此外，海象和海豹用它们的后鳍推动自己在水中运动，而海狮用它们的前鳍。

Moreover, walruses and seals drive themselves through the water with thrusts of their hind flippers, but sea lions use their front flippers.

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前肢，上肢动物前部的附肢，如前腿、前翅、前鳍等。

An anterior appendage, such as a leg, wing, or flipper.

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在波兰东南部的圣十字山的一座废弃的采石场，（科学家）曾发现过动物脚印的化石，经鉴定，为3.95亿年前形成，比发现的最古老的四角龙（一种拥有四肢而非鳍的脊椎动物）化石要早1.8亿年。

In early January 2010, another group of scientists found the oldest fossilized footprints made by a four-legged creature

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