"We can usually tell"
But not always? So it's open to interpretation?
But not always? So it's open to interpretation?
We can easily tell with late model phyla. Early model phyla that have been extinct for a very long time can be out of effective reach of this backvectoring I've described for reconstructing extinct ancestral genome. Much like how we can use parallax to determine the distance of a few stars close to us, but it's useless for far away stars.
All it takes is one example of speciation to show speciation occurs. All it takes is one transitional form to show transitional forms exist and one organism from one higher taxon can evolve enough to occupy another higher taxon.
Although this isn't a direct answer to your question it is an answer for your implied assertion that any question of source or lack of information automatically negates any and all related conclusions.