2)__________________ . Nearly all of the fossils that we know were preserved in rocks formed by water action, and most of these are of animals that lived in or near water. Thus it follows that there must be many kinds of mammals, birds, and insects of which we know nothing.
本段话题: 水保存动物化石 关键词:water
3)_____________________ There were also crab-like creatures, whose bodies were covered with a horny substance. The body segments each had tow pairs of legs, one pair for walking on the sandy bottom, the other for swimming. The head was a kind of shield with a pair of compound eyes, often with thousands of lenses .They were usually an inch or tow long but some were 2 feet.
本段话题: 像蟹一样的早期海洋动物 关键词:crab-like creatures
4)_______________________. Of these, the ammonites are very interesting and important. They have a shell composed of many chambers, each representing a temporary home of the animal. As the young grew larger it grew a new chamber and sealed off the previous one. Thousands of these can be seen in the rocks on the Dorset Coast.
本段话题: 甲壳动物 关键词:ammonites, shell
5)______________
About 75 million years ago the Age of Reptiles was over and most of the groups died out. The mammals quickly developed, and we can trace the evolution of many familiar animals such as the elephant and horse. Many of the later mammals, though now extinct, were known to primitive man and were featured by him in cave paintings and on bone carvings.
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