( Amphibians ( ( are ( ( ( ( the ( first ( true tetrapods ) ) ) , ) or ) ( vertebrates ( with ( four limbs ) ) ) ) ) . ) )
(ROOT (S (NP (NNS Amphibians)) (VP (VBP are) (NP (NP (DT the) (JJ first) (JJ true) (NNS tetrapods)) (, ,) (CC or) (NP (NP (NNS vertebrates)) (PP (IN with) (NP (CD four) (NNS limbs)))))) (. .)))
Amphibians are the first true tetrapods,  or vertebrates with four limbs.
(ROOT (S (NP (NP (NNS Amphibians)) (PRN (-LRB- -LRB-) (CC or) (ADJP (JJ tetrapods)) (-RRB- -RRB-))) (VP (VBD were) (NP (NP (DT the) (JJ first)) (PP (IN with) (NP (CD four) (NNS limbs))))) (. .)))