( ( ( ( ( Crown-group tetrapods ) ( are ( descendants ( of ( ( the ( most ( recent ( common ancestor ) ) ) ) ( of ( all ( living tetrapods ) ) ) ) ) ) ) ) and ) ( ( stem tetrapods ) ( are ( forms ( that ( are ( outside ( the ( crown group ) ) ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (JJ Crown-group) (NNS tetrapods)) (VP (VBP are) (NP (NP (NNS descendants)) (PP (IN of) (NP (NP (DT the) (RBS most) (JJ recent) (JJ common) (NN ancestor)) (PP (IN of) (NP (DT all) (VBG living) (NNS tetrapods)))))))) (CC and) (S (NP (NN stem) (NNS tetrapods)) (VP (VBP are) (NP (NP (NNS forms)) (SBAR (WHNP (WDT that)) (S (VP (VBP are) (PP (IN outside) (NP (DT the) (NN crown) (NN group))))))))) (. .)))
Crown-group tetrapods are descendants of the most recent common ancestor of all living tetrapods and stem tetrapods are forms that are outside the crown group.
(ROOT (S (NP (NNS Caecillians)) (VP (VBD evolved) (PP (IN from) (NP (JJ tetrapod) (NNS ancestors)))) (. .)))