Stem Parrots (Aves, Halcyornithidae) from the Green River Formation and a Combined Phylogeny of Pan-Psittaciformes Ksepka, Daniel T. ; Clarke, Julia A. ; Grande, Lance Abstract Publication: Journal of Paleontology Pub Date: September 2011 DOI: 10.1666/10-108.1 Bibcode: 2011JPal...85..835K