xkcd digs into cladistics.
Unfortunately, his cladogram is wrong. Mammals should also be a subset of the reptiles, so the herpetologists should be demanding that all other amniotes be absorbed into their more inclusive field of tetrapod biology.
At least, until the ichthyologists show up and point out that we're all just weird dry land-walking fish.
Just to clear this up, I hope, here's a modified version of a cladistic diagram to show what herps are:
So if you want to avoid the sins of polyphyly or paraphyly, you must include birds and mammals in the herps. Of course, the alternative is to not care about the abstractions, and recognize that there are plenty of people already specializing in mammals and birds, so someone has to pay attention to all the otherwise neglected classes.