20xx新東方考研英語強化新題型7選5-在線瀏覽
2024-10-25 01:14本頁面
【正文】 ow a great deal about many of them because their bones and shells have been preserved in the rocks as fossils. From them we can tell their size and shape, how they walked, the kind of food they ate. [C]The first animals with true backbones were the fishes, first known in the rocks of 375 million years ago. About 300 million years ago the amphibians, the animals able to live both on land and in water, appeared. They were giant, sometimes 8 feet long, and many of them lived in the swampy pools in which our coal seam, or layer, formed. The amphibians gave rise to the reptiles and for nearly 150 million years these were the principal forms of life on land, in the sea, and in the air. [D]The best index fossils tend to be marine creatures. These animals evolved rapidly and spread over large areas of the world. [E]The earliest animals whose remains ha
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