( ( ( ( ( ( ( The ancestor ) ( of tetrapods ) ) ( evolved ( four limbs ) ) ) , ) and ) ( ( its descendents ) ( have ( inherited ( that ( ( ( feature-so ( the presence ) ) ( of ( four limbs ) ) ) ( is ( a homology ) ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (NP (DT The) (NN ancestor)) (PP (IN of) (NP (NNS tetrapods)))) (VP (VBD evolved) (NP (CD four) (NNS limbs)))) (, ,) (CC and) (S (NP (PRP$ its) (NNS descendents)) (VP (VBP have) (VP (VBN inherited) (SBAR (IN that) (S (NP (NP (JJ feature-so) (DT the) (NN presence)) (PP (IN of) (NP (CD four) (NNS limbs)))) (VP (VBZ is) (NP (DT a) (NN homology)))))))) (. .)))
The ancestor of tetrapods evolved four limbs, and its descendents have inherited that feature-so the presence of four limbs is a homology.
(ROOT (S (NP (NNS Caecillians)) (VP (VBD evolved) (PP (IN from) (NP (JJ tetrapod) (NNS ancestors)))) (. .)))