Toothed whales, they found, are living on the edge, size-wise.

他们发现就体型而言，齿鲸生活在危险边缘。

Toothed whales thus do seem to have hit some sort of size limit.

因此，齿鲸似乎确实有某种体型上的限制。

Broadly, big whales come in two varieties. Toothed whales, such as sperm whales, hunt individual prey.

总的来说，大鲸鱼有两种。齿鲸，如抹香鲸，捕食单个猎物。

Indeed, some toothed whales and bats emit sound pulses around 200,000 hertz and listen for the reflections.

事实上，一些齿鲸和蝙蝠会发出 20 万赫兹左右的声脉冲收听反射声。

Light doesn't travel well underwater. So dolphins and other toothed whales navigate like bats, using echolocating clicks.

光在水中会衰减。所以海豚和其他齿鲸类动物在水中用回声定位，就像蝙蝠一样。

They have very keenly developed echo location sonar sense associated with their brains that is a unique feature of toothed whales.

它们有与大脑相关的非常发达的回声定位声纳感觉，那是齿鲸独一无二的特点。

And with that, they've evolved from being toothed whales.

因此，它们已经从齿鲸进化而来。

They are smaller, but a bit scarier as they are the biggest of the toothed whales.

它们体型较小， 但更可怕，因为它们是齿鲸中体型最大的。

Toothed whales and pinnipeds, like seals and sea lions, might have competed with the giant penguins for food.

齿鲸和鳍足类动物， 如海豹和海狮，可能与巨型企鹅争夺食物。

Nah, the difference in size is too big: sperm whales can reach 62 ft in length, which makes them the largest toothed whales in the world.

不会的，它们的体型相差太大了：抹香鲸的体长可达 62 英尺，是世界上最大的齿鲸。

And the cause might have been the rise of marine mammals, especially new groups of toothed whales that happened in the Oligocene Epoch.

原因可能是海洋哺乳动物的兴起，尤其是渐新世时期出现的新齿鲸群。

Meanwhile, toothed whales do use echolocation, and they and other species of baleen whales make social sounds, such as cries and whistles, to communicate.

同时，齿鲸确实使用回声定位，它们和其他种类的须鲸会发出社交声音（例如叫声和口哨声）进行交流。

Model tests have shown that frequencies around 1 kilohertz (the preferred bandwidth of seals and toothed whales) can be reduced by up to 22 decibels, at slow speeds.

模型测试表明，在低速下，1千赫兹左右的频率（海豹和齿鲸的首选带宽）可降低多达 22 分贝。

Lots of different features also help animal ears hit especially high notes, like the extra hard, stiff middle ear bones of toothed whales; like dolphins and sperm whales, which efficiently propagate high-frequency vibrations.

许多不同的特征也有助于动物的耳朵捕捉特别高的音调，比如齿鲸的中耳骨特别坚硬，像海豚和抹香鲸一样，能有效地传导高频振动。