Why weren't there any "big dogs," like "big cats" are?

Cats have lions, tigers, jaguars, etc and other big cat that are extinct. Why weren't there any big dog types, the dogs are bigger on average than a typical cat. Was it because the dogs hunted in packs so they did not have to get as big as the solitary cat hunters? But that does not explain lions.

Why weren't there any "big dogs," like "big cats" are?
There are "big dogs" the Wolves. A Gray Wolf's (the largest wolf species) average length of an adult female gray wolf is 4.5 to 6 feet; adult males average 5 to 6.5 feet. The average height (at the shoulder) of a gray wolf is 26 to 32 inches.





Though smaller in length compared to a Siberian Tiger (the largest of the "big cats") who can grow anywhere from 10 feet to 12 feet long. A gray wolf though is about as long as a female lion, though may not weigh as much.








So in all reality the Grey Wolf is what would be referred to as the "big dogs" along with all the other species of wolves. Though they hunt in packs it doesn't mean that they indeed aren't the 'big dogs" of the world.
Reply:The real question should be, why aren't there any "small dog" species? (Actually there are - foxes.) The domestic dog is derived directly from the wolf, and some dog species are considerably larger than wolves - for example, St. Bernards and Great Danes.





Maybe the reason why there aren't any "big dogs" is just the way the evolution cookie crumbled.