( They ( ( ( are mostly ) ( ( large species ) ( living ( ( ( in ( the ( open ocean ) ) ) ( rather than ) ) ( on ( the ( sea bottom ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBP are) (ADVP (RB mostly)) (NP (NP (JJ large) (NNS species)) (VP (VBG living) (PP (PP (IN in) (NP (DT the) (JJ open) (NN ocean))) (CONJP (RB rather) (IN than)) (PP (IN on) (NP (DT the) (NN sea) (NN bottom))))))) (. .)))
They are mostly large species living in the open ocean rather than on the sea bottom.
(ROOT (S (NP (NP (DT The) (NN majority)) (PP (IN of) (NP (NNS species)))) (VP (VBP live) (PP (IN in) (NP (DT the) (NN ocean)))) (. .)))