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More than 65 million years ago, at the end of the Cretaceous Period（白垩纪）, many species died off during a global disaster often called the K-Pg extinction. The end of the Cretaceous Period saw some very big changes in Earth’s oceans and on its lands. It wiped out up to 80% of all animal species, including the dinosaurs. But 20% of the animals that were alive with the dinosaurs did survive. What were these amazing animals? How and why did they survive while so many others disappeared forever? Behold the survivors of the K-Pg mass extinction.

Spider （Arachnid）

The earliest web-spinning arachnids （蛛形纲动物）produced silk from their abdomens about 386 million years ago. These ancient arachnids are closely related to today’s spiders. The original function of spider webs was probably to wrap eggs in a protective covering. Later, spiders evolved to use their silk to spin webs for catching prey. This ingenious invention helped them save energy while hunting and made it easier for them to survive.

Dragonflies （Meganeura 巨脉蜻蜓）

Today these flying insects have wings with a span of about 6 inches. But the earliest dragonflies used to grow to huge sizes 325 million years ago. The Meganeura dragonfly had a wingspan of almost 27 inches and would have dwarfed the largest modern dragonfly. In the oxygen-rich swamp environment of the Cretaceous, their large size helped Meganeura to absorb needed oxygen. But after the K-Pg extinction, the air and water contained less oxygen. Dragonflies adapted to their new environment by becoming smaller.

Crocodile （Sarcosuchus 帝王鳄）

The largest Sarcosuchus from the Cretaceous was 39 feet long. This is three times longer than the biggest modern crocodile. Crocodiles are predators and have probably hunted in much the same way for the past 225 million years. They have survived all this time by matching their relatively small size with their extremely powerful jaws that produce a great biting force.

Answer the following questions in complete sentences.
1．When did the K-Pg extinction happen?
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2．How did spiders survive?
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3．What were Meganeura’s large-sized wings used for?
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4．Dragonflies didn’t become smaller to adapt to the new environment, did they?
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5．Compared with crocodiles today, did crocodiles 225 millions ago hunt differently or similarly?
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