( ( ( ( ( ( Mammals and ) birds ) , ) ( which ( both ( descended ( from ( reptile-like ancestors ) ) ) ) ) ) , ) ( ( ( ( ( evolved endothermy ) , ) or ) ( ( the ability ) ( to ( ( regulate ( body temperature ) ) ( from ( the inside ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NNS Mammals) (CC and) (NNS birds)) (, ,) (SBAR (WHNP (WDT which)) (S (DT both) (VP (VBD descended) (PP (IN from) (NP (JJ reptile-like) (NNS ancestors)))))) (, ,)) (VP (VP (VBD evolved) (ADVP (RB endothermy))) (, ,) (CC or) (VP (NP (DT the) (NN ability)) (S (VP (TO to) (VP (VB regulate) (NP (NN body) (NN temperature)) (PP (IN from) (NP (DT the) (NN inside)))))))) (. .)))
Mammals and birds, which both descended  from reptile-like ancestors, evolved endothermy, or the ability to regulate body temperature from the  inside.
(ROOT (S (NP (NNP Birds)) (VP (VBD evolved) (PP (IN from) (NP (JJ reptile) (NNS ancestors)))) (. .)))