What are the rules of phylogeny classification?
To me there are three, and these are, one, superposition of geological strata giving us an order through time, and two, faunal succession, the observation that the faunas change through that giving us a sense of their evolution and dividing up into classes over geological time. And then I would say that the third principal is the idea of intermediacy, or continuity from sample to sample, as the evidence that they are related so that we wind up tracing lines up through geological strata, often in very broad brushstrokes in the sense of tracing mammals as a group through the geological strata from their origin in the Triassic and the Mesozoic to the big diversification at the beginning of the Cenozoic and up to their abundance today. Or tracing smaller lines within a group, like horses and other odd-toed perrisodactyls up through time to understand their history. So the intermediates are important evidence of transitions. Does this hold up at any level of taxa? Yes it does, but of course
