I greatly appreciate you taking your time to help me out with my questions and lastly I would like to ask what are the original 3 pets?

Hi I am sort of new to world of war craft and recently started collecting pets. I joined this site to hopefully get some tips or advice to pet collecting. I am currently working on collecting from the dragonkin category, but I see that some pets I can't obtain? For example an onyxia whelpling. How d...