Not at all. At the contrary, they had a very large area of existence, covering large parts of Africa, Europe and Asia, and very different climates. We just killed them off almost everywhere over the course of history.
Yeah forget the 550 lb dog, I want a pygmy lion. Feline pets that have pack instincts would be great. I want a cat that behaves like a dog (well actually inbetween, not quite so enthusiastic as a dog)
This is a cause that I can enthusiastically get behind. Put me down for a miniature bengal tiger 
It looks to me that the Epicyon as part of the Borophaginae subfamily is further from dogs then the foxes are. To the best of my knowledge Dogs and Foxes can’t interbreed even with artificial insemination. So I don’t think the Epicyon can be used as an example of potential domestic dog size.
Look into the Savannah Cat then, they are largish (20 lbs or more) but tall, thin and long and dog-like in description.
[QUOTE=wiki]
The cats are commonly compared to dogs in their loyalty, and they will follow their owners around the house like a canine. They can also be trained to walk on a leash and to fetch.[4]
Some Savannahs are reported to be very social and friendly with new people and other cats and dogs, while others may run and hide or revert to hissing and growling when seeing a stranger. Exposure to other people and pets is most likely the key factor in sociability as Savannah kittens grow up.
[/QUOTE]
See post 14 for the context of why I posted that.
OK, fair enough. I thought as you quoted my post about the dire wolves, you were saying there was a canine larger than the dire wolf that were still wolves.
Also I did some digging, there seems to be claims of Dog-Fox hybrids (Doxes) having been born but no genetic proof at all. Additionally the chromosomes are so different that even if successfully brought to term the offspring will be infertile.
You can do a lot with unlimited time and money. If you simply created a huge artificial island, or terraformed Mars, populating it with nothing but plants and dogs, over several million years, there’s a good chance they would diversify to fill common niches, including giant super-predator, without further human intervention.
Selective breeding over more comprehensible timescales would run into the sorts of difficulties mentioned by previous posters. That said, presumably our knowledge and technological capabilities would be advancing at the same time. Is direct genetic tampering forbidden? It could potentially make things much easier.
Bottom line is, yes, but it might take a while, and might not be considered a ‘dog’ at the end.
We really don’t know enough about the genetics/growth and development of dogs to know how hard it would be. Weisshund pointed out some of the difficulties, and there may be lots of others we don’t know about. Remember, any changes have to work in the context telling cells in a developing embryo what to do; it’s not just changing a size on a blueprint. And then added to that is the difficulty of avoiding negative variants in a small inbred population.
But, sure, eventually, with a large enough population, after some unknown number of generations, you could get something descended from dogs that weighed 500 pounds. I mean, every 500 pound animal alive today descended from a single-celled animal, so it’s clearly possible. With enough time.
But it’s probable that whatever you got at the end would be different enough from it’s dog ancestors that objective observers would consider it a different species-- just like the 500 pound animals alive today are different species than whatever 50 pound ancestor they had.
If the objective observer was a biologist, he’d be using the Biological Species Concept. If it could breed with other dogs, there would be no reason to consider it a different species. As a domesticated animal, the Biological Species Concept wouldn’t consider any other criteria. It’s only in the wild that the issue of whether a population regularly interbreeds with another population makes sense, and domesticated animals don’t live “in the wild”.
If anyone knows dogs it’s weiss hund.
Yup, the amazing thing is the already existing size variety in the species canis lupus resulting of huge human imposed selection pressures which we discussed from the other side once wondering why there are not miniature cats as there are dogs. In this post, I linked to an article explaining how the huge range in dog size is apparently related mostly variation at the IGF-1 locus.
Rickjay, given Oakville’s animal control by-law 2010-157 s. 9 (a), you should consider getting a big, not so fluffy bobcat for when you start breeding humongous dogs.
A 500 pound dog is essentially a bear.
The skeletal structures of a dog are very poorly designed to support great weight, and breeding one to great size (indeed, if you even could) would make for a fragile, short-lived, unhappy beast. Legs, ankle/wrist joints, paws, pelvic structures, and spine would all need to be altered. You’d do better to try and breed dog-like characteristics into a bear. Not that any such project would be a good idea, either.
(I know, but I loved seeing Sarah McLachlan in the spot!)
I suspect some country will get around to it, maybe starting with something like this:
Check out the super-whippet.
Devolution? Whippet good.
The problem is that evolution is slow. An animal changes in response to changes in it’s environment - food source, enemies, biosphere… With each specific change, some adaption then follows and if it is slow enough, the details of the animal’s anatomy have time to catch up.
Consider the adaptions that allow a giraffe or elephant to exist. Ad each became taller/heftier, the ones that survived had the better adaptions to that feature. Giraffes have amazing adaptions to extreme height (i.e. blood pressure system to supply the head), elephants have amazing adaptions to size - i.e. thicker skeletons, feet that can support the weight, pelvis, even big ears to shed body heat.
With every adaption comes a cost. Specifically, with forced breeding, you are ignoring many other characteristics to force a single one - speed for racehorses, or in your case size for dogs. This means that you risk “breeding out” desirable characteristics while concentrating on the one you are chasing. Plus, being domesticated, there is no “natural” selection to help maintain certain characteristics. So let’s say you breed out smarts. You end up with a huge, dumb out-of-control 500-lb carnivore, that lost the ability to be trained. What could go wrong?
Yep I know about Savannah cats. There’s not many breeders and I haven’t been able to find a breeder in my part of the world.
Except when it’s not. That is not to say that punctuated equilibrium posits new species arising in the blink of an eye, but depending on the environmental changes and whether or not populations get isolated, evolution can vary tremendously in speed.
This. ^^
I’m a member of the Shiloh Shepherd Breed community, and even with relatively modest goals (better hips, elbows, & heart; increased size; less-intense temperment), we’re walking a razor edge between gaining desireable characteristics and losing other desierable characteristics.* The Genetics Task Force has a heavy load, and disagreements on course of action constantly fragments the community.
Breeding a monster dog would face similar challenges, and many more, as you started pushing the limits of what the basic platform (C. l. familiaris) can naturally support.
*the consequences of which lie near my feet right this instant - A physically magnificent dog with serious temperment faults.