The four-toed Eohippus preceded the three-toed Miohippus, for example, but North American fossil evidence suggests a jerky, uneven transition between the two.

例如，四趾的始祖鸟先于三趾的始祖鸟出现，但北美的化石证据表明，这两种动物之间有一个急促而不均衡的转换过程。