I've seen a recent study based on osteology "behavior and ecology" which seems to agree with molecular studies on the paraphyletic and basal nature of terrestrial cuckoos, that arboreal cuckoos are derived and monophyletic, and that brood parasitism evolved twice in Cuculiformes.    From Wordnik.com.  [Goodbye, my giant predatory, cursorial, flightless hoatzin] Reference

Phylogenetic analysis of Cuculiformes (Aves) based on osteology, behavior and ecology: systematics and evolutionary implications.    From Wordnik.com.  [Goodbye, my giant predatory, cursorial, flightless hoatzin] Reference

Cuculiformes.    From Wordnik.com.  [Bird lists] Reference