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It sounds like the story in a science fiction movie, but new research reveals some of the largest sea creatures living in what is now the Sahara Desert. It was found in an ancient body of water called the Trans-Sarahan Seaway, which covered parts of Western Africa 100 million to 50 million years ago.

For two decades, scientists examined fossils in present-day Mali to form an accurate picture of what this prehistoric environment looked like. They concluded the body of water was warm and shallow and was home to five-foot-long catfish and 40-foot-long sea snakes. The ancient Malian ecosystem had numerous predators including Crocodyliformes, Serpentes, and Amiidae, which were among the largest species at that time.

The Trans-Saharan Seaway ran north-to-south from what is now Algeria to what is now Nigeria. That means it was isolated from larger bodies of water during long periods of its existence. This may have limited number of enemies and ensured resources were always available, which is a perfect recipe for a species to grow.

"The Trans-Saharan Seaway exhibited the isolation from major seas," the researcher said. "This environmental variable may have created aquatic centers of endemism, stimulating the selection for gigantism as previously observed for species on terrestrial islands."

Endemism is when a species is confined to a specific area. The Sahara has obviously come a long way from the nightmare aquarium it once was. In 2014, climate simulations concluded the Sahara we know today was formed about seven million years ago when a shift in tectonic plates closed off the region from the surrounding seas.

1.What did people think of the sea creature in the Sahara Desert?

A It was strange.

B It was expensive.

C It was lost.

D It was new.

解析：选A。推理判断题。根据文章第一段第一句的It sounds like the story in a science fiction movie...可以得知这像是科幻故事，因此在撒哈尔沙漠发现的海洋生物让人感觉到奇怪，故选A。

2.What was the character of Crocodyliformes?

A They lived a long life.

B They looked like sea snakes.

C They were large in size.

D They enjoyed the cold water.

解析：选C。推理判断题。根据文章第二段最后一句...which were among the largest species at that time可以得知这些动物的形体巨大，故选C。

3.What made the sea creature grow well?

A The hot weather.

B The enough air.

C The special isolation.

D The growth of plants.

解析：选C。推理判断题。根据文章第三段第二句和第三句That means it was isolated from larger bodies of water during long periods of its existence. This may have limited number of enemies and ensured resources were always available...可以得知与其他地方隔离，从而确保了这种生物有足够的食物并且没有天敌，故选C。

4.What is the main idea of the last paragraph?

A The Sahara has its endemism.

B The Sahara has a long history.

C The nightmare aquarium appeared.

D The tectonic plates happened.

解析：选A。主旨大意题。根据文章最后一段第一句Endemism is when a species is confined to a specific area.以及本段内容可以得知该段讲述的是撒哈尔沙漠的生物独特性，故选A。