1 . The Smilodon and the Tiger

The smilodon (剑齿虎) died out probably about ten thousand years ago._______it is also known as the saber-toothed tiger, it was not a_______relative of the modern tiger. The more scientists_______the two big cats, the more_______they find.

Tigers are not_______animals. They generally travel by themselves. The smilodon, on the other hand, probably_______in groups. Tigers run fast while_______their prey (猎物). But the smilodon, with much_______tails than today’s tigers, did not have the balance to run at_______speeds. It probably caught its prey by________quietly until an animal came near. Then, the smilodon would________its prey.

Another main difference between today’s tiger and the smilodon is the size of the smilodon’s________. It is known as a saber-toothed cat________two huge teeth that grew from the top of its jaw (颌). These teeth grew up to nearly 18 cm long and were easily________and damaged. The smilodon probably used the teeth to bite into________parts of its prey’s body, such as its stomach. A modern tiger's teeth are much smaller, but they are________.

The smilodon lived in North and South America from about two million years ago until about ten thousand years ago. Tigers,________, still exist today and live in eastern and southeastern Asia. No one knows for sure why the smilodon________. However, scientists do know that many of today’s tiger species are in danger of________because of human activity. So it is important to________tigers and many other animals.