More evolution stuff
This diagram from a Nature Letter is good. Not as good as the wikipedia one. But it's not quite the same picture.
What it shows is how divergence actually occurs. A lot of people look at Phylogenic trees, and see them as gradual splits. They see it as Primary form transforms into two (or more) secondary forms. Which is essentially right. But what they don't see the transitory period.
Here we see primary form (reptilian ancestor) split into two forms of the same primary form (still reptilian ancestor, just split), which then graduate into the modern forms (mammals and birds). The Synapsids and Diapsids are still reptilian (and as you can see from the pictures superficially similar), but they have diverged enough by the 310MYA mark that they don't intermingle anymore, and gradually they become more and more different.
Of course the diagram, like most, is incomplete. You could show the third branch of reptiles that remained reptiles, as well as the many side branches off the left and right chains. But its just there for a simple representation. And it does the job well.