Not phrenology, morphology. Morphology rooools. There’s no DNA in stuff this old *most of the time*. You’ve no doubt seen the T-Rex hemaglobin stories, FR has had a lot of duplicate topics for that matter. :’)
The way DNA is sometimes used to find common ancestry is to actually find very similar genes (those are three-basepair groups on a DNA strand, in this case a chromosome) in two different living samples, and try to estimate the length of time since the common source was identical and living.
I was just making fun of morphology. Haven’t there been errors made in classifications by morphology? Pandas, hyenas...
There seems to be great clarity in general classifications - mammal, reptile, fish, vertebrates/invertebrates - but doesn’t it begin to be more art than science at some level?