在1971年，古生物学家在怀俄明发现了地上的一个巨洞。这个洞口如同一个陷阱，不警觉的动物会坠入摔死。

　　They called it "natural trap cave".

　　人们称之为“自然陷坑”。

　　Laying 30 meters below the opening in an underground cavern, they found the remains of thousands of ice age mammals.

　　在洞口下方30米处的一个地下洞穴，他们发现了数千具冰期哺乳动物的遗骸。

　　Among them, the broken skeleton of a giant bear named Arctodus.

　　在其中有一头巨熊的破碎骨架，它叫熊齿兽。

　　The thing that impresses everybody when they first see an Arctodus fossil is just how big it is.

　　每个人第一次见到熊齿兽化石的时候都震惊于它的巨大。

　　The largest bears living today are the Alaskan Brown Bears, the Kodiak Bears and the Polar Bears.And an Arctodus would be about twice as large as either one of those.

　　如今生活的最大的熊，是阿拉斯加棕熊、科迪亚克熊，以及北极熊。而熊齿兽的体型是它们任意一个的两倍多。

　　The size of this bear was staggering.

　　这种熊的体型大得惊人。

　　Arctodus stood 4 meters tall, its body was 5 meters long and it weighed nearly a metric ton.It towered over today's Grizzlies.

　　熊齿兽站立起来有四米高，身体长五米，重量将近一吨。它远比现代灰熊更加高大。

　　Alongside its sheer mass, Arctodus had two distinctive features that differentiated it from modern bears.

　　除了体型巨大，熊齿兽还有两个特点让它们区别于现代熊。

　　The first was its oversized teeth and short, but powerful muzzle, from which it derives its nickname: the short faced bear.

　　第一是它们超大的牙齿和短而有力的口鼻部，因此它们有一个小名：短面熊。

　　This is the skull of a giant short faced bear and you can see why they're named this.

　　这是巨大的短面熊颅骨，能看出来它们为何得此名。

　　They have a very shortened snout in proportion to the overall skull, their skull is actually very wide for its size.

　　从整个头颅的比例来看，它们的口鼻部非常短，它们的头颅对它的大小来说是非常宽的。

　　Here are the canines, you can see they're very long and robust.

　　这些是犬齿，能看到它们很长很结实。

　　The teeth here are very bear-like.They're just basically bear teeth that are scaled up, developed for crushing.

　　这里的牙齿和熊的很像。它们基本上是放大了的熊牙，用来咬碎东西。

　　Very powerful muscles would have attached right here, here, and up here that would have given it a very powerful bite.

　　这里附着非常有力的肌肉，这里，还有上边这里，这能带来非常强大的咬合力。

　　We open the mouth then.We can see those large canines, what it would be like to be on the dinner side of a short faced bear.

　　我们把它的嘴张开。看到那些很大的犬齿，试想一下被短面熊当成晚餐会是什么样吧。

　　The second feature was its unusually long front legs.

　　第二个特点是它异乎寻常的长前腿。

　　Modern Grizzly bears have longer front legs than back legs.

　　现代灰熊前腿比后腿要长。

　　Allowing it to reach speeds of up to 35 miles per hour over short distances.

　　这使它能够在短距离就加速到35英里每小时。

　　But in the mega bear, both equal-length legs were a special adaptation that may have allowed this bear to reach speeds in excess of 45 miles per hour, and run for much greater distances.

　　不过这种巨熊，前后一样的长腿，是一种特别的适应性，那也许能让这种熊达到超过45英里的时速，而且能奔跑更长的距离。