( ( ( ( ( ( They ( mostly ( have ( four limbs ) ) ) ) but ) ( ( some ( aquatic mammals ) ) ( ( have ( no ( ( limbs or ) limbs ) ) ) ( modified ( into fins ) ) ) ) ) and ) ( ( ( the forelimbs ) ( of bats ) ) ( are ( modified ( into wings ) ) ) ) ) . )
(ROOT (S (S (NP (PRP They)) (ADVP (RB mostly)) (VP (VBP have) (NP (CD four) (NNS limbs)))) (CC but) (S (NP (DT some) (JJ aquatic) (NNS mammals)) (VP (VBP have) (ADVP (RB no) (NP (NNS limbs) (CC or) (NNS limbs))) (VP (VBN modified) (PP (IN into) (NP (NNS fins)))))) (CC and) (S (NP (NP (DT the) (NNS forelimbs)) (PP (IN of) (NP (NNS bats)))) (VP (VBP are) (VP (VBN modified) (PP (IN into) (NP (NNS wings)))))) (. .)))
They mostly have four limbs but some aquatic mammals have no limbs or limbs modified into fins and the forelimbs of bats are modified into wings.
(ROOT (S (NP (NNP Birds)) (VP (VBP have) (NP (CD four) (NNS limbs))) (. .)))