00:25Millions of years ago, long before the first men walked the earth,
00:30giant reptiles called dinosaurs ruled our world.
00:55About 65 million years ago, the last dinosaurs died out. A world catastrophe may have killed
01:02them, but no one knows for sure what happened.
01:10Whatever the reason, the disappearance of the dinosaurs marked the end of an era in the
01:14earth's history and the beginning of a new one, the Cenozoic era, the age of mammals.
01:49What are mammals?
01:52Unlike fish and modern reptiles, which are cold-blooded, mammals are warm-blooded.
01:57This enables them to adapt better to changes in temperature and environment.
02:08Birds, most reptiles and fish lay eggs, while most mammals give birth to their young live
02:21and suckle them with milk.
02:32Usually, mammals have hair or fur to protect them and keep them warm.
02:39Earth is approximately five and one-half billion years old. Animal life first appeared over
02:45three billion years ago. Fish began here. Then came the amphibians and reptiles. The age of
02:54reptiles began about 230 million years ago and ended about 65 million years ago, which was the beginning of the
03:02Cenozoic era, the age of mammals.
03:07The first primitive mammals appeared during the age of reptiles. Small mammals such as this deltatherium, seen here eating a
03:16dinosaur egg, resembled the opossums and shrews of today.
03:24This Eohippus was the ancestor of our modern horse, but was only the size of a small dog.
03:31He originated in North America 55 million years ago.
03:36Unlike the modern horse which has hooves, Eohippus had claws. During the next 55 million years, he evolved, gradually growing
03:48larger and losing his extra toes.
03:51The middle toe grew longer and the toenail became a hoof.
03:56Almost two million years ago, the modern horse called Equus appeared.
04:00He traveled by land bridge through Alaska to Asia. In time, he died out in North America.
04:08But thousands of years later, he was brought back to America by European explorers.
04:13Like the horse, all animals which are alive today are related to animals which lived long ago.
04:22Early mammals were generally small and were preyed upon by larger animals.
04:29Such as the flesh-eating bird, Diatrema, which grew nearly nine feet tall.
04:50A few mammals grew to enormous proportions.
04:54Of all the mammals that ever lived on land, the Belucotherium was the largest, standing twice as tall as any
05:01modern elephant.
05:03Although it had no horn, the Belucotherium was actually a species of rhinoceros.
05:14One of the strangest-looking primitive mammals was the platybelodon, an ancient relative of the elephant.
05:21His lower tusks and long, curved jaw formed a shovel-like mouth which he used to scoop up his food.
05:34The glyptodon was a giant armored mammal related to the modern-day armadillo.
05:41From head to tail, he measured close to 12 feet in length.
05:52The Megatherium was a giant ground sloth.
05:55He was a slow, awkward animal.
05:58Although he usually walked on all four legs, the Megatherium was able to rear up on his hind legs to
06:04reach tree leaves, using his claws to pull down branches.
06:14One of the fiercest prehistoric mammals was the saber-toothed cat, Smilodon.
06:21Armed with large, curved teeth and sharp claws, he could kill animals twice his size.
06:38Even though this Smilodon is hungry, he's not foolish enough to attack the armored glyptodon.
06:44Instead, he decides to look for easier prey.
06:57The End
07:05The End
07:34About two million years ago, the world's climate began to change and grow colder.
07:40Great fields of ice called glaciers covered many parts of the earth near the poles.
07:46While some areas stayed warm, others grew very cold.
07:51This period was the beginning of the Ice Age.
07:57Many of the mammals could not adapt to the new climate and became extinct.
08:02Others, such as this woolly mammoth, developed thick, hairy coats to protect them from the cold.
08:10Preserved remains of mammoths have been found in the permanently frozen ground of Siberia and Alaska.
08:24One mammal was different from all the others.
08:27Man.
08:30Although his body was small and weak, his brain was large.
08:36Man's intelligence gave him a means to survive.
08:40When it became too cold, he made clothes to keep himself warm.
08:45He made weapons to protect himself.
08:48And also tools, which he used in many ways.
08:53Man soon ruled the earth.
08:58From humble beginnings, mammals developed to become masters of the earth.
09:13Man has existed only a few million years, a very short period in the history of earth.
09:21With his superior intelligence, man is the first and only mammal with the ability to change the world around him.
09:30Will man survive?
09:34The choice is ours.
10:02By God, we have done so much work.
10:05By Stuff, we are Siri, are one of the-
10:06By Stuff, we are Megan wrote himself, is the forest.
10:06That's what something he wishes to do.
10:06Why will this when we become Sophomore, why will he be in the U Dob ate for ideologies?
10:07Ping or a couple of languages.
