( ( ( 4-chambered heart ) ( of ( ( mammals and ) birds ) ) ) ( ( ( are not ) homologous ) . ) )
(ROOT (S (NP (NP (JJ 4-chambered) (NN heart)) (PP (IN of) (NP (NNS mammals) (CC and) (NNS birds)))) (VP (VBP are) (RB not) (ADJP (JJ homologous))) (. .)))
4-chambered heart of mammals and birds are not homologous.
(ROOT (S (PP (IN Like) (NP (NP (DT all) (NNS tetrapods)) (PP (IN except) (NP (NNS birds) (CC and) (NNS mammals))))) (, ,) (NP (NNS frogs)) (VP (VBP possess) (NP (NP (DT a) (NN heart)) (PP (IN with) (NP (CD three) (NNS chambers))))) (. .)))