( ( ( A ( third group ) ) ( of ( ( ( tetrapods , ) ( the anthracosaurs ) ) , ) ) ) ( ( include ( ( the ancestors ) ( of amniotes ) ) ) . ) )
(ROOT (S (NP (NP (DT A) (JJ third) (NN group)) (PP (IN of) (NP (NP (NNS tetrapods)) (, ,) (NP (DT the) (NNS anthracosaurs)) (, ,)))) (VP (VBP include) (NP (NP (DT the) (NNS ancestors)) (PP (IN of) (NP (NNS amniotes))))) (. .)))
A third group of tetrapods, the anthracosaurs , include the ancestors of amniotes .
(ROOT (S (NP (NNS Caecillians)) (VP (VBD evolved) (PP (IN from) (NP (JJ tetrapod) (NNS ancestors)))) (. .)))