Dinosaurs.
Publié le 15/05/2013
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protected their necks. Ankylosaurus was about 33 feet (10 meters) long.
ORNITHOPODS
Ornithopods were once the most numerous plant-eating dinosaurs.
There were many different kinds.Over time, ornithopods developed broad beaks.
These later ornithopods are called duck-billed dinosaurs.Some ornithopods were small and ran fast.
Others were huge.
Iquanodon, for example, was 25 feet (7.5 meters) long.
PACHYCEPHALOSAURS
These dinosaurs walked on two feet.
They had thick, dome-shaped skulls.
Scientists think they mayhave used their thick heads to butt other dinosaurs.
CERATOPSIANS
These dinosaurs ware also called horned dinosaurs.
One of the best-known ceratopsians was Triceratops. It had three horns on the top of its head: one horn on its snout and one horn above each eye.
Triceratops could reach lengths of up to 26 feet (8 meters) and weighed more than 12 metric tons.
WHAT HAPPENED TO THE DINOSAURS?
There are several theories about why dinosaurs died out.
Many scientists believe that there was asudden, violent event.
They think that an asteroid or comet collided with Earth.
Fire from the impactburned large areas.
Dust blocked sunlight from reaching the surface of Earth.
Acid rain fell everywhere.Plants could not grow.
There was no food for the plant-eating dinosaurs, so they died out.
Dinosaurs thatate plant-eating animals also died out.
Other scientists think that the environment changed.
Maybe the climate grew colder and dinosaursslowly became extinct over several million years.
Many scientists think that birds descended from a small kind of dinosaur.
If this is true, then dinosaurs,in a sense, are still alive in the form of modern birds.
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