Mammals today are all part of what's called crown group Mammalia.

今天的哺乳动物都是所谓的冠群哺乳动物的一部分。

A crown group includes all of the living members of a group back to its most recent common ancestor.

一个皇冠群包括一个群中所有活着的成员，这些成员可以追溯到它最近的共同祖先。

For crown group mammals, our most recent common ancestor is the one shared by placentals like us, marsupials like the kangaroo, and the monotremes like the platypus.

对于冠群哺乳动物，我们最近的共同祖先是像我们这样的胎盘动物、袋鼠这样的有袋动物和鸭嘴兽这样的单孔类动物共有的祖先。

And the ancestors of the crown group would diversify into all the different mammals we know today, united by those four classic mammalian traits, while the last of the ancient mammaliaforms would die out.

冠群的祖先会分化成我们今天所知道的所有不同的哺乳动物，由这四种经典哺乳动物特征结合在一起，而最后一种古代哺乳动物将会灭绝。

Now, just outside the crown group are its extinct relatives - the ones that branched off before the common ancestor of the crown, but are still more closely related to the crown group than to anything else.

现在， 就在冠群之外的是它已灭绝的亲属——那些在冠群的共同祖先之前分支出来的，但与冠群的关系仍然比与其他任何事物的关系更密切。