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A species is not a discrete thing to begin with. Life is gradient at all stages, and we'll never be able to test any hypothesis about how closely related any two similarly structured dinosaurs are. Short of freezing eggs, we have no data whatsoever on the question of how far an organism can evolve before it becomes genetically incompatible with its own ancestors. What we need to be looking at isn't essays on the topic, trying to convince us one way or the other, but a mapped probable timeline of the complete evolution of a group of (possible) species.
We can presume the Torosaurus is a further evolutionary stage than Tricerapatops, but by how much? How likely is it that any two (presumably) distinct specimens would have walked together on the Earth? What is the quality of our sample size and why do we value the current assumption over the newer assumptions? Are there any solid guesses on the role distance between two fossils plays on the likelihood of them having shared a habitat?
