White rhino c.2001

devilfish said:

Does anyone know any definitive characteristics to differentiate the two subspecies of white rhino? (I\'m unconvinced about using hairiness of ears)

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Northern and Southern white rhinos are clearly different in appearance and can be differentiated on all of their measurable components, including tooth measurements, skull lengths, widths and depths, and limb bone lengths. Southern white rhinos are, on average, larger, with adult males weighing 2000-2400 kg, compared to 1400-1600 kg for adult male Northern white rhinos. One interesting point that stands out from the article is that height and length measurements of white rhinos are not abundant at all (to put it mildly). Ok, maybe it’s not a surprise that live rhinos have been measured relatively infrequently, but it’s always worth noting how little data often exists on living animals. White rhinos of both taxa have shoulder heights of about 1.6 m – they’re huge. While the data on height and length isn’t great, Groves et al. (2010) note their impression that Northern white rhinos are taller than Southern white rhinos, and that Southern white rhinos seem to be longer-bodied.

Among the other differences, some stand out as easy to spot. Northern white rhinos have a rather straight back while the dorsal profile of the Southern white rhino is obviously concave and the shoulder hump is more prominent. In the southern form, the palate ends at a point that is approximately level with the junction between the second and third molars, while it ends level with the mid-point of the second molar in the northern form. Northern white rhinos have teeth that are proportionally smaller than those of southern rhinos, and their teeth are also lower-crowned. The two taxa also differ in skull profile. The dorsal margin of the white rhino skull is concave when the skull is seen from the side, but the degree of concavity differs quite strikingly between northern and southern rhinos: the dorsal surface of a northern skull is nearly flat, while that of a southern one is deeply concave (Groves et al. 2010) [the adjacent image, from Groves et al. (2010), shows Southern C. simum above and Northern C. cottoni below].

Various integumentary differences – concerning skin folds and hairiness – might also help distinguish the two rhinos, but they’re variable and (in my opinion) not altogether convincing. Southern white rhinos sometimes have distinct vertical grooves in between their ribs, while northern ones generally don’t, and the skin folds around the top of the foreleg are supposedly more prominent in southern rhinos. Southern white rhinos are also supposed to be hairier on the body, while Northern white rhinos have hairier ears and tails than Southern white rhinos according to some (Groves et al. 2010). These differences are not newly recognised: the two white rhino taxa have always been regarded as obviously distinct (Groves 1972).

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Chlidonias said:

I'm not sure how much help it will be because a lot of the differences are via measurements and I gather much of the external stuff (e.g. hairiness) is open to opinion, but Darren Naish did a bit about them on Tetrapod Zoology in 2010 (with regards to Groves' splitting of them). I bolded the bits about external factors.

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