( ( If true ) ( , ( they ( ( would ( ( be ( ( compelling evidence ) ( of ( the ( widely ( accepted theory ) ) ) ) ) ) ( that ( ( modern-day birds ) ( ( descended directly ) ( from dinosaurs ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN If) (FRAG (ADJP (JJ true)))) (, ,) (NP (PRP they)) (VP (MD would) (VP (VB be) (NP (NP (JJ compelling) (NN evidence)) (PP (IN of) (NP (DT the) (RB widely) (VBN accepted) (NN theory)))) (SBAR (IN that) (S (NP (JJ modern-day) (NNS birds)) (VP (VBD descended) (ADVP (RB directly)) (PP (IN from) (NP (NNS dinosaurs)))))))) (. .)))
If true, they would be compelling evidence of the widely accepted theory that modern-day birds descended directly from dinosaurs.
(ROOT (S (NP (NN Evidence)) (VP (VBZ allows) (S (NP (NNS theories)) (VP (TO to) (VP (VB be) (VP (ADVP (RB widely)) (VBN accepted)))))) (. .)))