I've looked into this, and there's no great way to do so, becuase the concept of species really just means large morphological changes. We assume everything is taxonomized (a tree), but in reality there is no tree--sometimes there is cross polination after some time apart. Ultimately they have a precise set of morphological criteria for each species, and they arrive at this criteria based on a sampling of animals and associating their morphology with their DNA.

They also use string similarity algorithms to determine morphological order, so we don't strictly know the order at the most precise level.

Of course, this is all very controversial, some people think we're always changing gradually and some people think we always change rapidly. I think they're both wrong--sometimes organisms change rapidly, and sometimes they change rapidly, depending on environmental factors.

disclaimer: I'm no expert, I've just looked at it from an algorithmic view and read some taxonomical texts as I had the same question as you.