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Reading technical papers (pdf) is like going to the dentist you would rather not do it but you may get something out of it and I'll try one every once and a while. Here is an interesting one that discusses the two Triceratops described in the Hell Creek Formation Triceratops horridus and Triceratops prorsus. The main authors of this paper are pretty well recognized Ceratopsian experts. The two species are basically identical and the only known differences are variations in cranial features like the length of the postorbital and nasal horns. This paper suggest that the long held hypothesis that the differences are just sexual or ontogenetic variations is not valid and is primarily an evolutionary transformation. In the attached figure they placed all known skulls stratigraphically across the entire Hell Creek Formation and found that T. horridus "features" were found only in the lower Hell Creek (L3) while the upper Hell Creek (U3)contained "features" of T. prorsus. The middle Hell Creek (M3) was a transitional zone. This transformation occurred in a relatively short period of time 1-2 million years and it's difficult to argue against sound evidence. The paper again supports the need to have good information on where your specimen comes from. To get a proper species identification it may not only be necessary to know the formation but specific locality. Paper pnas.201313334.pdf FYI ...R. Boessenecker (aka Boesse) was acknowledged in this paper Next we need to settle the debate around Triceratops and Torosaurus .