( ( ( ( ( ( ( Sharks , ) and ) rays ) ( ( have skeletons ) ( ( composed entirely ) ( of cartilage ) ) ) ) ; ) ( ( other vertebrates ) ( ( have ( ( an ( embryonic ( cartilage skeleton ) ) ) ( progressively ( replaced ( by bone ) ) ) ) ) ( as ( they ( ( mature and ) develop ) ) ) ) ) ) . )
(ROOT (S (S (NP (NP (NNS Sharks)) (, ,) (CC and) (NP (NNS rays))) (VP (VBP have) (ADVP (RB skeletons)) (VP (VBN composed) (ADVP (RB entirely)) (PP (IN of) (NP (NN cartilage)))))) (: ;) (S (NP (JJ other) (NNS vertebrates)) (VP (VBP have) (NP (NP (DT an) (JJ embryonic) (NN cartilage) (NN skeleton)) (VP (ADVP (RB progressively)) (VBN replaced) (PP (IN by) (NP (NN bone))))) (SBAR (IN as) (S (NP (PRP they)) (VP (VBP mature) (CC and) (VBP develop)))))) (. .)))
Sharks, and rays have skeletons composed entirely of cartilage; other vertebrates have an embryonic cartilage skeleton progressively replaced by bone as they mature and develop.
(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))))) (. .)))