But in just those couple million years  without megalodons whale populations exploded.

但是，就在没有巨齿鲨的几百万年里，鲸鱼的数量激增。

But if megalodons were so powerful, why did they go extinct?

但是，如果巨齿鲨如此强大，为什么它们会灭绝呢？

Because megalodons were highly mobile predators, their extinction had global consequences.

由于巨齿鲨是高度机动的掠食者，它们的灭绝产生了全球性的后果。

With a body made for killing giants, baby megalodons were under a  lot of pressure to grow quickly.

拥有为杀死巨人而生的身体，小巨齿鲨承受着快速生长的巨大压力。

Reconstructing their jaws, researchers think megalodons could eat a now-extinct 7-meter sperm whale in as few as four bites.

重建它们的下颚，研究人员认为巨齿鲨可以在短短四口咬下吃掉现已灭绝的7米抹香鲸。

Experts believe these were nurseries that supported countless generations of budding megalodons.

专家认为，这些苗圃支持了无数代萌芽的巨齿鲨。

Like many sharks, megalodons could shed and replace thousands of teeth over the course of their lives.

像许多鲨鱼一样，巨齿鲨可以在一生中脱落并更换数千颗牙齿。

Because their skeletons were cartilaginous, what remains of megalodons are mostly scattered clues, like some isolated vertebrae and lots of their enamel-protected teeth.

因为巨齿鲨的骨骼是软骨质的，所以留下的大部分都是零散的线索，比如一些孤立的椎骨和许多受牙釉质保护的牙齿。

Environmental changes may have made megalodons vulnerable and increasingly put them in competition with other predators, including the great white shark, a relative newcomer.

环境变化可能使巨齿鲨变得脆弱， 并越来越多地使它们与其他捕食者竞争，其中包括相对较新的大白鲨。

And the fossilized bones of ancient cetaceans do indeed show evidence of megalodon bite marks— including some that healed over, confirming that megalodons pursued live prey.

古代鲸目动物的骨骼化石确实显示了巨齿鲨咬痕的证据， 其中一些已经愈合，这证实了巨齿鲨追逐活的猎物。

Looking at the similarities with great white shark teeth, scientists estimate that megalodons might have stretched up to 20 meters— three times longer than great whites.

通过观察与大白鲨牙齿的相似之处，科学家估计巨齿鲨可能已经伸展到20米 - 比大白鲨长三倍。