最近出土的化石使鲸的祖先可追溯到一种有蹄外形像狗的植食动物，而且基因分析证实了现存动物中河马是鲸的近亲。
Recently unearthed fossils trace whales to a doglike predecessor of hoofed plant-eaters, and genetic analysis has identified hippos as whales' closest living relatives.
在旧石器时代晚期，人类开始艺术性地表达思想，在岩洞里描绘了大量大型动物的形像。
When humans began to express themselves artistically, in the late Paleolithic era, they drew hunts of large animals on the walls of caves.
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