During this time, all of the three-toed horses and most other monodactyls died out.

在此期间，所有的三趾马和大多数其他单趾动物都灭绝了。

That is, until yet another new adaptation appeared: Several descendants of Merychippus became monodactyls, meaning they had only one toe.

也就是说，直到另一种新的适应出现：Merychippus 的几个后代变成了单趾动物，这意味着它们只有一个脚趾。