( ( ( The condition ) ( ( in which ) ( ( the ( middle ear ) ) ( has ( ( three bones ) ( linking ( ( the ear ) ( drum ( to ( the ( middle ear ) ) ) ) ) ) ) ) ) ) ) ( ( is ( what ( defines mammals ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN condition)) (SBAR (WHPP (IN in) (WHNP (WDT which))) (S (NP (DT the) (JJ middle) (NN ear)) (VP (VBZ has) (NP (NP (CD three) (NNS bones)) (VP (VBG linking) (S (NP (DT the) (NN ear)) (VP (VB drum) (PP (TO to) (NP (DT the) (JJ middle) (NN ear))))))))))) (VP (VBZ is) (SBAR (WHNP (WP what)) (S (VP (VBZ defines) (NP (NNS mammals)))))) (. .)))
The condition in which the middle ear has three bones linking the ear drum to the middle ear is what defines mammals.
(ROOT (S (NP (DT The) (JJ mammalian) (JJ middle) (NN ear)) (VP (VBZ has) (NP (CD three) (NNS bones))) (. .)))