Via the BBC I just found this rather wonderful image. It shows the explosion of types of mammal species that happened over time. If you download the complete pdf file (it's 1.6 MB) you can zoom all the way down to the individual species.

The tragedy is that this explosion of diversity is now being put into reverse, the next decades will see this tree becoming less, not more dense as man made extinctions wind back the evolutionary clock. Unless of course we do something about it.