( ( Most amphibians ) ( ( ( ( have ( four limbs ) ) , ) ( except ( for caecilians ) ) ) . ) )
(ROOT (S (NP (JJS Most) (NNS amphibians)) (VP (VBP have) (NP (CD four) (NNS limbs)) (, ,) (PP (IN except) (PP (IN for) (NP (NNS caecilians))))) (. .)))
Most amphibians have four limbs, except for caecilians.
(ROOT (S (NP (NNP Birds)) (VP (VBP have) (NP (CD four) (NNS limbs))) (. .)))