Possible Breeds to be Used in the Creation of a Proxy for the Yukon Wild Horse

The Yukon Horse 

The Yukon horse (Equus (ferus) lambei) was a pony-sized equid that inhabited the northern parts of Canada and Alaska until approximately twelve thousand years ago, when it was presumably hunted to extinction by newly arrived paleo-natives. Thanks to relatively plentiful frozen and fossil specimens, more is known about it's diet and appearance than other North American horse species. For example, it is known that it had roughly the same colouring, size, and body conformation as the extant Przewalski's horse (Equus ferus przewalski). However, there are some notable differences in colouring and fur qualities. Like Przewalski's horses, the Yukon horse was dun coloured with a dorsal stripe and other primitive markings, but where Przewalski's horses have short, rigid, black manes, somewhat akin to a zebra's, the Yukon horse had a mane much more similar to that of domestic horses. The main was long and flaxen, and according to preserved animals, blonde. These horses also had a very thick winter coat that would have allowed them to survive in the same Arctic conditions as mammoths, muskoxen, bison, and reindeer. They would have served an important ecological role as prey animals, fertilizers, and removers of snow and heavy grass, helping to control and remove the insulation layer over the permafrost. 

Takhis 

While the obvious solution might be to use Przewalski's horses as unaltered proxies for the Yukon horse, it is in actuality not the best or most practical solution. Takhis, as Przewalski's horses are sometimes called, are not as well-adapted to cold conditions as some of their domestic cousins are, and might prove unable to survive in the Canadian Arctic. However, as the only true wild horse remaining in existence, it is desirable to preserve some of their wild behaviour and physical traits in any feral horse population. As far as their use in the Yukon Horse Project (not an official name or institution, but sounds cool), their contribution would be limited to occasional inseminations of project mares using material from takhi stallions shipped overseas or from North American zoos. Their mane colour and coat features would have to be selected against, but their coat colour is acceptable. They are perhaps a little large as well, standing fourteen hands (approximately one point four meters) at the shoulder where the Yukon horse stood approximately twelve hands (approximately one point two meters). Smaller surface area compared to volume is an adaptation to cold weather, as are shorter legs, and so these are additional traits that should be selected for, along with small ears, large snouts, and large guts/organs. Takhi behavioural traits will be important as well, due to their never having been domesticated. They will not be tempted to approach humans and will have more appropriate reactions to predators, such as wolves, bears, and eventually, large cats. 

Yakut Ponies 

Perhaps the best candidate for a Yukon horse proxy is the Yakutian pony of northern Siberia. Regularly surviving temperatures as low as minus sixty degrees Celsius, and often living in semi-feral conditions, Yakut ponies are rumoured to have Yukon horse blood already, though that is in truth doubtful. However, their extreme climatic adaptability and wild nature make them ideal candidates for recreating the Yukon horse. Their height is good, standing at around twelve hands. Fur colour is varied, but the appropriate dun colour with primitive markings, as well as blonde, flaxen manes can be found commonly in the population. Their thick coat is particularly desirable for the project. Yakut horses are already being used in the Pleistocene Park project as proxies for west Beringian horses, and have been quite successful in excavating snow and controlling grass growth. 

Fjord Ponies 

Another good breed for possible use is the Norwegian fjord pony, a slightly larger, stronger breed. The fjord horse is a very old breed, being relatively unchanged for about ten thousand years. They are of particular interest to this project due to their colouring, which is very similar to that of the Yukon horse. They are also a cold-adapted, semi-feral breed that has retained many primitive traits. Their height is a little tall, at about fourteen hands.  

Icelandic Ponies 

The third and final domestic breed for possible use is the Icelandic horse. A smaller breed at twelve to thirteen hands, it is a similar breed to the Yakut horse, with a thick pelt and varied coat colouring. These horses are kept mostly wild in their homeland. The concern with this breed is that obtaining them from Iceland would be very difficult. 

Conclusions 

The Yukon Horse Project will be set up as an ongoing project in northern rewilding reserves. The best plan of action it seems is to start with a very large herd of maybe fifty mares, made up mostly of Yakut horses and perhaps a few Icelandic horses, all with dun coats and blonde manes. This herd will have one or two Norwegian fjord stallions added to the mix to control the herd and create a second generation. This herd will have occasional introductions of new animals as well as occasional conceptions of foals through artificial insemination by Takhis. Horses will be allowed to breed as necessary, and will be subject to natural selection. The only interference will be the occasional sterilization of animals with undesirable traits with colour or size. The environment will weed out animals that cannot handle the low temperatures. 

Further Reading 

http://www.tc.gov.yk.ca/publications/Yukon_Horse_2002.pdf 

https://www.rewildingeurope.com/wp-content/uploads/2014/09/Rewilding-horses-in-Europe-2014.pdf

Pictures

Yukon Horse Depiction - http://www.beringia.com/sites/default/files/Yukon-horse-banner.jpg

Takhi - https://foxstudio.files.wordpress.com/2008/11/takhi-berlin21.jpg

Yakut Pony - http://farm9.static.flickr.com/8691/17082533617_e5d7d25860.jpg

Fjord Pony - http://www.horsebreedspictures.com/wp-content/uploads/2015/10/Fjord-Horse-in-Snow.jpg

Icelandic Pony - http://bna-art.s3.amazonaws.com/www.bootsnall.com/articles/wp-content/uploads/2012/05/horses_iceland.jpg

Scimitar Cats and American Cheetahs: Homotherium and Miracinonyx

Apart from lions, and the surviving lynxes, bobcats, and cougars, Canada once had two other felid species. These were the scimitar cat (Homotherium serum) and the American cheetah (Miracinonyx trumani). The scimitar cat was a large, big-game predator found in the northern reaches of Canada and Alaska, and was a distant relative of the sabre-toothed cats (Smilodon). The American cheetah was a close relative of mountain lions and modern cheetahs, found on the great plains. 

The scimitar cat most likely went extinct as a result of large prey species going extinct, similar to the American lion. It would have been a major predator of large herbivores, such as mammoths, mastodons, and possibly ground sloths.  It was roughly the size of a lion or tiger, but was built more like a hyena, with slightly longer front legs than back legs. It also had long, serrating teeth meant for slashing the necks of large, thick-skinned prey. It's cranial, nasal, and legs anatomy suggest that it was a sprinting predator, adapted for quick ambushes at high speeds. 

Unfortunately a perfect proxy for Homotherium doesn't really exist. All of the sabre-toothed cats are extinct and modern felines are only distantly related. The truth is that a proxy for them would not really be necessary until elephants were present again. At that time, it is conceivable that lions would, like the scimitar cat, be able to control elephant populations by preying on calves. If a specific proxy were desired, perhaps Amur leopards (Panthera pardus orientalis) or Siberian tigers (Panthera tigris altaica) would be suitable. It's fair to say that Homotherium probably preyed on smaller prey as well, and having a large, cold-adapted predator would help in controlling numbers of deer and pigs. The tiger is closer in size to the scimitar cat, but the leopard is probably closer in habits and speed. If either of these cats were used, there would be concern for how they interact with other native predators. Siberian tigers are already sympatric with leopards, bears and wolves and might control numbers of either through competition and even predation. Tigers and leopards both are or have been found in the same areas as lions and lynxes. Lions have been found in the same places as cougars (Puma concolor cougar) in the past, though it is not sure how they interacted or whether having them in the same places as other large cast would cause problems  

The American cheetah, though similar in build to the cheetah, was more closely related to the cougar. Due to it's slightly larger size, it was probably not quite as fast as the modern cheetah (Acinonyx jubatus) but would have been the fastest predator present in Pleistocene North America. It is thought that the pronghorn (Antilocapra americana), which is much faster than any living North American predator, became the second-fastest land animal in the world in evolutionary response to predation by the American cheetah. 

Any of the cheetah subspecies could be used to control pronghorn and deer populations in the North American plains. The critically endangered Asiatic cheetah (Acinonyx jubatus venaticus) might be the variety best suited to inhabit the Canadian plains. This subspecies is suited to much colder, steppe-like conditions than it's cousins. However, there are as few as forty of them left in Iran, and so it may be much more practical to use any of the African subspecies. However if the situation was deemed extreme enough it might even be logical to take as many as twenty of the Asiatic cheetahs as a backup population so that they might be protected from the poaching, habitat loss, and traffic accidents that have endangered them. A breeding population could grow fast and be used as both a founding population for North America and a recovering population for the Middle-East and India. Genetic diversity would be low but genetic diversity has always been low in cheetahs as far as can be told.

Top to bottom: 

Homotherium depiction - https://retrieverman.files.wordpress.com/2010/04/homotherium.jpg

Miracinonyx depiction - https://blueline2011.files.wordpress.com/2011/11/american-cheetah.jpg

Siberian Tiger - https://upload.wikimedia.org/wikipedia/commons/b/b9/P.t.altaica_Tomak_Male.jpg

Amur Leopard - http://i1.wp.com/visitcryptoville.com/wp-content/uploads/2015/02/amur-leopard-in-snow.jpg

Asiatic Cheetah - https://upload.wikimedia.org/wikipedia/commons/7/72/Kushki_%26_rubit.jpg

Arctic Lions: Yes, really

Wild lions (Panthera leo) are today almost entirely restricted to Africa, the exception being the small population of Asian lions (Panthera leo persica) in Gir National Park in India. This was not always the case however, lions were in fact once found in every continent but Australia and South America. There were many lions in North America, including Canada. The American lion (Panthera leo atrox) was found in both arctic/taiga environments and plains/steppe environments.  

There is a lot known from fossils and DNA evidence about American lions. For example, it is known that they were significantly larger than modern African and Asian lions. This was presumably an adaptation to hunt larger North American herbivores such as bison and camels. From genetic evidence we know that it was more closely related to Asian and cave lions (Panthera leo spelaea) than to African lions, and so probably shared some characteristics with them. Asian lions have short manes compared to African lions, and cave paintings of cave lions seem to imply they did as well. From this it is supposed that American lions also had short manes. It is also presumed that like all modern lions, they had a pride structure with females being the hunters and males defending the pride from other males and dangerous creatures such as elephants and buffalo. It is not known exactly how their fur grew but presumably it must have been thick enough for them to withstand cold winters. 

Modern lions are not typically found in colder environments, but many captive ones are and have shown a surprising ability to withstand low temperatures. Many grow thick manes and pelts in response, with lions regularly being kept outside in the winter in places as cold as Scotland, Canada, and even Siberia. This adaptability is probably what allowed lions to have such a large range in the first place. It is thought that many of North America's large carnivores went extinct when many of the large herbivores were extirminated by human hunters. In the lion's case, this was the horses, the camels, and the bison. When the horses and camels were gone, and the bison few in number, the lions starved. Without the lions present the remaining bison could grow to the huge population size seen in history.  

If the lion's prey could be brought back to Canada, then supposedly the lion could be as well. The Pleistocene lions are considered subspecies of the lions still present today, so the differences are minimal. Substituting the American lion with lions from the old world should nicely fill the ecological role left behind by the American lion. The Asiatic lion from India might be the best choice due to it's closer relationship to the extinct lions, but really any lion subspecies would be acceptable, and African lions would certainly be more readily available. Lions could help to control native deer and bison populations as well as the numbers of species to be introduced later.

Picture comparing African and Asian lions (https://i.ytimg.com/vi/DAyaRfy8sPU/maxresdefault.jpg)