I’m not talking about the neighbours dog that eats horses but a truly big dog.
Think of it this way:
Lion/Tiger is to cat as
?? is to dog
I know that no such beast exists in our modern world but has there ever been a lion-sized canine and if not, why not? Such an animal would surely be a fearsome predator with strong jaws and good stamina as well as sprint speed.
And I thought it was just the title to a Grateful Dead song until I saw the fossils in a museum.
A pretty impressive beast but not nearly on the same scale as the large cats. I wonder why felines grew to such impressive sizes in the past (sabertooth) and in the present but canines remained relatively small.
Wow, I just saw that skeleton display and thought to myself “that’s in New Mexico”. Sure enough it is. I was at the museum once. In 1992. For 20 minutes.
But where are the Dire Badgers? 
The Pyrenean Mountain Dog is pretty big, as is the Great Dane
A little selective breeding and one could have a monster.
(we used to have a Pyrenean a few doors away, it would stand up with its paws on the shoulders of its 6’ owner - the front legs were horizontal)
Some cousins of my wife have one of those and believe me, next to the family’s poodle that thing is as big porportionally as a lion is to a domestic cat. A Pyrenean puppy is the size of a full-grown beagle! :eek:
Some wags as to why a big dog never really deveolped. Large size goes against their natural advantages such as:
Packing, the general idea here is surround a big beast with a bunch of you smaller beasts, kill it and you all eat well. This also allows a ‘pecking’ order to be established, as even the ‘bottom dog’ gets something. If dogs are much bigger, first the pack hunt means that the kill won’t feed you all, breaking down the dog ‘society’ as the bottom dogs will no longer stick with the pack as they won’t get anything to eat there. They will also be big enough to hunt w/o a pack. Perhaps if bigger game deveolped then dogs can ‘grow’ to take them down, but this could also just lead to larger packs.
Cats are sprinters, while dogs are long distance runners. Hauling around a lot more mass would be counterproductive to their long distance advantage. To go from a lean and mean animal that is used to very long chases to a hide and pounce muscle bound animal requires many steps to achieve, including change in thinking. In such a evolutionary transition there is not much to eat along the way - till you get to the bigger ‘cat’ style dog.
Cats have also evolved to be near silent hunters, which is a big advantage when taking down large game. Retractable claws allows the cat to walk with almost no noise, cats have also learned to walk on the furry tops of their paws to make the final apporach even more silent. Again this level of dexterity seems to go against their current long distance runner mold, so I don’t see this developing till the transition is near complete.
Perhaps the “large dog” ecological niche has already been taken by bears?
I just have to comment on this section of your article, re: the tooth
That’s the best river name ever. I bet there’s a great story as to how that one got named!
Gonna go with kanicbird’s theory that it’s because dogs (and their rather large relatives, Wolves), travel in packs, while felines tend to be somewhat more solitary in nature (though they also form communities under some circumstances). Not only would having a pack of bear-sized dogs make finding enough food very difficult, but since they are in a pack, they don’t need to be as large.
Now, HERE is a good question for you: What did wild chihuahuas hunt before they became domesticated? Cause I’ve got a hillarious mental image of 20 of them taking down a goat.
“600 pounds of sin.” … it probably actually made for a better song in that Robert Hunter didn’t really know anything about Canis Dirus, which was only slightly larger than a modern day wolf. An entry from Hunter’s journals from the annotated Greatful Dead site:
Not actually a canid, but you might consider the amphicyon as close, since it is often called a “bear dog”:
http://www.amnh.org/exhibitions/permanent/fossilhalls/vertebrate/specimens/amphicyon.php
Amphicyons.
This rendering looks rather dog-like:
http://www.flmnh.ufl.edu/fossilhall/FLPaleo/ThomasFarm/Amphicyon.htm
While this one looks like the critter was on drugs, or at least in a perpetual state of confusion:
http://big_game.at.infoseek.co.jp/bear/Amphicyon.jpg
I prefer the ones appearing Julian May’s Pliocene Exile stuff.
Whether they were closer to bears or dogs, they were damned big, anyway.
As others have noted, dogs are social animals and pack predators; larger size gives a relative competitve advantage to the individual but isn’t beneficial to the group (as it requires more food per individual). With pack hunting, there’s no need for an individual animal to be as large, have as much endurance, or be as strong as even the largest prey; the group’s capability is an aggregate.
Solitary or pair hunters like the big cats need to be stronger and faster, if not strictly larger, than their prey. This can be an evolutionary trap where they end up winnowing out the slower and weaker members of the prey species, thereby inadvertantly creating a selective pressure for faster and more agile prey, and forcing the predator species to improve or die off as well. It also results in their being apex predators that are small in population and sensitive to changes in key prey species. Whereas dogs or hyenas will prey or scavange both large and small species efficiently, a large cat can’t make an effective meal out of small rodents, and can die off during lean times.
Bears and bear-like creatures aren’t strictly relevant because a) bears are solitary, typically nonsocial animals, and b) all extant bear species except for polar bears are not primary predators; they’re omnivore scavengers who will display hunting behavior only opportunistically. The extinct short-faced bear was probably the most predatory of all sub-arctic bears (and would in fact prey on brown and black bears), and the Kodiak, a subspecies of brown bear, will fish during salmon spawning season, but neither is a strict carnivore, despite their inclusion in order Carnivora.
The Dire Wolf wasn’t much larger than the modern grey wolf, which is admittedly a large dog, but not lion-sized. There are limitations to the general physiology of Canidae that would seem to argue against attaining a large (several hundred pound) mass without significant novel mutation. [thread=368823]Here’s[/thread] an old thread which discusses size limitations of species.
Stranger
However you have to admit that those things are interrelated. You can evolve into large size or you can evolve pack hunting or you can evolve one and then the other. They’re independant evolutionary advantages. Presumably dogs always were pack hunters hence any mutant large dog was at a disadvantage since it had to eat more but did not gain any advantage from being bigger.
Although I do not know if size of prey is all that related to size of the predator. Just consider the weasel that has been known to bring down bunnies or the whales that eat plankton. Large wolves can and do survive alone so it’s not too much of a stretch to imagine a canid that is not a pack hunter.
True, and as a counterexample to my own argument, foxes are mostly solitary hunters, and yet foxes as a class (both the true foxes of genus Vulpes and other members of Canidae commonly known as foxes) are the smallest of all canids. But there doesn’t seem to have been any selective pressure for the large size and hunting prowess of the big cats. This may be partially due to the typical large litter size of canids (making them too prolific to be so large) or the traditional ecological niche of canids as scavengers, pack hunters, and small game hunters, which favors a predator that is adaptable and can survive population fluctuations. That’s a bootstrapping argument, to be sure, but with natural selection you never start with a blank slate; you’re constantly expanding from the capabilities and pressures you already have. It’s worth noting that while virtually all members of subfamily Pantherinae are threatened or endangered (and many other large cats are extinct), most canid species (except for the big wolves) continue to survive and often thrive, even in the face of urban and agricultural development.
So, being relatively small and adaptable has worked out pretty well, evolutionarialy speaking, and that’s the only criteria Mother Nature ultimately grades on. The big cats did okay in the era of large land herbivores, but small-to-medium dog-type creatures seemed to have acquitted themselves in their own respective niches far more effectively.
Stranger
Amendment: But there doesn’t seem to have been any selective pressure on canids to select for the large size and hunting prowess of the big cats.
Stranger
Why are you looking for an analogy between dogs and cats, as if there’s some natural connection between the two, other than that we keep them as pets? Why not dogs and sheep? Cats and bears?
The largest canid that is not a pack hunter is the Maned Wolf of South America.
One thing to take into consideration is that a very large, solitary canid would essentially share its ecological niche with bears. Since bears already exist, it may be difficult to evolve into that niche. The only place where canids have not historically overlapped with bears is sub-Saharan Africa, where the pack-hunting Spotted Hyena, larger than any extant canid, also occurs.
