( ( Relative ( to ( ( the amniotes ) ( -LRB- ( ( ( reptiles , ) ( ( ( ( birds and ) mammals ) , ) ( ( all ( of which ) ) ( ( produce embryos ) ( with ( ( ( an amnion ) and ) ( other ( embryonic membranes ) ) ) ) ) ) ) ) -RRB- ) ) ) ) ) ( , ( ( the amphibians ) ( ( may ( ( look ( primitive ( , ( if only ) ) ) ) ( because ( ( many species ) ( develop ( through ( a ( fish-like tadpole ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (S (ADJP (JJ Relative) (PP (TO to) (NP (NP (DT the) (NNS amniotes)) (PRN (-LRB- -LRB-) (NP (NP (NNS reptiles)) (, ,) (NP (NP (NNS birds) (CC and) (NNS mammals)) (, ,) (SBAR (WHNP (DT all) (WHPP (IN of) (WHNP (WDT which)))) (S (VP (VBP produce) (NP (NNS embryos)) (PP (IN with) (NP (NP (DT an) (NN amnion)) (CC and) (NP (JJ other) (JJ embryonic) (NNS membranes))))))))) (-RRB- -RRB-)))))) (, ,) (NP (DT the) (NNS amphibians)) (VP (MD may) (VP (VB look) (ADJP (JJ primitive) (, ,) (IN if) (JJ only)) (SBAR (IN because) (S (NP (JJ many) (NNS species)) (VP (VBP develop) (PP (IN through) (NP (DT a) (JJ fish-like) (NN tadpole)))))))) (. .)))
Relative to the amniotes (reptiles, birds and mammals, all of which     produce embryos with an amnion and other embryonic membranes), the amphibians     may look primitive, if only because many species develop through a fish-like     tadpole.
(ROOT (S (SBAR (IN Because) (S (NP (PRP$ their) (NNS embryos)) (VP (VBP are) (VP (VBN surrounded) (PP (IN by) (NP (DT a) (JJ thin) (NN membrane))))))) (, ,) (NP (NNS reptiles)) (VP (VBP are) (VP (VBN considered) (NP (NNS amniotes)))) (. .)))