I support those who say Ramanujacharya as avatara of sankarshana (Adishesha)sankarshana (Adishesha).
Avataras are 2 kinds, poorna (complete) avataras and amsha (partly) avataras. Ramnuja, Shankara comes into 2nd category avataras.
There is a proof for this in his biography. When he was answering the questions asked by thousands of pandits simultaneously from behind a veil. One of the pandits gets curious to know how he is able to answer thousands of pandits simultaneously without any difficulty peeks inside the veil and finds a thousand headed snake which is nothing but Adi Shesha himself. :)