( ( ( ( ( Usually ( heart ( is three-chambered ) ) ) , ) but ) ( is ( ( four chambered ) ( in crocodiles ) ) ) ) . )
(ROOT (S (S (ADVP (RB Usually)) (NP (NN heart)) (VP (VBZ is) (ADJP (JJ three-chambered)))) (, ,) (CC but) (SQ (VBZ is) (NP (NP (CD four) (NN chambered)) (PP (IN in) (NP (NNS crocodiles))))) (. .)))
Usually heart is three-chambered, but is four chambered in crocodiles.
(ROOT (S (NP (EX There)) (VP (VBP are) (NP (NP (CD three) (NNS chambers)) (PP (IN in) (NP (DT an) (NN amphibian) (NN heart))))) (. .)))