The curled tails in dogs is a result of selective breeding by man. This feature is not found in wolves, foxes and other canine type species. The domestication and breeding of foxes in Siberia for the fur industry has show similar trends in the later generations of foxes, just like dogs. The genes are apparently there, but not expressed in the wild............
Perhaps pack dogs don’t need curly tails because they have each other to keep warm, whereas the solitary dogs (pets) need them. Give me a gold star for trying? LOL