Though you shared a common ancestor with your dog or cat around 100,000,000 years agocitation required, most genealogists (and state laws) agree that it's not proper for individuals to claim parenthood of their pets.
One solution: Pet event
The simple thing to do is just to create an Pet event on your tree. Add a picture of the pooch, kitty, hamster, or donkey with the duration of the pet's time with you (1994-2006), and all family members who lived with the pet.
Another solution: Pet pedigree
A more complex, but full featured option is the following:
- Create a tree for your pet. Using a free email service, create an email address for your pet, and build its tree. You can even add its pedigree, pictures and events--basically, whatever you want.
- Add your pet as a friend
- Create an event on your tree that includes the date of adoption, etc.
You can then add your non-human friend to your family group.