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Now listen to part of a lecture on the topic you just read about.
现在来听一段有关你刚刚读到的话题的演讲。
The hypothesis that the Edmontosaur migrated every winter is not convincing.
埃德蒙顿龙每年冬天迁徙的假设没有说服力。
First, the Edmontosaur did not have to migrate to find food.
首先，埃德蒙顿龙不需要迁徙去寻找食物。
One hundred million years ago, the summer temperatures in the North Slope area were warmer than they are today.
在一亿多年年前，北坡地区的夏日气温比现在要暖和。
And remember, in arctic regions like the North Slope, the Sun shines 24 hours a day at the peak of the summer.
而且，别忘了，在像北坡一样的北极地区，夏天高峰太阳24小时都照耀着。
The warm temperatures and extensive daylight created incredibly good growing conditions for plants,
暖和的气温和充足的日照为植物提供了好到难以置信的生长条件，
so much vegetation was produced during the summer that when the vegetation died as the winter came,
夏天里生出了太多的植物，当植物因为冬天来临而死去的时候，
there was a lot of nutritious dead vegetation around in the winter.
冬天里有很多营养的死去的植物。
The Edmontosaur could have easily lived on the dead plant matter during the winter.
埃德蒙顿龙可以轻松地依靠这些死去的植物度过冬天。
Second, just because Edmontosaurs lived in herds doesn't mean they migrated.
第二，埃德蒙顿龙成群的生活，不表示它们会迁徙。
Animals live in herds for many other reasons.
动物们因为很多别的原因而群居。
Living in herds, for example, provides animals with extra protection from predators.
比如，成群的生活，给动物们提供了额外的保护，以抵其猎食者。
Having extra protection is useful even for the animals that live in the same area the whole year round.
额外的保护对那些常年居住在同一个地方的动物们来说也是很有用的。
A modern example of this is the Roosevelt elk—a large plant-eater.
一个现代的例子就是罗斯福马鹿，一种大型的草食动物。
Roosevelt elks live in the forests of the western United States.
罗斯福马鹿住在美国西部的森林里，
They live in herds but they do not migrate.
它们群居，但是它们不迁徙。
Third, although adult Edmontosaurs were capable of migrating long distances, what about Edmontosaurs that were not yet adults?
第三，即使成年埃德蒙顿龙能够长度迁徙，那些未成年的埃德蒙顿龙们怎么办呢？
Juvenile Edmontosaurs were not physically capable of travelling the great distances required to reach warmer territories
新生的埃德蒙顿龙生理上不具备去更温暖的领域所需要长途跋涉的能力，
and would have slowed the herd so much that the herd never would have made it to its destination.
会大大拖慢兽群的速度，导致兽群永远到不了目的地。
The herd could not have left the juveniles behind because the juveniles would not have survived on their own.
而兽群也不会留下这些新生儿不管，因为新生儿不能独立生活。
So the whole herd had to stay where they were and survive on the cold North Slope.
所以整个兽群只好留在它们所在的地方，靠北坡生存下去。
