Equus hydruntinus, the enigmatic European wild ass

After finally having done a post on Bubalus murrensis, it’s time to look at the extinct European wild ass, Equus hydruntinus. This enigmatic taxon once roamed Europe during the Pleistocene until the a part of the Holocene, and its presence is therefore interesting for “European rewilding”. This post is going to investigate its systematic position, time and range, looks and reasons for extinction. And of course which implications it has for the (re)introduction of megafauna here in Europe.

But before that, there is some (paleo-)equine terminology to learn:

caballines: anything closer to horses than to other living equines (or: domestic horses opposed to the Przewalski’s horse)

hemiones: E. hemionus plus E. kiang, which form a clade

stenonines:  Equus stenonis plus similar equine remains from the Plio-Pleistocene.

asinines: anything closer to the African wild ass E. asinus than to other living equines.

Skull of E. hydruntinus from Crimea, taken from [4]

Equus hydruntinus was a small equine with a gracile and cursorial build. It has been difficult to classify it for a long time. The remains were only sparse and mostly fragmentary, and it seemed that it showed a mosaic of characters [1;2]. The elements used for a phylogenetic classification based on skeletal morphology were mostly limb elements, tooth and – after two almost complete crania were found [3,4] – also skull proportions. Because of this morphological mosaic of characters, it has been variously classified as a donkey relative, a zebra relative, hemione and stenonine [1] since it shares characters with most Equus clades with the exception of horses.

The similarity to stenonine horses was based tooth characteristics [1], while its leg bones and skull morphology was reminiscent of hemiones and asinines [1]. A dental similarity with hemiones has also been pointed out, but also that there seems to be a certain degree of polymorphism within equines [5], making this feature less useful for evaluating systematic positions.

Nevertheless, there is a general agreement that morphological characters suggest that Equus hydruntinus was a distinct species, differing from but also resembling its Equus relatives in a number of features [5]. What is important to note is that hydruntinus was sympatric with other of species/subspecies in a number of regions, such as caballines, asinines, E. h. hemionus and E. h. hemippus [5]. It is out of question that hydruntinus was a horse due to the lack of morphological similarity. Its coexistence with sp. hemionus subspecies sheds doubts on the hypothesis that hydruntinus was a member of this species because they would interbreed and merge together, even if they occupy different ecologic niches. You will find no example of two subspecies of a species inhabiting one and the same biotope. The idea that hydruntinus occupied a different ecological niche is supported by its small size and different tooth morphology. Even within the clade of hemionus + kiang, hydruntinus seems to be kind of a patchwork of characters: the metapodials are as long as in the Kulan, the teeth and protocones are as small as in the Syrian wild ass.

However, since osteomorphologic characters alone are not ideal to create a solid hypothesis on hydruntinus’ identity due to intraspecific variation and the scarcity of the fossil/subfossil material. Therefore, genetic studies are needed to help to clarify.

Orlando et al. 2006 and 2009 did such studies using aDNA of the mitochondria. They found Equus hydruntinus showing no affinity to the Burchell’s zebra and asses (2006)[3] to be nested within Equus hemionus (2009)[2]. Together they share a 28-bp deletion in the mitochondrial HVR-1 gene [2]. They conclude that the hydruntinus therefore is a subspecies of Equus hemionus. On the other hand, kulan/onager and kiang are regarded as separate species because of different coat colour, morphology and karyotype yet show poor mitochondrial differentiation [2] (the coat colour and karyotype of hydruntinus are not even accessible to us). Another issue is that also the Grevy zebra is nested within the hemionus group (yet not showing the 28-bp deletion). Therefore Orlando et al. suggest that nuclear loci are needed to further clarify the relationships of E. hydruntinus.

Possible depiction of E. hydruntinus from the Chauvet cave (Bottom)

What we know from skeletal remains, including relatively recent finds of a nearly complete skeleton from Iran and two well-preserved crania from Crimea [3], E. hydruntinus was a small equine (smaller even than hemionus and hemippus) with gracile and cursorial legs. The body was short and the backline, typically for wild asses, straight or slightly convex. The muzzle was comparably short in the well-preserved crania – this has been interpreted as an adaption to cold climate [3], but I consider that premature because this based on pretty scanty data and equines have much cranial variation [3]. As an ass, it very likely had long ears, a short mane and its tail only had a short tassel on its end. But apart from that, we do not know much about its outer appearance because it is not nearly as often represented in coloured paintings as aurochs and wild horses are. There is one coloured painting in Lascaux that may or not may be a wild ass, the equine next to it is undefinable. Assuming it is E. hydruntinus, it might implicate it was of a dark brown colour. But this is nothing but a weak hint, the European wild ass might have had any colour nuance displayed by modern equines with a bay dun colour. There is another possible depiction of E. hydruntinus at Chauvet that shows a panel of wild horses plus an equine at the bottom which might be an ass because of the different, ass-like head shape and possibly long ears. In this case we might infer that E. hydruntinus was of a darker colour with a clearly recognizalbe muzzle ring. Or maybe it was another species of ass. Or maybe not an ass at all. The data is simply not sufficient.

Obviously E. hydruntinus is morphologically and genetically distinct enough to distinguish it from other members of the genus and to reconstruct a geographic and geologic range. The species seemingly had been existing since the Middle Pleistocene. In Europe, the  main body of its geographic range was Southern Europe, which also was a refuge for this and many other species during the last glacial maximum [3]. Its northwards range during the Pleistocene was restricted only by the ice sheaths. It went up was much north as UK or Germany [3] in the past. Findings in Siberia that have been previously assigned to hydruntinus in fact turned out to be related to Equus sussenbornensis, a more basal species from Germany, with which it forms the now extinct group of the sussemiones. Eastwards, its range reached as far as Iran[3], where it coexisted with E. h. hemionius but also Syria [3], where its range overlapped with the Syrian wild ass E. h. hemippus.  

The European wild ass died out comparably recently. It occurred in the subfossil record until the Iron Ages. For example, there is a solid record of the species in Neusiedl in the east of Austria (Pucher 1991 [6], Erich Pucher in personal communication 2012). The hypothesis that Equus hydruntinus is the mysterious “zebro” of the Iberian peninsular in historic time has always been controversial. For once, the “zebro” was described as an equine clear striping, while hemiones – which are most likely the closest relative of hydruntinus – do not show striped patterns, only a very faint shoulder streak in some cases. The skeleton of the alleged last zebro from the 17^th century turned out to be a donkey [2]. So there are no remains that suggest it survived beyond the Iron age.

The sites where it was found suggest it was an animal of dry and open areas, like other asses. In fact even the location in Austria where it was found, Neusiedl, is sometimes described as a “small exclave of the Puszta”.

The fact that Equus hydruntinus was not as prevalent in prehistoric art as other mammals were might implicate that it was not that spectacular and important to humans and not all too numerous. The last point is indeed supported by fossil and subfossil evidence to a certain degree. By the Holocene, its range was apparently highly fragmented [3] Probably this was originally the result of ecologic changes at the end of the last glacial [7], but it was probably human hunting and habitat loss that made it a true extinction process. Although it seems that it was not one of the most important game species for humans, there is evidence from several sites that this species was seized by man [7]. Particularly the fact that the population seemingly began to drop from the Neolithic onwards is indicative of human influence [7]. Therefore it is likely that the European wild ass would have recovered from the ecological changes that occurred by the end of the last glacial if there had not been anthropogenic factors, similar to the case of giant deer [7] or the woolly mammoth. So it might still inhabit at least some regions of Europe, particularly the dry and open ones. I cannot speak for the Near and Middle East.

So my view on wild asses in Europe is similar to that on water buffalo. I think it is O.K. to use a closely related and ecologically probably similar species to replace hydruntinus in some regions, be it kulan or onager (I favour kulan). But European reserves probably would do well without them as well. Whether it would be an ecologic benefit I cannot say, but it probably would do no harm either. But a claim that it is a “necessary keystone species” would be, in my opinion, baseless. Regions that might be best-suited for wild asses might be the Balkan, Eastern European steppe-like environments such as the Hungarian Puszta, and probably also the Italian and Iberian peninsular.

Literature

1. A. Burke, V. Eisenmann, G.K. Ambler: The systematic position of Equus hydruntinus, an extinct species of Pleistocene equid. 2003.

2. L. Orlando et al.: Revising the recent evolutionary history of Equids using ancient DNA. 2009.

3. L. Orlando et al.: Geographic distribution of an extinct equid (Equus hydruntinus: Mammalia, Equidae) revealed by morphological and genetical analyses of fossils. 2006.

4. E.N. van Asperen, K. Stefaniak, I. Proskurnyak, B. Ridush: Equids from the Emine-Bair-Khosar Cave (Crimea, Ukraine): co-occurrence of the stenoid Equus hydruntinus and the caballoid E. ferus latipes on skull and postcranial remains. 2012.

5. E.-M. Geigl, T. Grange: Eurasian wild asses in time and space: Morphological versus genetical diversity. 2012.

6. E. Pucher: Erstnachweis des Europäischen Wildesels (Equus hydruntinus, Regalia, 1907) im Holozän Österreichs. 1991.

7. J.J. Crees, S.T. Turvey: Holocene extinction dynamic of Equus hydruntinus, a late-surviving European megafaunal mammal. 2014.

The European water buffalo / water buffalo in Europe

During the Pleistocene and probably also until the antiquary, Europe was not inhabited by only two species of bovine – aurochs and wisent – but three. This third bovine was Bubalus murrensis, an indigenous species of water buffalo. It is extinct and left no living descendants. Nowadays, due to the European rewilding movement, the genus Bubalus has gained some interest for landscape conservationists and “rewilders”. It is important to distinguish between living European variants of the domestic water buffalo, descending from the Asiatic Bubalus arnee, and the indigenous species B. murrensis.

Are water buffalos a perspective for conservation in Europe, and are they further a legitimate megafauna species on this continent?

Bubalus murrensis – the true European water buffalo

B. murrensis was part of a clade within Bubalus that is now extinct and that was different from B. arnee. Since the postcranial skeleton of large bovines are all very similar, most material assigned to that species are skulls.  

It was part of the interglacial fauna, like the aurochs and unlike steppe bison and mammoth. It seemingly disappeared at the end of the Pleistocene or early Holocene. There is sparse Neolithic postcranial material from the East of Austria that have been tentatively assigned to Bubalus by Pucher 1991 [1]. About three years ago, I had email conversation with Erich Pucher about his findings, and he told me that the assignment to Bubalus was on weak ground and he would reclassify them as Bos nowadays. I do not know of more Holocene material that might or might not be remains of B. murrensis, although there is the chance that a number of postcranial elements were erroneously assigned to Bos or Bison. 

B. murrensis cranium at the left; others are Russian Bubalus sp. specimen.

I composed a picture showing a number of buffalo specimen that are extinct species of Bubalus. The only one I know for sure to be murrensis from Germany is the one at the top left, provided by Markus Bühler. The other ones are buffalo skeletons that I found on Russian websites, perhaps they are Asiatic relatives that might provide some clue how their European pendant looked like. The European water buffalo had horns that resembled those of the smaller tamaraw (B. mindorensis) more than the Asiatic water buffalo in that they were oriented more backwards and were not as strongly curved, and their horns probably lacked an upwards curve. Other than that, the rest of the animal might have been quite alike its relatives as bovines do not vary that much in that respect… At the right at the top there is a beautiful life restoration of B. murrensis.

It lived near freshwater habitats just like other members of this genus, many of the remains assigned to this species are from the Netherlands and Germany. A lot of evidence for its presence was found in the Rhone valley, which also was home to the hippopotamus during the Eem interglacial. Bioindicator species suggest that this region was a mosaic of open grassland and forested areas [2]. Due to the sparse palaeontological information we do not know much about its ecology and behaviour. I think it is sound to assume that it was ecologically very similar to its two living relatives, feeding on grasses and water- and swamp plants on watersides of their wetland habitats. We have no clue how gregarious they were. Tamaraw are mostly solitary, while Asiatic water buffalos roam in groups of up to 30 individuals, similar to aurochs/cattle. Probably they were more similar to the latter. I wonder how common they were. There seem to be only very few artistic references to this species in prehistoric art – I only know of petroglyphs from the French cave of Bourdeilles dating back 18.000 years ago that are often believed to show aurochs but I think they more likely depict buffalo because of the horn and head shape. The rarity of artistic references might implicate that B. murrensis was not an important animal in the world of the paleolithic people, perhaps it was a comparably rare animal. But this is speculation. Since it seemingly was not illustrated on coloured cave paintings, we have no idea of its coat colour. Since tamaraw, some domestic and wild Asiatic buffalo have the same “markings” in the form of white areas on their upper lips (something like a very reduced version of the “mealy mouth” in cattle), sometimes also a white tail tip and a crescent-like streak on the ventral side of their neck (I don’t know if there is a particular name for it, call it “neckband”), these markings might have been present in the European water buffalo as well. The rest of the coat colour might have been solid, like in all the other buffalos. Of course we have no idea of the shade of its colour – it might have ranged from greyish over light brown to dark brown or black. Or perhaps it even was a totally different colour… My amateurish illustration on deviantArt shows one possibility.

Domestic buffalo in Europe

Bubalus arnee, the wild Asiatic buffalo, was domesticated about 5000 years ago (the exact time of domestication is a matter of discussion), probably in two separate events by the Indus culture and China [3]. From the Middle East, the domestic buffalo was introduced to Europe as livestock. On this continent it developed landraces that have adapted to the climate here, including a dense and effective winter coat. They can cope with temperatures below -20°C and are also resistant to European parasites. In fact they are better at living on very poor forage than cattle are. While there is a number of specific named breeds in Asia, most buffalo in Europe are of mixed, undetermined origin and there are no clearly marked breeds. I am not that keen researching all those subtypes/breeds of domestic buffalo as it is not really relevant for this post.

It is estimated that there are about 150 million domestic buffalo on this world according to Wikipedia, most of them in Asia. These include a number of feral populations in South East Asia, and also Australia. The longest history as European livestock they have in Eastern Europe, especially the Balkan and also the Carpathians. But they also become  increasingly popular in Germany where they number 2.100 animals already (2010) [4], and also the Netherlands. They can spend all year round outside without a barn or shed and supplementary feeding so some conservation projects use them as grazers just like cattle or horses. Why do they use this non-native species?

Water buffalo at the NP Neusiedler See-Seewinkel, Austria.

Water buffalo as European megafauna?

Obviously domestic water buffalo can be used in conservation projects, but in order to see whether they should be used, or even be introduced into wilderness areas, or not we should investigate the following questions:

1. What purpose do water buffalo serve in conservation projects?

2. Could this job be done by native species as well?

3. Are domestic water buffalo an adequate proxy for B. murrensis, could they even be regarded as native themselves?

Water buffalo have the same positive effect on flora and fauna diversity that other grazers have. By feeding and trampling, they create a more diverse landscape by hindering single, few species from becoming over-dominant and reducing the amount of plant and animal species present. Their organic waste is habitat and food source for many insect and decomposer species, which, on the other hand, are important for avi- and herpetofauna. But they have one advantage over cattle, horses, sheep and goats: the water buffalo has the highest affinity to wetland, both in physical and dietary respect [4, 5]. by wallowing they create small bodies of water that are important for amphibians, as they experience habitat loss even in nature reserves because of silting and drying. Especially the endangered yellow-bellied toad (which is in fact not a toad) benefits from this, but also a lot of other species as well. Cattle and particularly wild boar (as everybody knows, they wallow as well) do that too, but not to the same extent. And cattle make only limited use of wetland, as do goats and sheep. Cattle cannot digest a number of water plants in the first place [4.]. Elk have been used in wetland conservation with success, but they are browsers and do not prevent the unwanted succession of grasses [4].

That is the reason why conservationists have to artificially create these small, non-persistent waterbodies, by using trucks or even tanks (f.e. see here in the Lippeaue) [5]. No question that this is not a satisfying solution on long-term sight for reserves should be as natural as possible. Water buffalo consume wetland or water plants that none of the other species do, and are most efficient in creating small waterbodies by wallowing and trampling. So perhaps water buffalo are not only good but almost necessary for many European nature reserves and biotopes containing wetlands [4, 5].

But if that was the case, how did all this diversity survive all the millennia of the absence of Bubalus? What did amphibians and waterbirds do before we had the idea of using water buffalos or tanks in natural reserves? I think that the work of cattle/aurochs (and also other large grazers), wild boar and elk, not to forget the dynamics of natural waterbodies, were sufficient to keep up the diversity up over the Holocene. In fact, it was and is the industrialization and water management that is destroying the habitat of amphibians and other wetland dwelling species and not the loss of a keystone species several millennia ago. So in my view, the use of water buffalos is certainly beneficial, but not indispensably necessary.

Another argument raised by those who advocate an introduction of water buffalos into European nature reserves is that domestic water buffalos have a legitimation as native animals here because their genus, Bubalus, was present here until the Pleistocene extinction wave and that they would be present without human influence anyway because either B. murrensis was hunted to extinction or B. arnee would have migrated to Europe if humans would not have hindered them [6]. In my opinion, it is speculation that B. murrensis was hunted to extinction. While I am convinced that the overkill hypothesis is certainly more plausible than any other in cases such as the woolly mammoth, and that way more Pleistocene megafauna species would still be alive today without human influence, I think it is too much of a stretch to blame humans categorically for the extinction of each single species that died out around that time – a time that undoubtedly also experienced massive climatic and ecologic changes. And the poor presence of Bubalus in Pleistocene art makes me think that it probably was not a very important game species to humans. Of course it is possible that Bubalus survived longer into the Holocene but and that we did not notice that in archaeological evidence because most of the Holocene Bubalus material has been assigned to Bison and Bos. But where are the crania, or at least horn fragments? One argument is that water buffalos died out earlier than the other two bovine species because human settlements focused on large fertile deltas, the prime habitat of Bubalus. However I have no doubt that there would have still been enough space for this species to continue living into historical times and I also do not think that civilization was intense enough to prevent Bubalus arnee to migrate into the west and, in consequence, Europe.

Nevertheless, lets assume that Bubalus murrensis would have still been around in Europe without human influence and it therefore has a legitimate place in modern European nature reserves. Would domestic buffalo be an adequate proxy? I do think so. They are not the same species (the claim that B. murrensis was merely a chronospecies is, as far as I know, baseless), but ecologically and morphologically probably very similar. Despite being domestic, they are as suited as most cattle to live here in a feral state.

In the end I would say that calling Bubalus a native clade in modern Europe is far-fetched,  and regarding domestic buffalo based on very weak ground as B. arnee probably never inhabited this continent. Actually it sounds like a classic non sequitur: “I am in Innsbruck. Innsbruck is located in Austria, just like Vienna. Therefore I am in Vienna”. Nonetheless, water buffalo can live here, perhaps would without human influence or perhaps not, and they would probably do no harm if introduced here (I do not think they would be considerable competitors for other grazers) but would actually be beneficial even though probably not necessary. Imagining a wilderness area with three bovine species instead of two that all look rather different from each other is tempting and inspiring, and it would be interesting to see how these three species would interact, ecologically and physically. Therefore I would certainly have no objections against a project releasing water buffalos into a European reserve, although I think Europe can do well without them and truly native species should have priority in any case.

The public acceptance of feral water buffalo would probably be higher than the academic.

The water buffalo project of the TNF

The True Nature Foundation is currently preparing a project that aims to introduce water buffalo into a number of suited areas [7]. The plan is to build up herds of European domestic buffalo that are adapted to live here in a feral state and to inseminate them with semen of wild Asiatic buffalo in order to create a buffalo population with wild-type features but also adaption to European climate parasites and forage at the same time. Sounds like an ideal plan to me and I actually had the same idea as well. They also claim that they want to reconstruct the physical characteristics of the Bubalus murrensis, but I wonder how that should work. We have no idea of its colouration, whether it had those white markings or was solid coloured, and if in which tone (grey like Asiatic buffalo or dark brown to black like European domestic buffalo?). It is likely that it had the “standard body” of water buffalo with the same size as B. arnee, which is of course feasible to achieve but not a characteristic trait of B. murrensis. The only diagnostic optical trait of this species we know of is its horn shape, which is, as I described above, more like that of the tamaraw than of any domestic or wild Asiatic water buffalo. Therefore I suggested also using semen of tamaraw. I think it is likely that both species hybridize without restricted fertility and it would bring in the genes for a murrensis-like horn shape. Also it would add more genetic diversity and other wild-type genes. The colour of that population would be a bit of a mosaic, but by far not as heterogeneous as in a random bunch of domestic cattle.

What’s the good of trying to create optic similarity? Well, its not a functional one. Actually it is merely an emotional one, it is more satisfying when the animal that is supposed to fill the old niche of B. murrensis also resembles this species appearance, even if this resemblance is only superficial and artificial.

 

The crossbreeding that will be executed by the TNF's project. Looking forward to seeing the results.

But why using a population of hybrids instead of pure herds of wild Asiatic water buffalo? First of all, it is not sure at all that they would do well in Europe. They are from a different climatic zone with different parasites and diseases. Furthermore, and that brings as to the next point, wild Asiatic buffalos are very rare and endangered, and there are only few populations left in the wild. So I doubt that owners would give their animals to such a project introducing them into a climate and region where they are not native – and I completely agree on that. In my opinion, and probably that of most other people as well, the few true wild water buffalo should be used for conservation programs in their home range. So taking a herd of domestic buffalo and inseminating them with wild buffalo sperm is the most ideal option to me, also because the domestic buffalos are adapted to Europe already. I don’t think such a population would be unsatisfying. For once, most people would not know that a domestic water buffalo is domestic, since it does not nearly look as domestic as ordinary cattle do. Furthermore, they would inherit wild traits anyway and the herd would not be very heterogeneous.

Behaviour

We know nothing about the behaviour of B. murrensis, especially towards humans. Actually I am not fond of the issue that is always made of this aspect of the behaviour of bovines in nature, but it has to be addressed because people are concerned about that when these animals are to be released. The behaviour of wild Asiatic buffalo is described as aggressive when teased but preferring flight. So “standard” for wild bovines. Domestic buffalo are said to be very gentle and friendly in normal domestic use. But very likely their behaviour is plastic and depends on socialization just like that of cattle I guess, so their mood might change when living under semi-feral conditions. I visited the National Park Neusiedler See-Seewinkel in Burgenland, Austria, in 2013 where Hungarian Grey cattle graze together with water buffalo. The buffalo were very curious and cuddly. One of them showed threating behaviour but probably because they had calves. I never heard or read that water buffalo are problematic because of aggressive behaviour, so they probably are not any more dangerous or not-dangerous than cattle under semi-feral conditions.  

Water buffalo and cattle live together in some semi-natural reserves like in Neusiedl or Spreeaue (Germany), and there is, as far as I know, no agonistic behaviour between both species. Bos and Bubalus do not hybridize, a mating either results in no embryo or a miscarry at early stage [8], so there is no danger of intermixing. Probably not with wisent either, because Bison is way closer related to Bos than Bubalus.

Legal issues

Domestic buffalo are legally treated in almost the same way as domestic cattle. I don’t know what the situation with wild Asiatic buffalo is, since these are wild and exotic animals. It is probably also an interesting question how a hybrid population of wild and domestic buffalo will be treated… Let’s see what the TNF is going to do about that.

Literature

1. Pucher, Erich: Erstnachweis des europäischen Wildesels (Equus hydruntinus, Regalia, 1907) im Holozän Österreichs. 1991.

2. Schreiber, Dieter: Finds of Bubalus murrensis (Bovinae, Mammalia) from the Upper Rhine valley: a focus to the complex sedimentological conditions of a quaternary fluviatile system. 18^th International Senckenberg Conference 2004

3. Kumar et al.: Mitochondrial DNA analyses of Indian water buffalo support a distinct genetic origin of river and swamp buffalo. 2007.

4. Wiegleb, Gerhard; Krawczynski, Rene: Biodiversity management by water buffalos in restored wetlands. 2010.

5. Stumpf, Thomas: Machbarkeitsstudie zum Einsatz von Wasserbüffeln in der Landschaftspflege im Rheinland.

6. Krawczynski, Rene: Visioning feral water buffalos for Europe.

7. Webpageof the TNF

8. http://www.yakzucht.ch/downloads/domes_genetik_rind.pdf