AFAIK, nobody claims that humans are superior because we stand on two legs. Nobody says that bears, for example, should be given partial human status because of their occasional use of two legs.
The claim of human superiority is based instead on our superior intelligence(1). For example, dogs will do anything within their power for a pack member. But they can’t generalize, AFAIK, and decide that somebody they don’t know deserves protection because they count as “pack”. Dogs communicate emotions very effectively, but they don’t communicate ideas. They don’t abstract.
Note that unless you believe in the ideal of the übermensch, which I do not, superiority does not mean the right to abuse. Abusing dogs isn’t a bad thing because we are not superior, but because we are and we are capable to realizing it is a bad thing.
h/t (meaning I got this meme from) Lori Trentanelli
(1) Also, for many people, on free will. However, given the inability to prove humans have free will, or that dogs lack it, this cannot be used as an argument IMAO.