它们的牙齿后弯曲，这意味着它们开始指向后方，它们也是很像利刃边缘呈锯齿状。

　　Three tons of terror moving at 30 miles an hour would have been a stunning sight.

　　三吨重的恐怖猛兽以20英里的时速移动，这可会是惊人的一幕。

　　What made them even more fearsome was that they hunted in packs.

　　让它们更加可怕的是它们成群狩猎。

　　We've collected in fact 12 good skeletons in southern Alberta.

　　事实上我们在阿尔伯塔南部找到了十二具完整骨骸。

　　In addition to that, we have a bone bed that Barnum Brown worked in 1910 where we have parts of 23 skeletons of Albertosaurus.

　　除此之外，巴纳姆·布朗1910年时考察过的骨床有部分二十三副阿尔伯特龙的骨骸

　　And these are everything from 2-year-olds to 25-year-olds.

　　这些从两岁到二十五岁的都有。

　　As adults, as juveniles, or sub-adults or we called teenagers, all found together at the same time at the same place.

　　成年恐龙、幼年恐龙还有快成年的青年恐龙，都在同一时间同一地点被发现。

　　And this suggested that they may have operated in family groups,so they may not have nearly been very powerful predators, they may have be very powerful pack hunting predators.

　　这表明它们可能以家庭为单位进行活动，也许它们不是那么厉害的掠食者，但它们会是非常厉害的群体掠食者。

　　Fossils of varying sizes have been found very closely together pointing to the fact that Albertosaurus may have lived in family units.

　　尺寸不一的化石在相距甚近的地方被发现表明阿尔伯特龙有可能以家庭为单位活动。

　　This would have increased the survival of their young and helped the Albertosaurus expend its territory.

　　这样能增加它们幼崽的生存机会也能帮助阿尔伯特龙拓展势力范围。

　　But even these well-adapted dinosaurs were vulnerable to climate change.

　　不过即使这些适应力很强的恐龙在气候变化面前也不堪一击。

　　In the late Cretaceous period, temperatures inexplicably began to climb.

　　在晚白垩纪时期气温莫名地又开始攀升。

　　A pretty dramatic change in the climate was becoming obvious at the end of the Cretaceous.

　　这一气候上相当剧烈的变化在白垩纪末期变得愈发明显。

　　We find fossil evidence of cold-blooded animals and plants that don't really tolerate the cold that well being found in the polar regions.

　　我们在极地地区发现了一些不能忍受寒冷的冷血动物和植物的化石证据。

　　Why the earth began to warm after the cooling period is still a mystery.

　　地球为什么在寒冷时期之后又开始变暖现在仍是个迷。

　　One interesting hypothesis involves the larger amounts of water that once covered much of the earth.

　　一种有趣的假说用曾经大量覆盖地球的水来解释。

　　Rather than absorbed the heat, they may have radiated it back into the atmosphere and cause a green house effect.

　　它们不是吸收热量，而是将其反射到空气中形成温室效应。

　　Whatever the case, these changes were tough to deal with for some dinosaurs, especially those up north.

　　无论是为什么，这些变化对一些恐龙来说并不好对付，特别是在北面生活的那些。

　　As temperatures rose in the late Cretaceous period, lush foliage grew, supporting larger and larger herbivores.

　　随着白垩纪晚期气温回升，茂盛的植物大量生长，供养着越来越大的植食动物。

　　These giant plant eaters like Triceratops developed horns for protection.

　　这些像三角龙一样的巨大的植食者进化出角来进行防御。

　　The meat eater also adapted.

　　食肉者也随之而改变。

　　The result was a predator whose name instills fear even today.

　　结果是一种名字即使是今天也让人胆寒的掠食者。

　　The king of the dinosaurs - Tyrannosaurus Rex.

　　恐龙之王，雷克斯暴龙。

　　Tyrannosaurus Rex is without a doubt the biggest and baddest predator that ever walked North America and quite possibly the world.

　　雷克斯暴龙毫无疑问是北美地区很可能是全世界出现过的最大最厉害的掠食者。

　　They first appeared during the late Cretaceous about 68 million years ago and lived right up to the extinction of the dinosaurs about 3 million years later.

　　它们最早出现于白垩纪晚期大约六千八百万年前，一直生活到三百万年之后恐龙灭绝的时候。

　　Their range included Montana, Wyoming, Colorado, New Mexico, South Dakota and Canada, and even as far south as Texas.

　　它们分布于蒙大拿州、怀俄明州、科罗拉多州、新墨西哥州、南达科他州和加拿大，甚至最南达到德克萨斯州。

　　T-Rex stood out as the largest predator.

　　霸王龙是出类拔萃的最大掠食者。

　　It weighed up to seven tons, stood nearly five meters tall, and measured thirteen meters in length.

　　重量可达七吨，站立高度近五米，长度为十三米。