A new zygodactylid species indicates the persistence of stem passerines into the early Oligocene in North America

Background The lake deposits of the informal Ruby Paper Shale unit, part of the Renova Formation of Montana, have yielded abundant plant fossils that document Late Eocene – Early Oligocene global cooling in western North America. A nearly complete small bird with feather impressions was recovered from this unit in in 1959, but has only been informally mentioned.