Ungulate taxonomy revisited: the evidence for the splits of G&G

What Wild Boar taxa is introduced in North America?

 

Likely the nominate, but are the pigs present in North America pure anymore? I thought they'd all be extensively hybridized with feral pigs which results in their sometimes enormous size.

~Thylo

 

And now the remaining Asian pig species

Visayan warty pig

The Visayan warty pig (Sus cebifrons) is a critically endangered pig species originally occuring on Cebu, Negros, Panay, Masbata, Guimaras and Siquijor islands in the Philippines. Two subspecies have been described, cebifrons from Cebu being extinct. The other subspecies negrinus is still extant.

Sus cebrifrons negrinus from Negros

@ro6ca66 , Cotswold Wildlife Park, UK


@demonmoth, Cotswold Wildlife Park, UK

Sus cebifrons negrinus from Panay

@Blackduiker , Saint Louis Zoo, USA


@thor , San Diego Zoo, USA

Sulawesi warty pig

The Sulawesi warty pig (Sus celebensis) is a monotypic pig species endemic to Sulawesi Islands, Indonesia.

No pictures of this species have been uploaded to the gallery

Palawan wild pig

The Palawan wild pig or Palawan bearded pig (Sus ahoenobarbus) was previously included as a subspecies of Bearded pig, but has since been shown to be distinct. This monotypic species is restricted to the Islands of Palawan, Balabac and the Calamian Island group.


@alexkant , Palawan Wildlife Center, Philippines

Bearded pig

The Bearded pig (Sus barbatus) is a large pig species from Peninsular Malaysia, Borneo, Sumatra and nearby islands. Two subspecies have been recognized:

Sus barbatus barbatus Borneo & Peninsular Malaysia
Sus barbatus oi Sumatra, Bangka and Palang Bintang Islands

Sus barbatus barbatus

@LaughingDove , Danum Valley, Malaysia

(with some domestic pig blood)

@ThylacineAlive , Berlin Zoo, Germany

Pygmy hog

The Pygmy hog (Porcula salvania) is the smallest extant pig species. It is the sister species to the genus Sus. It has in recent years been placed in a monotypic genus, but it there has been extensive hybridization with Eurasian wild pig and phylogenetic divergence has been estimated at 2 mya (Liu et al. 2019). In that light it could be included in the Sus genus again. This monotypic species has an extremely limited distribution in Eastern India.


@Chlidonias , Breeding Centre at Nameri NP, India


@Chlidonias , Breeding Centre at Nameri NP, India

 

What happened to the warty pigs from Panay turning out to be different from negrinus? The US population has always been to referred to as non-subspecies because no one has ever been sure what the Panay animals really are other than them being different.

~Thylo

 

And to finish the Suidae family; the remaining African species.

Common warthog

The Common warthog (Phacochoerus africanus) is a widespread pig species, occuring throughout most of sub-saharan Africa. Generally four subspecies are recognized:

P.a. africanus W Africa
P.a. aeliani Eritrea
P.a. massaicus E Africa
P.a. sundevallii S Africa

The existence of africanus, massaicus and sundevallii is backed up with genetic data (Muwanika et al., 2003).

Phacochoerus africanus africanus

@vogelcommando , Safaripark Beekse Bergen, Hilvarenbeek, Netherlands


@KevinVar , Mole NP, Ghana

Phacochoerus africanus massaicus

@Hix , Arusha NP, Tanzania


@Hix , Ngorongoro Crater, Tanzania

Phacochoerus africanus sundevallii

@Maguari , Moremi GR, Botswana

Desert warthog

The Desert warthog (Phacochoerus aethiopicus) is a pig species that now only occurs in arid areas in NE Africa. A second subspecies is now extinct:

P.a. aethiopicus Cape Regions, South Africa (extinct)
P.a. delamerei NE Kenya, Somalia, E Ethiopia

Phacochoerus aethiopicus delamerei

@lintworm , Samburu NR, Kenya


@lintworm , Samburu NR, Kenya

Bushpig

The Bushpig (Potamochoerus larvatus) is a species of pig with a wide distribution in Eastern and Southern Africa. It has also been introduced to Madagascar. Up to six subspecies have been described, but their validity is unknown. Kingdon recognized 3 subspecies.

P.l. hassama E Africa
P.l. koiropotamus S Africa
P.l. somaliensis Somalia

The nominate has been described from Madagascar.

Potamochoerus larvatus koiropotamus

@gentle lemur , Artis, Amsterdam, Netherlands

Bushpig from Madagascar:

@lintworm , Tzimbazaza Zoo, Antananarivo, Madagascar

Red river hog

The Red river hog (Potamochoerus porcus) is a monotypic pig species that occurs in W and C Africa.


@geomorph , Sedgwick County Zoo, USA


@KevinB , Gaiazoo, Kerkrade, Netherlands

References

Muwanika et al. (2003): Phylogeography and population structure of the common warthog (Phacochoerus africanus) inferred from variation in mitochondrial DNA sequences and microsatellite loci

 

According to IUCN red list they might constitute a separate subspecies, but the article on that was still in preparation at the time of the red list assessment.

 

Vicuna

The Vicuna (Vicugna vicugna) is a small species of camelid from the Andes, ranging from Peru through Bolivia to northern Chile and Argentina. Traditionally two subspecies are recognized:

V.v. vicugna S Bolivia, NW Argentina, N Chile
V.v. mensalis Peru, extreme NE Chile, W Bolivia

G&G elevate mensalis to species status.


Sample size

No sample size for skins is given

Skulls
vicugna 2-3
mensalis 9-14

Sample sizes are thus extremely low for vicugna.


Skins

Mensalis has a long mane on the chest and lower throat and colour is described as dark cinnamon with white on the underside. White markings are more extensive in vicugna, which also has a light beige pelage.


Skulls

Skulls of vicugna are described as much larger, which is true on average, but with most measurements there is clear overlap with mensalis. Teath of vicugna are longer than mensalis, but sample size here is very limited. Despite on average larger size, vicugna is said to have lower nasal and diastema length, but data are not presented.


Additional data

G&G cite a study by Marin et al. (2007) which shows that there is some genetic differentiation between vicugna and mensalis in mitochondrial dna. A recent, more extensive study by Gonzalez et al. (2019) does find minor differences in mtdna, between the taxa, but the microsatellite markers show that genetic differentiation is best explained as an isolation by distance pattern. In such a pattern the populations furthest apart are most different and intermediate populations have more intermediate characteristics.


Summarizing

Given new dna evidence there seems no basis to accept the proposed split. Additionally the described skull differences are rather minor. It also does not seem that more research would change that picture, so there really is only one species of Vicuna


Vicugna vicugna mensalis

@Giant Eland, Parque Zoologica Huachipa, Lima, Peru

Zoo Vicuna:

@KevinB , Dierenpark Planckendael, Mechelen, Belgium

References

Gonzalez et al. (2019): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6562099/

Marin et al. (2007): Mitochondrial phylogeography and demographic history of the Vicuña: implications for conservation

 

Guanaco

The Guanaco (Lama guanicoe) is a camelid native to South America and is widely distributed in Argentina, S and NE Chile, S Bolivia and Peru. Up to four subspecies have been recognized, but based on morphological and genetic data only two should be recognized:

L.g. guanicoe Chile, Argentina, Bolivia
L.g. cacsilensis Peru

Lama guanicaoe guanicoe

@lintworm , Pali Aike NP, Chile

Zoo Guanaco

@Arek , Zoo Wroclaw, Poland

Wild Camel

The Wild camel (Camelus ferus) is a critically endangered camelid with a relict distribution in N China and S Mongolia. This species has long been thought to be the ancestor to the domestic camel, but genetic research has indicated that this is not true and the Bactrian camel is a separate species, whose wild ancestors are now extinct (Ji et al., 2009)


@baboon , Great Gobi A SPA, Mongolia


Then there are two domestic species, whose wild ancestors are now extinct:

Dromedary camel

@Patrick87 , Zoo Berlin, Germany

Bactrian camel

@KevinB , ZooParc Overloon, Netherlands

References

Ji et al. (2009: Error - Cookies Turned Off)


And with that the Even-toed ungulates are complete.

 

And how does G&G classify the Domestic Pig?

 

It is a domestic species so none of their concern...

 

Mountain zebra

The Mountain zebra (Equus zebra) is a species of Zebra with a restricted distribution in Namibia and South Africa. Two subspecies are currently recognized:

E.z. zebra Cape mountain zebra, Cape regions, South Africa
E.z. hartmannae Hartmann’s mountain zebra, W Namibia to the South-African border

G&G recognize both subspecies as a monotypic species.


Sample size

G&G base their conclusions on a study by Groves & Bell (2004). No sample sizes are stated in this study for Mountain zebra. Based on their figures, samples are less than 10 for each taxon.


Skins

In zebra the black stripes are much wider in relation to the white interspaces compared to hartmannae.


Skulls

On multivariate analyses zebra and hartmannae group pretty much apart, this is mainly because hartmannae is on average larger and there is no difference in size between the sexes. In zebra males are significantly smaller than the females. Female hartmannae are on average larger than female zebra, but I am not sure whether this difference is significant, especially when more samples would be considered. Zebra is also said to have a broader muzzle and longer diastema


Additional data

A paper by Moodley & Harley (2005) analysed genetic differences between Mountain zebra populations based on mitochondrial dna. They did not find that both taxa were reciprocally monophyletic, but mixed. They did however find that both taxa have several private alleles, not shared with the other. They estimated a time of divergence of 362.000 years between both taxa. I am however not sure how reliable that number is as both taxa have gone through a bottleneck, which can lead to an overestimation of divergence times.


Summarizing

From a strict PSC perspective this would be a clear case of two separate species, but that would be oversimplifying the current findings. It would be interesting to do additional research on nuclear dna and try to understand more clearly the genetic relationships between both taxa, as with current data a split would mean 2 paraphyletic species. For now it seems most appropriate to retain one species of Mountain zebra, with two well-defined subspecies.

Equus zebra zebra

@Bele , Bontebok NP, South Africa

Equus zebra hartmannae

@Tim May , Marwell Wildlife, UK


References

Groves & Bell (2004): https://sci-hub.tw/https://www.sciencedirect.com/science/article/abs/pii/S1616504704701160

Moodley & Harley (2005): Population structuring in mountain zebras ( Equus zebra ): The molecular consequences of divergent demographic histories

 

It's nice to see the thread moving along well. Keep up the incredible work!

 

Asiatic wild asses

Generally two species of Asian wild asses are recognized: the Kiang (Equus kiang) from the highlands of Tibet, Ladakh & Sikkim (India) and Sichuan and the Asian wild ass (Equus hemionus) from Mongolia, the Stans, Iran, W India and formerly the parts of the Middle East. For each species multiple subspecies are generally recognized:

Equus kiang
E.k. kiang Ladakh, India, and Tibet
E.k. holdereri E Tibet & W plateau of Sichuan, China
E.k. polyodon Sikkom Plateau, India

Equus hemionus
E.h. hemionus Dziggetai/ Mongolian wild ass, Mongolia, and neighbouring parts of Siberia and W into Xinjang, China (includes luteus)
E.h. kulan Kulan, Turkmenistan
E.h. onager Onager, Iranian plateau, introduced in Israel
E.h. khur, Khur/Indian wild ass, Little Rann of Kutch, India
E.h. hemippus Syrian wild ass/Achdari, extinct, formerly Iraq, Jordan and Palestina.

Current distributions are remnants of its (pre-)historical distribution

G&G elevate both hemippus and khur to species status, leaving the rest of the previous arrangement in place.


Sample size

No sample sizes for skins are given.

Skulls (males/females)
hemionus 0/2
luteus 12-13/10
kulan 2-5/6-10
onager 4/2
khur 3/2
hemippus 1/2-3

All data come from Groves & Mazak (1967). Most sample sizes are very small


Skins

hemippus is described as having an intergrading desert coloration, general color of khur is not given, but the white of the belly reaches at least halfway up the flanks. khur has no hoof rings, whereas these were present in hemippus and the other taxa. In hemippus dorsal stripe extends to the tail-tuft, in khur this ends at the or slightly beyond the base of the tail, this dorsal stripe is vague/absent in the other taxa


Skulls

khur is described as being somewhat smaller in size compared to hemionus, kulan and onager and hemippus is even smaller. Overlap in the measurements between taxa is somewhat limited, but sample sizes are very small. Additionally some other skull differences are described. Skull of khur and hemippus is described as very high crowned and high crowned respectively, and low-crowned for the other taxa. dorsal outline of the skull of hemippus is given as concave and sinuous for khur, but is given as very straight for the other taxa.


Additional data

Genetic research, looking at mitochondrial dna, gives a completely different picture then the 4 species proposed by G&G. Bennett et al. (2017) (which is a manuscript that I recommend you to read) find that both khur and hemippus are firmly nested within Equus hemionus, with hemippus sister to Onager and khur sister to Kulan & part of the Dziggetai population. More surprisingly is that they find that Kiang clusters together with a large part of the Dziggetai population. This would leave Dziggetai (the nominate hemionus) paraphyletic, based on current knowledge and would mean that Kiang is not actually a distinct species but more likely a subspecies / population that has successfully adapted to a different environment (high elevation plateaus as opposed to (lowland) steppe/desert). Bennett et al. (2017) hypothesize that the small size of hemippus is an evolutionary very recent event. Additionally Kaczensky et al. (2018), who studies kulan and onager find no evidence for two different subspecies, but rather a cline from N to S. Previously there will have been gene flow between these now separated populations.

Older studies did not find that Kiang is nested within hemionus (e.g. Oakenfull et al., 2000), but they did have any Dziggetai samples, so that result is not surprising. That Kiang might not be a separate species was already noted in 2005 by Krueger et al.

Chromosomal variation is high in Asiatic wild asses, with chromosome counts of 2n=54,55 and 56 reported for kulan and onager and 2n= 52 or 51 for kiang (Ryder & Chemnik, 1990). There thus seems to be large variation, but whereas onager and kulan show overlap with each other, there is none with kiang. It would however be interesting to see what the chromosome count is of the Dziggetai.


Summarizing

Asiatic wild asses are a evolutionary very interesting example in which one widespread species has adapted to a large number of ecotypes in extremely different environments across Asia. Current distributions are misleading, as they are mostly just remnants. Whereas originally two species were recognized, based on current genetic evidence, they are best lumped, even though morphological differences can be quite large. There is also no genetic evidence for splitting khur or hemippus. It would be interesting to study in detail the chromosome number of the Dziggetai and compare it with Kiang and see whether nuclear dna gives a different picture than mtdna.

Even though 8 subspecies have generally been recognized, it is even questionable as to whether they can be referred to as subspecies, or mere ecomorphotypes. The last word on Asiatic wild ass taxonomy has certainly not been said, but for now it seems best to lump Kiang back into the Asian wild ass and I will provisionally remain recognizing the subspecies until a clearer picture has emerged as to how to treat them, except for Onager and Kulan.

Equus hemionus hemionus s.l.

@Deer Forest , Tianjin Zoo, China

Equus hemionus kiang

@Patrick87 , Tierpark Berlin, Germany

Equus hemionus onager

"Onager"

@demonmoth , Chester Zoo, UK

"Kulan"

@Tim May , Tiergarten Nürnberg, Germany

Equus hemionus khur

@Chlidonias , Little Ran of Kutch, India


References

Bennett et al. (2017): Taming the late Quaternary phylogeography of the Eurasiatic wild ass through ancient and modern DNA

Groves & Mazak (1967): Bd.32 (1967) - Zeitschrift für Säugetierkunde : - Biodiversity Heritage Library

Kaczensky et al. (2018): Genetic characterization of free-ranging Asiatic wild ass in Central Asia as a basis for future conservation strategies

Krueger et al. (2005): Error - Cookies Turned Off

Oakenfull et al. (2000): A survey of equid mitochondrial DNA: Implications for the evolution, genetic diversity and conservation of Equus

Ryder & Chemnick (1990): Chromosomal and molecular evolution in Asiatic wild asses

 

Grevy's zebra

The Grevy's zebra (Equus grevyi) is the largest Zebra species. This monotypic species is currently restricted to N Kenya and a remnant population on the Aledeghi plains in Ethiopia. Formerly this species occured throughout the horn of Africa.


@Tim May , ZSL Whipsnade Zoo, UK

Plains zebra

The Plains zebra (Equus quagga) is a widespread equid from savannahs in Southern and Eastern Africa. Six subspecies are generally recognized:

E.q. quagga Quagga, Cape province, South Africa, now extinct
E.q. burchellii Burchell's zebra, Namibia, S Botswana, Swaziland, parts of South Africa (includes antiquoroum)
E.q. chapmani Chapman's zebra, NE South Africa, Zimbabwe, N & E Botswana, Caprivi Strip (Namibia), S Angola
E.q. boehmi Grant's zebra, Zambia, W of Luangwa River, Tanzania, SE DR Congo, Kenya, Rwanda, SW Uganda, S, W & E Kenya, S Ethiopis
E.q. borensis Half-maned zebra, NW Kenya, Karamoja District (Uganda) and SE South Sudan
E.q. crawshaii Zambia, E of Luangwa River, SE Tanzania and parts of Mozambique

Genetic research does however show a different picture than the subspecies above, which are based purely on morphological criteria. Pedersen et al. (2019) show that genetically there are 9 distinct populations, which could be regarded as subspecies. crawshaii, quagga, burchelli, chapmani and borensis are all retained. But boehmi in fact comprises 4 somewhat distinct populations: 1) Kenya and N Tanzania ("Grant's zebra") 2) SW Uganda & Rwanda ("Ugandan plains zebra) 3) SW Tanzania ("Rukwa plains zebra") 4) Zambia ("Zambian plains zebra).

There is no evidence that these all represent distinct species, so a more appropriate view would be to recognize 9 subspecies, some of which cannot (yet?) be identified on morphological characteristics.

Equus quagga quagga

@twilighter , Musee national d'histoire naturelle, Paris, France

Equus quagga burchellii

@Kudu21 , Amakhala PGR, South Africa

Equus quagga chapmani

@Kudu21 , Kruger NP, South Africa

Equus quagga boehmi s.l.

Ugandan plains zebra

@Hix , Lake Mburo NP, Uganda

Grant's zebra

@Hix , Tarangire NP, Tanzania

Equus quagga borensis

@ro6ca66 , Colchester Zoo, UK

African wild ass

The African wild ass (Equus africanus) is a critically endangered Equid from NE Africa. Two subspecies are generally recognized, one of which is possibly extinct. There has been some debate as to whether both subspecies should be recognized as species in their own right.

E.a. africanus Nubian wild ass, NE Sudan into northernmost Eritrea, possibly extinct
E.a. somaliensis Somali wild ass, C and S Eritrea, NE Ethiopia.

Equus africanus africanus

uploaded by @vogelcommando , Zoo Berlin, Germany

Equus africanus somaliensis

@Tim May , Tiergarten Nürnberg, Germany

Przewalski's horse

The Przewalski's hore (Equus ferus przewalskii) is currently lumped with the Tarpan (Equus ferus ferus), but both populations diverged about 250.000 years ago and have a different chromosome count. Despite this hybrids do produce fertile offspring. There is however a case that they could be split again.

Equus ferus przewalskii

@Arek , Zoo Liberec, Czech Republic


References

Pedersen et al. (2019): http://www.the-eis.com/data/literat...e highly mobile plains zebra_Online Early.pdf

 

Lowland tapir

Lowland tapir (Tapirus terrestris) has traditionally been treated as a monotypic species. In 2013 Cozzuol et al. (2013) described a new species of Tapir: Tapirus kabomani. The description was based on analysis of skulls, pictures, local knowledge and genetics. Tapirus kabomani is reportedly a species with a widely overlapping distribution with the Lowland tapir and is genetically the sister group to Lowland + Mountain tapir. This view has since been questioned by multiple studies, most notably Voss et al. (2013) and Ruiz-Garcia et al. (2015). Their research shows that genetic differences between the reported kabomani samples and other Lowland tapir are low (~1,5%) and their follow-up analyses with genetic data do merge kabomani with other Lowland tapir. The position of Mountain tapir is not completely clarified, but in analyses by Ruiz-Garcia et al. (2015; 2016), who used the largest dataset of all studies, this species is monophyletic and sister to kabomani + Lowland tapir. The find three main haplogroups within Lowland tapir, one of which consists of the kabomani specimens. Additionally new morphological research does not clearly separate kabomani from Lowland tapir (Dumba et al. 2019). More data is necessary to find out how this kabomani samples relate to sympatric Lowland tapir. But treating them as a separate species is not warranted.


@vogelcommando , Artis Royal Zoo, Amsterdam, Netherlands

"kabomani tapir"

@alexkant , Parque Jaime Duque, Colombia

Mountain tapir

The Mountain tapir (Tapirus pinchaque) is a monotypic species of Tapir endemic to the Andes of Ecuador, Colombia & N Peru.


@alexkant , Zoologico de Cali, Colombia


Baird's tapir

Baird's tapir (Tapirus bairdii) is a monotypic Tapir species that occurs in Central America from N Colombia to C Mexico.


@Maguari , Zoo Wuppertal, Germany


Malayan tapir

The Malayan or Malay tapir (Tapirus indicus) is a monotypic species that occurs in SW Thailand, Peninsular Malaysia and Sumatra. Based on it long evolutionary divergence and unique morphology, this species might be better placed in the monotypic genus Acrocodia


@Jogy , Wilhelma, Stuttgart, Germany

References

Cozzuol et al. (2013): https://www.researchgate.net/profil...00/A-new-species-of-tapir-from-the-Amazon.pdf

Dumba et al. (2019): Cranial Geometric Morphometric Analysis of the Genus Tapirus (Mammalia, Perissodactyla)

Ruiz-Garcia et al. (2015): https://www.researchgate.net/profil...th_America/links/555f879b08ae8c0cab30b391.pdf

Ruiz-Garcia et al. (2016): https://www.sciencedirect.com/science/article/abs/pii/S1616504715001068#!


Voss et al. (2014): Extraordinary claims require extraordinary evidence: a comment on Cozzuol et al. (2013)

 

Greater one-horned rhinoceros

The Greater one-horned rhinoceros or Indian rhinoceros (Rhinoceros unicornis) is a monotypic species which currently occurs in N India and S Nepal.


@gentle lemur , ZSL Whipsnade Zook, UK


Javan rhinoceros

The Javan rhinoceros or Lesser one-horned rhinoceros (Rhinoceros sondaicus) is a critically endangered species, whose current distribution is limited to Ujong Kulon NP on the western tip of Java, Indonesia. This species was formerly widespread across SE Asia, but both mainland subspecies annamiticus and inermis are now extinct. The nominate sondaicus formerly occurdes on Java, Sumatra and Peninsular Malaysia, but is now restricted to a single location.


uploaded by @Joker1706 , ZSL London Zoo, UK


Sumatran rhinoceros

The Sumatran rhinoceros (Dicerorhinus sumatrensis) is a critically endangered species, whose current wild distribution is restricted to Sumatra and maybe Borneo. Originally three subspecies have been recognized, of which the most northern one lasiotis is already extinct. Steiner et al. (2017) have confirmed the validity of the three subspecies using genetic data and they estimate a divergence time of 80.000 years ago.

Dicerorhinus sumatrensis sumatrensis

@Lemurs , Port Lympne Wild Animal Park, UK

Dicerorhinus sumatrensis harrisoni

@easytigger, Lok Kawi Wildlife Park, Malaysia


Black rhinoceros

The Black rhinoceros (Diceros bicornis) is a critically endangered species that formerly occured throughout E and S Africa and even west to E Nigeria. The current distribution is very patchy in S and E Africa. Up to 8 subspecies have been described, of which chobiensis is of very limited validity. The subspecies bicornis, brucii, ladoensis, longipes are now extinct, leaving only three extant subspecies: minor of SE Africa (north into Selous ecosystem, Tanzania), occidentalis of N Namibia, and michaeli of N Tanzania and Kenya. The population in Namibia is often wrongly referred to as bicornis, but is occidentalis according to G&G.

Diceros bicornis michaeli

@MagpieGoose , Folly Farm, Begelly, UK

Diceros bicornis minor

@snowleopard, Zoo Frankfurt, Germany

No pictures of occidentalis have been uploaded to the gallery yet.


Reference

Steiner et al. (2017): Genetic variation of complete mitochondrial genome sequences of the Sumatran rhinoceros ( Dicerorhinus sumatrensis)

 

What is the third Sumatran rhino subspecies called?

 

White rhinoceros

The White rhinoceros (Ceratotherium simum) is the largest extant Rhinoceros species and also the most common. Generally two subspecies are recognized:

C.s. simum Southern white rhinoceros, Africa S of the Zambezi, introduced outside original native range in Kenya, Uganda
C.s. cottoni Northern white rhinoceros, E and C Africa, currently down to two individuals kept in captivity in the Ol Pejeta Conservancy, Kenya.

G&G elevate cottoni to species status, which would make this taxon the rarest species worldwide.


Sample sizes

The split is based on a publication by Groves et al. (2010).

Skulls (males/females)
simum 8/5
cottoni 18/14

Body measurements
simum 10-11/4-8
cottoni 2-3/6

Sample sizes are relatively low.


Skins/Body measurements

On average cottoni is smaller than simum, but there is overlap between the measurements, both when looking at body length and height. simum has a more wrinkled body than cottoni. In general cottoni animals often have more hairy ears and tails, but less hairy bodies. With these characteristics there seems to be quite some variation within each taxon as well. Northern rhino are reported to be much lighter, especially in the case of males (Hilman-Smith et al., 1986). Some of the body measurements come from animals in captivity and might thus not be completely reliable.


Skulls

A number of small differences in the skulls are described in Groves et al. (2010), largely based on limited evidence. In most measurements it is clear that on average cottoni is smaller than simum. There are clearer differences described in dental morphology. Several figures are missing from the manuscript (but present in the description) and one should have shown dorsal concavity relative to occipitonasal length, which should have given a clear difference (Figure 6c in manuscript). In the field cottoni has a noticeably shorter skull than simum.


Additional data

Groves et al. (2010) state that the time of divergence between simum and cottoni is 1.84 million years ago, based on a very limited sample. This is an overestimate. A whole mitochondrial genome analysis by Harley et al. (2016) put the date of divergence at somewhere between 0.46 and 0.97 mya. A study by Sanchez-Garcia & Castresana has shown that mitochondrial divergence can predate the actual lineage divergence by as much as 300%. It is thus possible that the actual divergence only took place 200.000 years ago. This is thus also an issue with most of the divergence times mentioned earlier in this thread. In addition to the initial divergence there is clear evidence of simum and cottoni interbreeding during glacial maximums, including possibly the last glacial maximum (Moodley et al. 2018). In addition Moodley et al. (2018) find evidence of range expansions and contractions based on climatic fluctuations. There have been times where White rhino populations were continuous throughout Africa and the disjunct historic distribution does not tell the whole story.

Cinkova & Policht (2014) found small but noticeable differences between the calls of simum and cottoni. Groves et al. (2010) state that a cottoni X simum hybrid had potentially reproductive problems, a case that would strongly suggest they should be classified as separate species. There is however only very scant anecdotal evidence for this and observations from Ol Pejeta show that mate recognition at least is not the problem. Recent interbreeding as shown by Moodley et al. (2018) would also point against this being the case


Summarizing

The White rhinoceros is a clear example to show that taxonomy very much matters. It shows that the species is the unit in biology that matters most. It is at the species level that conservation actions are mostly decided.Classifying cottoni as a separate species would have very clear conservation implications and the potentially necessary step of interbreeding cottoni with simum to partly save cottoni would be a step too far.

I am personally not convinced that cottoni should be split, the morphological differences are there, but rather small and the genetic data show a much more complicated picture. This is also the main problem I (and many professional taxonomists) have with the Phylogenetic Species Concept. It offers a "convenient and tidy" solution to the species problem: diagnosability. If a population is different in even just one character it is different. G&G even explicitly state that "that fixed differences should not be evaluated in the context of their biological significance or the underlying divergence process" (Harley et al. 2016). In such a world every tiny difference that can be found, is evidence for a new species and as the Klipspringer example (and many others by G&G) has shown this leads to tremendous oversplitting based on tiny sample sizes and faulty use of statistics. If adapted it could have disastrous consequences for conservation. It would be nice to have such a simple solution to the species problem, but even if it is used correctly, it completely ignores evolutionary complexity and phenotypic plasticity and an elegant solution becomes an oversimplified solution. There is currently a minor, but very vocal, group of scientists defending the findings by G&G, but none of them has actually touched upon the quality of the evidence that has been provided by G&G and several of them make dubious claims about splitting, as yet untouched, species such as Bongo. The whole scientific discussion in recent years has mostly focused on who has the "right" species concept. I personally do not believe that there is one "right" species concept and I think you need to incorporate multiple lines of evidence to decide whether to split a species. I hope that this thread has given you a better insight in what is going on in ungulate taxonomy. I also sincerely hope that scientists will soon stop bickering about species concepts and identify a way forward and find common ground on where the old taxonomy is indeed outdated (such as in Bushbuck & Brocket deer) or more research is needed (such as in Mountain reedbuck & Blue duiker). A good paper by Gutierrez & Garbino (2018) on this is linked below. With the White rhinoceros we come to the final ungulate species. I will create a final post which would propose such a way forward, based on actual evidence. For now thank you for being patient for 3.5 years to follow this thread.


Ceratotherium simum simum

@Himimomi , Nanning Zoo, China


@Jogy , Lake Nakuru NP, Kenya


Ceratotherium simum cottoni

@lintworm , Ol Pejeta Conservancy, Kenya


@lintworm , Ol Pejeta Conservancy, Kenya


References

Cinkova & Policht (2014): Contact Calls of the Northern and Southern White Rhinoceros Allow for Individual and Species Identification

Groves et al. (2010): The Sixth Rhino: A Taxonomic Re-Assessment of the Critically Endangered Northern White Rhinoceros

Gutierrez & Garbino (2016): Species delimitation based on diagnosis and monophyly, and its importance for advancing mammalian taxonomy

Harley et al. (2016): Comparison of whole mitochondrial genome sequences of northern and southern white rhinoceroses ( Ceratotherium simum): the conservation consequences of species definitions

Moodley et al. (2018): https://royalsocietypublishing.org/...x5AL-hTAP1yvPG3DIRK4JcxjqWkGXOgpnyzpGKGKj98Qg