( They ( ( have ( ( ( a ( thick layer ) ) ( of skin ) ) ( that ( keeps ( them floating ) ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBP have) (NP (NP (DT a) (JJ thick) (NN layer)) (PP (IN of) (NP (NN skin))) (SBAR (WHNP (WDT that)) (S (VP (VBZ keeps) (S (NP (PRP them)) (VP (VBG floating)))))))) (. .)))
They have a thick layer of skin that keeps them floating.
(ROOT (S (NP (NP (DT The) (JJ thick) (NN skin)) (, ,) (VP (VBN found) (ADVP (RB only)) (PP (IN on) (NP (NP (NP (DT the) (NNS palms)) (PP (IN of) (NP (DT the) (NNS hands)))) (CC and) (NP (NP (DT the) (NNS soles)) (PP (IN of) (NP (DT the) (NNS feet))))))) (, ,)) (VP (VBZ has) (NP (DT an) (JJ extra) (NN layer))) (. .)))