Tetrapod Zoology

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It’s official: there’s a new, living species of African rhino, bringing the recognised number of living rhino species to six.

But before you get too excited I should point out that the taxon concerned is not exactly new. It was first named in 1908 and has previously been regarded (without exception) as a ‘subspecies’.

It’s the Northern or Cotton’s white rhinoceros (aka Grass rhino or Square-lipped rhino) Ceratotherium cottoni [captive individual shown above; photo by Jan Robovsky, from Groves et al. (2010)], previously classified as Ceratotherium simum cottoni, and first named by Richard Lydekker following its discovery in 1900* (surprisingly recently for such a large, terrestrial mammal**). In a new paper published in PLoS ONE, Colin Groves and colleagues argue that northern and southern white rhinos differ substantially in morphology and genetics, and should hence be recognised as separate species. As discussed below, this has implications for the conservation priority of the critically endangered Northern white rhino population [map below, from wikipedia, shows historical distribution of the two Ceratotherium taxa. C. cottoni's range is shown in orange and C. simum's in green].

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* Percy H. G. Powell-Cotton was the first person to bring Northern white rhinos to scientific attention: in 1900 he collected a specimen from the Lado District of South Sudan. Oldfield Thomas published on these discoveries in 1900, but it was Lydekker (1908) – well known for being a consummate splitter, though don’t let that put you off – who made the decision to name the northern rhino as a new subspecies. Lydekker used the name Rhinoceros simum cottoni: the generic name Ceratotherium had been coined by Gray in 1868, but the taxonomy of African rhinos was confused at this time (Rookmaaker 2005a).

** Note that it’s far from being the most recently named living rhino: there are also the recently named supposed subspecies Rhinoceros unicornis sinensis Laufer, 1914, Diceros bicornis occidentalis Zukowsky, 1922, C. s. scotti Hopwood, 1926, C. s. efficax Dietrich, 1945, Dicerorhinus sumatrensis eugenei Sody, 1946, Diceros b. palustris Benzon, 1947, Diceros b. punyana Potter, 1947, Diceros b. longipes Zukowsky, 1949, R. u. kagavena Deraniyagala, 1958, Diceros b. michaeli Zukowsky, 1964, Diceros b. angolensis Zukowsky, 1965, Diceros b. atbarensis Zukowsky, 1965, Diceros b. chobiensis Zukowsky, 1965, Diceros b. ladoensis Zukowsky, 1965, Diceros b. nyasae Zukowsky, 1965, Diceros b. rendilis Zukowsky, 1965, Diceros b. rowumae Zukowsky, 1965, Dicerorhinus s. harrissoni Groves, 1965, R. u. bengalensis Kourist, 1970 and R. u. barinagalensis Srivastava & Verma, 1972. However – the majority of these proposed taxa have not stood the test of time, or are considered of dubious validity (e.g., Rookmaaker 2005b).

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.

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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).

Groves et al. (2010) reviewed genetic data as well, and this also shows that Northern and Southern white rhinos are highly distinct. The level of divergence observed between analysed segments of DNA is high, and a separation date of about 1 million years is hypothesised [two C. simum individuals from Namibia shown below; from wikipedia].

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So, the two white rhino taxa are morphologically and genetically distinct, and have been separate for about a million years. It’s well known that Groves is a proponent of the phylogenetic species concept (or PSC), and – by applying this concept to the two taxa – Groves et al. (2010) conclude that “we have no option but to consider them specifically distinct” (p. 12). It will be interesting to see whether this proposal is accepted: it’s inevitable and predictable that some people will regard this act as an unwarranted taxonomic splitting. The proposal means that white rhinos join the long list of extant mega-mammal taxa where the ‘subspecies’ of tradition have recently been elevated to specific status: you might remember that we looked at this subject very recently in Laissez-faire lumping under fire.

Brief distraction from Killer whales

You may have heard that a new study (Morin et al. 2010) has also supported the idea that Orcinus orca should be split up into several distinct species: this is not a new idea, as the genetic and morphological differences observed between resident, transient and Antarctic orcas have long led some experts to make these sorts of suggestions (e.g., Berzin & Vladimirov 1983, LeDuc et al. 2008). Indeed, two additional species – O. nanus Mikhalev et al., 1981* and O. glacialis Berzin & Vladimirov, 1983 – were named in the 1980s.

* No type specimen was allocated, making O. nanus a nomen nudum.

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Back to the rhinos… one argument that could (and will) be used to support the new taxonomy is that it should help bring attention to the Northern white rhino as an entity desperately in need of conservation priority. The Northern white rhino now seems extinct in the wild (the remaining handful of individuals – those in Garamba National Park in Democratic Republic of the Congo – seem to have died prior to 2003), and captive breeding could well bring the taxon back from the brink (as it has with Southern white rhinos). As is well known, ‘species’ get more attention than ‘subspecies’ [captive C. simum shown here; photo by Eric Harty, from wikipedia].

The danger in making this sort of suggestion, however, is that changing the taxonomy to suit conservation priority could eventually backfire: it would not look good if zoologists were thought to be tweaking their conclusions in order to suit their favoured conservation projects.

Having said all that, Groves et al. (2010) have done a good job of emphasising the point that the two white rhino taxa really are highly distinct, and have been so for a very long time. In fact, one might argue that the recognition of the Northern white rhino as a distinct species is probably long overdue, and some rhino experts are already saying exactly this.

More neat perissodactyl news is due very soon! If you’re interested in rhinos, be sure to check out the amazing resource that is the Rhino Resource Center [captive C. simum show below; photo by Dick Mudde, from wikipedia].

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And for previous Tet Zoo articles on rhinos see…

Stuffed megamammal week, day 4: Sumatran rhino
How did the White rhino get its name? Not how you think (even if you’re very clever)
Chinese black rhinos and deinotheres, giant sengis, and yet more new lemurs
Tet Zoo picture of the day # 5 (on Ceratotherium and the 2007 Rhino May Day event)
Tet Zoo picture of the day # 3 (on Elasmotherium)
War rhinos

And if newly recognised species and taxonomic reshuffling interests you, check out…

Refs – -

Berzin, A. A. & Vladimirov, V. L. 1983. Novyi vid kosatki (Cetacea, Delphinidae) iz vod Antarktiki. Zool. Zh. 62, 287-95. ['A new species of killer whale (Cetacea, Delphinidae) from Antarctic waters'].

Groves, C. P. 1972. Ceratotherium simum. Mammalian Species 8, 1-6.

Groves CP, Fernando P, & Robovský J (2010). The sixth rhino: a taxonomic re-assessment of the critically endangered northern white rhinoceros. PloS one, 5 (4) PMID: 20383328

LeDuc, R. G., Robertson, K. M. Pitman, R. L. 2008. Mitochondrial sequence divergence among Antarctic killer whale ecotypes is consistent with multiple species. Biology Letters 4, 426-429.

Lydekker, R. 1908. The white rhinoceros. Field 22nd February 1908, 319.

Morin, P. A., Archer, F. I., Foote, A. D., Vilstrup, J., Allen, E. E., Wade, P., Durban, J., Parsons, K., Pitman, R., Li, L., Buffard, P., Nielsen, S. C. A., Rasmussen, M., Willerslev, E., Gilbert, M. T. P. & Harkins, T. 2010. Complete mitochondrial genome phylogeographic analysis of killer whales (Orcinus orca) indicates multiple species. Genome Research [Epub ahead of print] doi: 10.1101/gr.102954.109

Rookmaaker, L. C. 2005a. Review of the European perception of the African rhinoceros. Journal of Zoology 265, 365-376.

- . 2005b. The Black rhino needs a taxonomic revision for sound conservation. International Zoo News 52, 280-282

Comments

#1 Hai~Ren
May 3, 2010

Interesting news.

I sure hope the formerly captive Northern white rhinoceros that have been sent to Kenya start reproducing soon, and help to boost the numbers of this seriously critically endangered species. I know that there are Southern white rhinoceros in some Kenyan parks – are these in a sense non-native? I’m wondering if the historic range of either of the white rhinoceros species is a vestige of a formerly much more widespread distribution which would have included Kenya.

Makes me wonder about the possibility of other rhinoceros species being split off, especially those that are geographically isolated – the Borneo subspecies of the Sumatran rhinoceros comes to mind.

Then there’s also the Javan rhinoceros populations in mainland Asia, although it is now restricted to a tiny handful in Vietnam. I wonder if the also extinct Sumatran population of Javan rhinoceros might have been sufficiently distinct to be split off as a subspecies.
#2 WhiteJenna
May 3, 2010

Will be printing this out for the zoo kitchen bulletin board and telling our two Southern boys about the family reshuffling.
#3 AnJaCo
May 3, 2010

Anybody know how many Northern White rhinos exist? Enough to reconstitute a not-too-inbred population?
#4 Jaime A. Headden
May 3, 2010

It should be noted that the authors assert for their purposes that their criteria for distinguishing these two taxa as species and not subspecies is very, very short:

From Groves et al. “Under the Phylogenetic Species Concept (the only objective concept applicable to allopatric forms), we have no option but to consider them specifically distinct.”

However, the authors are also seemingly driven by the idea that conservation status of the northern versus the southern taxon has lagged, and this may actually influence the above argument. They state:

“The taxonomic status of the Northern form is central to determining its conservation importance and will be a critical driver of efforts to save it.”

It seems supporting specific status under a defunct Linnaean concept is the only way to force recognition of said taxon; it also consequently aids the conservation status of simum as it in one swoop reduces the range and number of animals for both groups, creating a fairly historic “break” in size of the two groups.

Otherwise, recognition of the level of difference between the two taxa has increased, but the fact of the difference between them has NOT, as they have been regarded as separate for over 100 years.
#5 Albertonykus
May 3, 2010

Way cool. More Lassez Faire lumping terminated.
#6 Hai~Ren
May 3, 2010

AnJaCo: Barring any surviving individuals in Garamba National Park in the north-east Democratic Republic of Congo (last count was four in 2005) or Sudan, we are now down to EIGHT living northern white rhino.

Four of them (2 males, 2 females) were recently transferred from Dvur Králové Zoo in the Czech Republic to the Ol Pejeta Conservancy in Kenya. A pair of females remain at the zoo, one that is elderly and another that is incapable of reproducing. Similarly, a male and a female are at the San Diego Wild Animal Park, but both are apparently not going to reproduce anytime soon as well.

There is a hybrid between the northern white rhino and southern white rhino (southern father, northern mother), born at Dvur Králové in 1977, but died in 2007.
#7 Jaime A. Headden
May 4, 2010

Albertonykus wrote:

Way cool. More Lassez Faire lumping terminated.

That’s not a good example of laissez faire lumping; what you want is something more like what happened with Troodon formosus.

Phil Currie, bless is heart, started a trend that eventually resulted in the compounded os an assortment of taxa (some which may be very different) which derive from southern Canada to central US and from the Campanian to the Maastrichtian into one species. This is still followed today, especially by Dave Varricchio, Julia Sankey, etc., who also regard any tooth of a troodontid morphology gets the formosus label. Troodon and formosus are — if one regards them separately as it seems many do — wastebasket taxa, and includes:

Stenonychosaurus inequalis (skeletal material)
Polyodontosaurus grandis (partial skeletal and dental material)
Pectinodon bakkeri (dental material)
Paronychodon sp. (in part)
Richardoestesia sp. (in part)
Aublysodon sp. (in part) (we assume)

Most of the referral occurs by the basic assumption (currently being promoted by dino-lumper Jack Horner) that taxa are oversplit in today’s world, over-recognized splitting is occuring with almost any given trait, and that lumping is safer because the taxa can always be split later. This doesn’t help with taxa that are lumped after the fact, but for the most part modern subspecies are generally named as such at the time … which makes them inapplicable to the verb “lump.”
#8 RaMa
May 4, 2010

There are apparently no Rhinos in Garamba anymore! See this article on TimesOnline.

@Darren: The lack of a holotype would not have made Orcinus nanus a nomen nudum in 1981. Even a very poor description makes a name available, and a neotype designation could bring this name back into play again.

Rainer
#9 Mark Lees
May 4, 2010

Im not happy with the idea of conservation driving taxonomic/systematic decisions. But in this case there does seem at least a decent case for for recognising them as separate species.
I note that White Rhinos (southern) are shown as occuring in Zambia on the map. I am told this is no longer so. In 2004 I visited the nat park where the last three lived. It was amazing being able to get close to them on foot (following the 5 metre rule – i.e. don’t sneak up on them and don’t get closer than 5m). Unfortunately I read they have been poached and are now all gone. Can anyone confirm this?
#10 Erior
May 4, 2010

Mmm, so, 6 species, 4 genus, evenly distributed between Asia and Africa… Heh, looks neat for a collectionist…

The sad thing is that probably we will end up with 4 monotypic genus in a short time, and not due to lumping, precissely. Maybe even just 3 genus… yeah.

And, while I am a bit of a lumper, those differences seem acceptable to erect species (not genus). I’m not quite convinced of African buffalo and elephant not being just one species each, due to the whole “open ring” issue, but these ones are insolated and show differences. Good enough for me.
#11 Jerzy
May 4, 2010

Wow, very controversial issue.

1. Northern white rhino indeed numbers 8 old captive individuals, and all females might be too old to breed. Zoo Dvur Kralove moved it’s four possible breeders to Kenya. There is a rumour that a pair with calf was seen from the air by pilots overflying south Sudan. There are apparently some attempts to verify this record on the ground, but no results. This may be just a rumour.

The last individuals at Garamba NP in DRC are dead. It is especially said that Congolese government blocked the attempt to evacuate these rhinos to Kenya in early 2000s, calling that they “will protect them in their country”. So they did. Most stupid case of national pride. :/.

2. I doubt if in case of northern white rhino, the
split will give the expected benefits for conservation. The situation at Garamba was well known before. The article came too late to have any effect on protection.

The split may actually harm rhino conservation. There is a talk that introducing southern white rhino females to Ol Pejeta may be the only option, to preserve part of genetic material in hybrid animals, or to increase the social group – white rhinos breed better in herds. With the proposition of two different species, this is more difficult.

Also, many southern white rhinos live in E African reserves, partially introduced as more visible species to boost tourist revenue to conserve black rhino. Now they might be seen as exotics.

3. Am I the only one who sees that morphological differences between N and S white rhinos are simply trivial? Especially size is totally bogus, because big mammals are so prone to variation in size because of nutrition, locality etc.

4. Southern white rhino is itself inbred. All animals come from a
small group which survived in early 20. century hunters in one South
African locality. The paper doesn’t adress that. So any differences may be result of simply local/individual variation locked by inbreeding.

5. White rhino was prehistorically widely distributed in Africa. Curiously, I heard that the gap between subspecies is itself an artifact, a relic of hunting by native Africans. Apparently, both races live in areas where people are more cattle herders not hunters.
#12 Dave Hughes
May 4, 2010

I agree with Jerzy, the cited morphological differences sound like small potatoes to me. A skin fold here, a few more hairs there – big deal. I’m sure we could all think of many examples of mammals which show as many, or greater physical differences over a comparable geographical distance, and yet are comfortably regarded as single species. Dare one say it, even Homo sapiens probably falls into this category.

Whether we call the northern rhino a distinct species or not should have no bearing on its conservation importance. We should do our best to save it because it’s there, not because of the label we choose to give it. And if we do decide that it really is a separate rhino species, then unfortunately we will probably soon be mourning its extinction, as it sounds as though the remaining remnant population is far too small to recover without help from its southern cousins.
#13 Darren Naish
May 4, 2010

Thanks for very interesting comments. With regard to comments 11 and 12, I will definitely agree on this case that the morphological differences reported to distinguish the two taxa are, indeed, extremely trivial, and while writing the article I did wonder if I’d be able to distinguish the two rhino if confronted with them in the field. I think this is quite different from such ‘un-lumped’ mega-mammals as orangutans, African elephants, African buffalos and so on. So, I agree that scepticism is warranted here.

However, if anything’s become clear from the debate on ‘cryptic species’, it’s that we need both a molecular and a morphological perspective in order to be informed. Genetic studies indicate that the two Ceratotherium taxa diverged somewhere between 750,000 yrs and 1.5 million yrs ago… but here we come back to the problem of what a species is anyway, and it’s entirely conceivable that a mammal species might persist for a couple million years at least.

I admit that I don’t know what to do, and I see the merits of both arguments (that is, ‘for’ and ‘against’ species status for cottoni). I’ve seen a few opinions expressed by rhino experts (notably Kees Rookmaaker), but would love to know of more thoughts from the rhino research community. Actually, there was a round-table discussion about the subject at a recent rhino conference, and distinct ecological differences between the two taxa were mentioned (I think by R. N. Owen-Smith).
#14 Andreas Johansson
May 4, 2010

75k to 1.5M years? That sounds like a very big error bar. Or is the first number to be supposed to be 750k?
#15 Darren Naish
May 4, 2010

It is, oops. I do not do numbers. Will go correct.
#16 Sili
May 4, 2010

Great. One more species to watch go extinct.
#17 Jim Thomerson
May 4, 2010

Meant to be helpful comment–the plural of genus is genera. It does seem to me that commenting on conservation status in a species description may not be the best course. Species description is science in its purest truth-seeking form. Conservation is, and must be, political. Basically get two publications out of it instead of just one.
#18 Coturnix
May 4, 2010

I wish this post (and other similar posts) were aggregated at ResearchBlogging.org.
#19 Dartian
May 5, 2010

Dave (and Jerzy):

I agree with Jerzy, the cited morphological differences sound like small potatoes to me. A skin fold here, a few more hairs there – big deal.

That’s a misrepresentation of what the authors say. Groves et al. devote precious little space for discussing external differences between these two rhino taxa; in fact, they even explicitly say that, in their opinion, most external characters are ‘too variable for being diagnostic’. The bulk of their paper consists of biometrical analyses of skeletal (mostly dental and cranial) characters. It is the taxonomic relevance of those characters, and of the genetic data, that you need to address if you wish to dispute the specific status of Ceratotherium cottoni.
#20 Jaime A. Headden
May 5, 2010

Dartian,

It is not the specific status of cottoni that is at issue: It is the difference between having two extant species of Ceratotherium versus one extant species of Ceratotherium with two extant subspecies. As I pointed out, the authors use the distinguishing effect of the Phylogenetic Species Concept (PSC) to argue that the taxa represented are real; it is conservation that seems the relevant force to push the subspecies up to species “rank.”
#21 Dartian
May 5, 2010

Jaime, I took no position on the issue whether the two rhino taxa should be treated as species or as subspecies (I’m on the fence myself regarding this). I only pointed out that any objections to Groves et als.’ position should be based on what the authors actually said in the paper.
#22 Andreas Johansson
May 5, 2010

Jaime wrote:

It is not the specific status of cottoni that is at issue: It is the difference between having two extant species of Ceratotherium versus one extant species of Ceratotherium with two extant subspecies.

Hm? How are those two not the same?
#23 Darren Naish
May 5, 2010

Coturnix (comment 18): a lot of people say I should announce my articles at Research Blogging. Alas, I am more of a dumbass than most people know: I have not found Research Blogging at all user friendly and gave up after failing to get it to do what I wanted. If anyone can talk me through it – and deal with me as if I’m a very unintelligent 6 year old – I’ll give it another go.
#24 Dartian
May 5, 2010

Darren:

I did wonder if I’d be able to distinguish the two rhino if confronted with them in the field

I, for my part, am not sure if I could ever tell apart a willow warbler from a chiffchaff in the field with any certainty*. But that doesn’t mean that I think they should be lumped together in one species. There are much, much more ornithologically knowledgeable people than me out there who can tell apart a willow warbler from a chiffchaff in the field (or, to be precise, I am confident beyond any reasonable doubt that they can), even if I personally can’t.

* Yeah, they sing differently, but who has established that differences in vocalisation are a more objectively reliable way of telling apart bird species than differences in dentition are of telling apart mammal species? And besides, how do we know that northern and southern white rhinos do not, for example, differ regarding their body odour every bit as clearly as willow warblers and chiffchaffs differ regarding their vocalisations?

I’m not trying to be snarky, I’m just trying to point out that the all-too-easily (and sometimes unwittingly) made argument from personal incredulity won’t get us very far in discussions about proper species delimitations.
#25 Darren Naish
May 5, 2010

Not to be argumentative, but chiffchaff and willow warbler are actually pretty easy to tell apart once you know how to do it (they have different coloured legs, for one thing). Plus, unlike the two white rhinos, they’re not sister-taxa, but are actually pretty distant in leaf warbler phylogenies. However, your general point is made.
#26 Dartian
May 5, 2010

Darren:

chiffchaff and willow warbler are actually pretty easy to tell apart once you know how to do it

Off-topic, but… Have you already gotten yourself a copy of the second edition of the Collins Bird Guide? What’s your opinion of it, especially regarding the authors’ taxonomic decisions, and dare we expect a review (written from the unique Tet Zoo perspective, of course)?
#27 Mark Lees
May 5, 2010

With experience telling chiffchaff and willow warbler apart can be very difficult or fairly straightforward depending on the time of the year and moult stage.

Also telling apart some of the split chiffchaff forms can be not too bad given a good view and the right stage of moult. Though there are always some individuals that prove a challenge.

Very often telling apart morphologically similar species becomes significantly easier when you are familiar with what is normal for a form and ideally with its range of variation. So often what starts out being ‘they all look the same’ becomes ‘but they are obviously different’. I found this with many gulls, and also with warblers. Its often not single things, but rather combinations of characters, including behavioural ones. So taken separately things like a slightly darker colour, slightly different size, more upright stance, etc seem trivial, taken together they can create a quite distinct effect.

I have the 2nd edition Collins Bird Guide, I mostly like it, though feel they could have done so much more. As for the taxonomic decisions, they seemed a bit conservative to me.
#28 David Marjanović
May 5, 2010

Species description is science in its purest truth-seeking form.

This is about as wrong as it can be.

That’s because there isn’t a single definition of “species”. There are, as of February 2008, no less than 147 of them, and they all lead to different results. For instance, depending on the definition, there are from 101 to 249 endemic bird species in Mexico.

Groves et al. (2010) have the good sense of making explicit which definition they use. Under the Phylogenetic Species Concept, the northern and the southern white rhino are indeed separate species. Under at least one of the Biological Species Concept they are not (they can interbreed, and the hybrids are fertile, right?), and under a Morphological Species Concept they might not be (though Groves et al. nonetheless try to offer morphological criteria for distinguishing their two PSC-species).

AFAIK, there is no objective way of preferring one species concept over the 146 others. That’s why there are so many, and that’s why they aren’t going away.

Really, the word “species” should be abandoned, and the entities described by each species concept should get separate names. Perhaps even separate nomenclatures (though that would be very confusing in practice).
#29 Jerzy
May 5, 2010

#19
The separation of 750,000-1,5mln ya is inferred from genetic difference of ca. 1%, by rather shaky assumtion that genetic distance accumulated evenly since separation of Diceros from Ceratorheium.

Similar genetic distance and estimated divergence times are not unknown within accepted mammalian species. The collared peccary and yes, humble domestic cow come to mind.

#26
Collins bird guide is not a taxonomic reference. Authors follow recent recommendations of BOU. These you should consult and discuss. They are all online here: http://www.bou.org.uk/recTSC.html
#30 Jerzy
May 5, 2010

#28
I think it will be the other way round. Taxonomists make some own code of taxonomic rank and stop messing with names which everybody uses.

There is now interesting article in The Economist about a proposition to rename Drosophila melanogaster put by some insect taxonomist. And what genetics world politely said.

99% of biologists study creatures genetics, ecology or behaviour. Stability of the name far more important to them then who is animals closest vs. second-closest relative.
#31 Darren Naish
May 5, 2010

One comment on hybrids: there’s only one recorded Northern x Southern hybrid – a female called Nasi, born in 1977 at Dvůr Králové Zoo in the Czech Republic and euthanised in 2007. “Nasi’s health seemed poor considering her age; we are unsure whether to attach any significance to this, but five older individuals (pure-bred Northern) are still living, born in 1972, 1973 and 1974″ (Groves et al. 2010, p. 11). I just learnt of some interesting comments on the Northern white rhino situation on Retrieverman’s Weblog here.

And, nope, I haven’t seen the new Collins bird guide.
#32 Hai~Ren
May 5, 2010

You can check on the progress of the 4 northern white rhino that have been moved from Dvur Králové Zoo to the Ol Pejeta Conservancy in Kenya at this link.
#33 Jim Thomerson
May 5, 2010

That two species can produce fertile hybrids in the lab is not conclusive evidence that they are the same species. Although it does make one wonder. Even occasional fertile hybrids in the wild is not conclusive. The question is; how much introgression is occurring? Look at the literature on Fundulus notatus and Fundulus olivaceous for example.

When we revised Austrofundulus in 1978, we recognized two species, one with several somewhat distinctive local populations. We discussed and described them but did not think they merited subspecific rank. In 2005 we again revised Austrofundulus, with the help of DNA data, and recognized seven species. It amuses me how different the local populations look to me now that I know they are separate species.
#34 Dave Munger
May 5, 2010

Darren,

We’d love to have your posts collected on ResearchBlogging.org. I see that your old account is still active. Send me an email at dsmunger@gmail.com if you have any questions about how to start collecting your posts there.

Dave
#35 doug l
May 5, 2010

It’d be a good idea to establish a few populations in areas that once had rhinos but now dont and are distant from their modern natural range, just in case some sort of regional extinction happens. The american southwest…bring back some of that old pleistocene religion.
#36 Dartian
May 6, 2010

Jerzy:

Collins bird guide is not a taxonomic reference.

No, of course it isn’t, but the authors still had to choose whose taxonomical recommendations to follow.

Authors follow recent recommendations of BOU.

Are you sure about that? Of the CBG’s surviving authors/illustrators, Lars Svensson and Dan Zetterström are Swedish while Killian Mullarney is Irish – why would they be following the recommendations of the British Ornithologists’ Union? I was under the impression that, being the multi-national effort that it is, the CBG-2 is using some kind of compromise taxonomy. (Disclaimer: I have thus far only had a casual look at the 2nd edition, so I don’t know exactly which controversial taxa the authors recognise and which they do not.)
#37 Dartian
May 6, 2010

Doug:

It’d be a good idea to establish a few populations in areas that once had rhinos but now dont and are distant from their modern natural range, just in case some sort of regional extinction happens. The american southwest…bring back some of that old pleistocene religion.

Not that it matters much to the point you were making, but there were no rhinos in Pleistocene North America. The last NA rhinos, which were quite different from the extant species, went extinct in the early Pliocene.
#38 Jaime A. Headden
May 6, 2010

Andreas Johansson wrote:

“Hm? How are those two not the same?”

That’s my point. (They are technically different when using certain proscribed systems, such as the Linnaean ranking system, but that’s also my point.)

I think David has the right of it, and I am gravitating towards a system in which even species are lost for the sake of simple arbitrary PSC splits of explicit genetic distance. How this works with morphology would require explicit morphological distinction, within the perspective of potential sexual dimorphism.

Under these criteria, ring species and hybrids would be reclassed as “species” with unique nomenclature. They would all involve uninomials. But that’s an extreme of an idea, and I doubt it will take hold for some time; it makes explicit arguments of boundaries and comparativeness that are much less subjective than the current methods.
#39 Andreas Johansson
May 6, 2010

Jaime wrote:

That’s my point. (They are technically different when using certain proscribed systems, such as the Linnaean ranking system, but that’s also my point.)

How are they technically different? I fail to see how the two issues can be different under any system.
#40 David Marjanović
May 6, 2010

[from Darren: sorry, delayed as spam]

There is now interesting article in The Economist about a proposition to rename Drosophila melanogaster put by some insect taxonomist.

It’s not a proposal.

Here is the petition to the ICZN to change the type species of Drosophila from D. (D.) funebris to the very distantly related D. (Sophophora) melanogaster…

…and here is its rejection.

So, either:

– Drosophila keeps its upwards of 1,450 (one thousand four hundred fifty) species and stays quadruply paraphyletic,
– or we lump its descendants (several hundred more species) into it,
– or we split it into clades;

in the latter case, we get Sophophora melanogaster.

This has been commented here and here. (Amazingly, the second is not behind a paywall! Read the comments to it, too.)

99% of biologists study creatures genetics, ecology or behaviour. Stability of the name far more important to them then who is animals closest vs. second-closest relative.

But… it’s not good when a name is actively misleading about the relationships. “Nothing in biology makes sense except in the light of evolution” (Dobzhansky), “nothing in evolution makes sense without a good phylogeny” (G. C. Gould & B. MacFadden).

It’s a big disadvantage of the binominal system that it puts relationships into names.

That two species can produce fertile hybrids in the lab is not conclusive evidence that they are the same species.

Under one species concept, it is proof that they are the same species, because it’s the one and only criterion under that particular concept (one of the two Biological Species Concepts).

Under the other 146, it’s completely irrelevant.

It amuses me how different the local populations look to me now that I know they are separate species.

You don’t know any such thing. You changed your preference of species concept, and you discovered new data to which species concepts can be applied.
#41 David Marjanović
May 6, 2010

WTF. I can’t even have four links in the same comment!?! Submitted again in two parts:

There is now interesting article in The Economist about a proposition to rename Drosophila melanogaster put by some insect taxonomist.

It’s not a proposal.

Here is the petition to the ICZN to change the type species of Drosophila from D. (D.) funebris to the very distantly related D. (Sophophora) melanogaster…

…and here is its rejection.
#42 David Marjanović
May 6, 2010

So, either:

– Drosophila keeps its upwards of 1,450 (one thousand four hundred fifty) species and stays quadruply paraphyletic,
– or we lump its descendants (several hundred more species) into it, creating an even less manageable genus(remember that the ICZN allows only two ranks between genus and species),
– or we split it into clades;

in the third case, we get Sophophora melanogaster.

This has been commented here and here. (Amazingly, the second is not behind a paywall! Read the comments to it, too.)

99% of biologists study creatures genetics, ecology or behaviour. Stability of the name far more important to them then who is animals closest vs. second-closest relative.

But… it’s not good when a name is actively misleading about the relationships. “Nothing in biology makes sense except in the light of evolution” (Dobzhansky), “nothing in evolution makes sense without a good phylogeny” (G. C. Gould & B. MacFadden).

It’s a big disadvantage of the binominal system that it puts relationships into names.

That two species can produce fertile hybrids in the lab is not conclusive evidence that they are the same species.

Under one species concept, it is proof that they are the same species, because it’s the one and only criterion under that particular concept (one of the two Biological Species Concepts).

Under the other 146, it’s completely irrelevant.

It amuses me how different the local populations look to me now that I know they are separate species.

You don’t know any such thing. You changed your preference of species concept, and you discovered new data to which species concepts can be applied.
#43 Morgan Churchill
May 6, 2010

I have the new Collins guide and can certify it doesn’t strictly follow BOU classification. For instance there are new splits of some taxa that are outside of the BOU jurisdiction. Obviously, a field guide couldn’t cover all of Europe and solely base their taxonomy on the BOU.

While the Phylogenetic Species Concepts has some aspects I find troublesome, I do agree with it that recognizing subspecies is not terribly useful, as there seems to be little agreement on what exactly a subspecies is, and when the name should be applied.
#44 Jim Thomerson
May 6, 2010

I haven’t really thought about subspecies since the 1970′s. As I recall there was a calculation to see if any morphological character showed more than 90% non overlap (maybe it was 75%). The geographic distribution needed to be well known and there should be a fairly narrow zone of intergradation. There is an anti spubspecies argument that if you erect subspecies based on the pattern of variation in certain traits, you may be obscuring a different pattern of variation in other traits.

Species are much simpler, it is just a matter of “Gee, I ain’t never seen one of those before!” Just kidding. of course.
#45 Jerzy
May 6, 2010

#36
BOU taxonomic committee became a sort of guru among European birdwatchers. One exception are Dutch who split much more species, but nobody follows them.

They don’t follow, very sensibly, order of species and families, particulary recent reshuffling of paserines. In the field guide it is important that similar species are together, and the user is familiar with the layout and can find the right page before the bird flies away.

Anyway, there are now two different sequences of bird taxonomy in field guides – one in Asia and one elsewhere, and most people complain that they know one but are lost in another. Not good if you have a few second of observation of the moving bird!
#46 Jerzy
May 6, 2010

#40-42
David, read carefully comment of David States at:
http://www.nature.com/news/2010/100407/full/464825a.html
Drosophila name is embedded in biotech patents, reagents and software. I wouldn’t bet much money that it all is going to be rewritten.

99% of Drosophila researchers care only about relationship of Drosophila melanogaster to E.coli, yeast, Arabidopsis, Caenorhabditis, mouse, rat and human. And there is probably more of them than researchers working on all taxonomy together.
#47 Jim Thomerson
May 6, 2010

Bad taxonomy is the root of all evil. Actually a bit of truth in that comment.

There are long established official lists of common and scientific names of fishes. The common names are quite stable.
#48 David Marjanović
May 7, 2010

99% of Drosophila researchers care only about relationship of Drosophila melanogaster to E.coli, yeast, Arabidopsis, Caenorhabditis, mouse, rat and human. And there is probably more of them than researchers working on all taxonomy together.

I know. That’s why I’m rather surprised that the proposal was rejected.

But rejected it was. This leaves the three options I listed.
#49 Jaime A. Headden
May 7, 2010

Andreas Johanssen,

I am not sure we’re talking past one another, but I do there there is a large break in communication here.

Model 1. Ranked systems, original: Ceratotherium (genus) simum (species) simum (subspecies 1); Ceratotherium (genus) simum (species) cottoni (subspecies 2); as an historic entity, the species here is simum, and is itself split into subspecies; The model invests a reality in the position of the rank, such that it has an independant existence from the taxa they are aligned to, as it is mandated (yes, I know the argument I stated is illogical).

Model 2. Ranked systems, PSC argument: Ceratotherium (genus) simum (species); Ceratotherium (genus) cottoni (species); notice that we’re still using ranks.

Model 3. Unranked systems, unargued:
Ceratotherium (clade) simum (species); Ceratotherium (clade) cottoni (species); we’re not using ranks anymore, but the species is a validated entity, while the other taxa are just clades. In the further derivation of this system, they were also be redundant if no split is argued under which the nomenclature is established (two species under one clade, but using the italicization of the “genus”-equivalent taxon).

Groves et al argue for 2, but still would adopt 1; this indicates they are using the Linnaean system. Abandoning the system in all ways would actually lead to a model that is very different, in that ranking leaves us without genera and species (What do we even italicize anymore?!).

Model 2 was done to support cottoni as a species as a conservation movement because apparently in this system, subspecies cannot be conserved on their own, which makes model 1 and model 2 quite different in that C. simum cottoni and C. cottoni are treated as different classes of entities. While they may seem identical in the abstract, in the details they are different.
#50 Tim Morris
May 8, 2010

@ Jaime:

I’ve always considered Pectinodon to be separate from Troodon. But what we need to make sure that Pectinodon is distinct would be a 100% complete troodon dentition to make sure it’s not just heterodonty.
#51 David Marjanović
May 8, 2010

What do we even italicize anymore?!

The PhyloCode recommends italicizing all “scientific names”. I like to interpret this as all clade names with a phylogenetic definition, but it’s by no means clear from the wording; some italicize all rank-based names as well.
#52 Darren Naish
May 8, 2010

I’ve just co-authored an article with Jacques Gauthier and he italicised _all_ formal taxonomic names.
#53 gary johnson
October 18, 2010

we should stand up and not let them go extinct