( ( ( These similarities ) ( in ( bone structure ) ) ) ( ( indicate ( that ( ( these ( four mammals ) ) ( may ( have ( evolved ( from ( a ( common ancestor ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT These) (NNS similarities)) (PP (IN in) (NP (NN bone) (NN structure)))) (VP (VBP indicate) (SBAR (IN that) (S (NP (DT these) (CD four) (NNS mammals)) (VP (MD may) (VP (VB have) (VP (VBN evolved) (PP (IN from) (NP (DT a) (JJ common) (NN ancestor))))))))) (. .)))
These similarities in bone structure indicate that these four mammals may have evolved from a common ancestor.
(ROOT (S (NP (NP (DT The) (NN conclusion)) (SBAR (IN that) (S (NP (CD two) (NN animal) (NNS species)) (VP (VBD evolved) (PP (IN from) (NP (DT a) (JJ common) (NN ancestor))) (PP (IN in) (NP (JJ recent) (JJ geological) (NN history))))))) (VP (VBZ is) (ADVP (RBS best)) (VP (VBN supported) (PP (IN by) (NP (DT the) (NN observation))) (SBAR (IN that) (S (NP (DT the) (NNS species)) (VP (VBP have) (NP (JJ similar) (NN bone) (NN structure))))))) (. .)))
The conclusion that two animal species evolved from a common ancestor in recent geological history is best supported by the observation that the species have similar bone structure.