I don't think there will only be pets in the afterlife. I think all animals will be there, if there are any animals at all.
I mean how just would that be for God to exclude all the other animals who were not pets?
Think about how animals suffer in the wild. I believe they deserve a recompense in the afterlife.
I do not believe, like some other religious believers, that animals are only here for humans to enjoy and use for their benefit while they are alive. I believe that animals exist in their own right. This idea that only pets will go to heaven because humans need them to be there is so egocentric.