To be clear, they're not actually classified as the same species. Canis Lupus and Canis Domesticus are both Canids, but are not considered to be different species. The thing is that a purely genetic study shows that they're almost indistinguishable. There isn't enough difference to mark them off as a different species.

The genetic difference isn't there, but the functional difference is. Their instincts and behavior are different, as is their relationship with us.

I'm not sure about felines, but I do know that you can crossbreed several of those species, as well. Lions and tigers can produce viable offspring (generally called tylions, even though lyger is a much better name). And some very stupid people a few years back started crossbreeding housecats with bobcats to create an exciting new exotic pet. I believe the fad died down when people realized that wild bobcats don't like humans and generally try to maul them.

As for dog breeds, try The American Kennel Club. They have a pretty good guide to the officially recognized breeds. And I believe they're even starting to accept some of the more popular crossbreeds like labridoodles.

Anyway, glad you enjoyed the post. Thanks for commenting. :) (And glad I saw the notification in my LJ inbox. Notification email never came!)