... these morphological differences are and should be the very essence and basis for any assessment in taxonomy and morphology of species and species description.
Except that they in some cases are made on an questionable basis. A basic example: I have 20 normal specimens of some species. I find one specimen that looks quite different, e.g. different cranial measurements and alike. I claim it is a new species. This has happened repeatedly in the last decade. Let's imagine this example in humans: I have 20 human specimens. Chance is, they all look pretty normal. I now find a specimen that is clearly different: Shorter stature, proportionally shorter limbs, differences in cranium. Clearly, with such striking difference compared to the 20 'normal' specimens, it must be a new species. Except, of course, the previously described aberrancies are typical of achondroplasia (the most common syndrome that causes human dwarfism), but how would I know with such a relatively simple analysis? Such discrepancies can easily be proven/disproven by adding more methods, e.g. DNA, voice (important in gibbons) or similar. A comparable problem is sampling from extremes. If we imagine a population with range that is approximately 1000 km long, and we only use samples from the two extreme ends of the distribution, how would we know these aren't extremes of a cline rather clear species? We need data in between. Yet another potentialy problematic is the use of microsatellite DNA alone, without more standard DNA analyses. Microsatellite data can be very useful, but it can also give rather misleading results. Although no modern human 'race' is monophyletic (meaning that virtually all serious authorities totally disregard the concept of several modern races in humans), there are some differences in microsatellite DNA that roughly match the 'races'. All this can be summed down to the standard sentence:
Extraordinary claims require extraordinary evidence
Van Roosmalen, easily one of the most knowledgeable people on Amazonian mammalogy, has made some rather remarkable claims (manatee, peccary, tapir, coati, jaguar, etc) supported by little evidence. This has resulted in hesitation (to use diplomatic wording) among other authorities on mammals. It is far harder to criticize his earlier work which has been accepted without hesitation by other authorities. Regarding the recent Ungulate Taxonomy, Groves and the late Grubb should be applauded for this exceptional work, but there also are a number of shortcomings, some of which match what I described above. In fairness, some (but not all) of these studies aren't theirs, but they still quote them as basis for their opinions. I do however find it interesting how people using much of the same basis sometimes come to quite different conclusions. For example, Cotterill, an authority on African ungulates who also is an opponent of bsc, in some cases came to different conclusions when he reviewed African dwarf antelopes, incl. duikers. This can be partially explained by timing (newer studies were not available to Cotterill), but in other cases largely the same evidence was available to Cotterill and Groves+Grubb. Who is right when there is disagreement? I guess time will tell. To their credit, both publications highlight that their suggested classifications are preliminary because many unresolved issues remain.
The very basis for science is that when someone makes a claim, other can question the results. To suggest that any authority is above critisism is highly problematic. I've had people question results in publications I was involved in. This has resulted in the publication of additional support of the original thesis, or the realization that it was wrong. Either way, people questioning results is one of the primary driving forces in science.
As for the white rhino, it is reasonably clear: Either you follow bsc and there is only one species based on published evidence, or you follow psc and there are two based on published evidence.
Finally, I really do wish people working in mammal taxonomy would follow the lead of some other fields (birds, butterflies, fungi, etc) and realize that from a scientific point of view, descriptions like 'a bit darker' or 'deep brown' are useless. Their accuracy depend on the human eye and individual judgement, and therefore can't be tested rigorously in a scientific way. If they instead use color charts (like Naturalist's Color Guide by Smithe) or electronic color measuring systems, it can easily be tested.
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all the splitters and their claims and I need to do a little more reading/research (so little time, so much to read).
