Echoing the sentiment of everyone else here, pets are fair game for thanking in dedications, acknowledgements, or where ever you like.

Not only have I read books where pets are in either, or both, but I think I remember reading somewhere that the vast majority of the human race owns or enjoys the company of a domesticated animal of some sort. Heck, on my flight home the othe day, a guy was doing coochy coos to a bird! LOL