( It ( ( ( was formerly ) ( thought ( that ( ( vertebrates ( with ( ( cartilage skeletons ) ( -LRB- ( ( ( cyclostomes and ) ( sharklike fishes ) ) -RRB- ) ) ) ) ) ( were ( descended ( from ( ( early vertebrates ) ( that ( ( ( had not ) yet ) ( developed bone ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBD was) (ADVP (RB formerly)) (VP (VBN thought) (SBAR (IN that) (S (NP (NP (NNS vertebrates)) (PP (IN with) (NP (NP (NN cartilage) (NNS skeletons)) (PRN (-LRB- -LRB-) (NP (NP (NNS cyclostomes)) (CC and) (NP (JJ sharklike) (NNS fishes))) (-RRB- -RRB-))))) (VP (VBD were) (VP (VBN descended) (PP (IN from) (NP (NP (JJ early) (NNS vertebrates)) (SBAR (WHNP (WDT that)) (S (VP (VBD had) (RB not) (ADVP (RB yet)) (VP (VBN developed) (NP (NN bone)))))))))))))) (. .)))
It was formerly thought that vertebrates with cartilage skeletons (cyclostomes and sharklike fishes) were descended from early vertebrates that had not yet developed bone.
(ROOT (S (ADVP (RB Early) (PP (IN in) (NP (NP (DT the) (NN development)) (PP (IN of) (NP (DT a) (JJ human) (NN fetus)))))) (, ,) (NP (DT the) (NN skeleton)) (VP (VBZ is) (VP (VBN made) (ADVP (RB entirely)) (PP (IN of) (NP (NN cartilage))))) (. .)))