ago, the curtain came down on the Age of Dinosaurs. Scientists don’t know for sure what caused the extinction of the dinos. The most popular ideas are that a space rock such as an asteroid or a comet hit the Earth, or that there were massive volcanic eruptions. Some scientists think both may have happened. Whatever the cause, it was the end for the dinosaurs. And once the dinosaurs were gone, it was the mammals’ turn to take the stage.

 

“The Greatest Show on Earth” originally appeared in the November 2015 issue of Ranger Rick magazine.
(Click on each image above for a closer view of the story.)