A new family of Eocene zygodactyl birds

Abstract

The Pseudasturidae, a new family of small Lower to Middle Eocene zygodactyl birds is described. In the Middle Eocene of Grube Messel, near Darmstadt (Hessen, Germany), this taxon is represented by at least two species (Pseudastur macrocephalus n. g., n. sp. and an unnamed species). A third (unnamed) species is tentatively referred to the Pseudasturidae. The Lower Eocene species 'Primobucco' olsoni Feduccia and Martin 1976 from the Green River Formation (Wyoming) is also included in this family. Since it has not been possible to find derived characters which convincingly link the Pseudasturidae to any of the known Recent or fossil orders, the family is classified incertae sedis in this study. Most characteristic for Pseudastur macrocephalus is the presence of large processus supraorbitales, which closely resemble the corresponding structures found in falconiform birds. The fact that the skull of Messelastur gratulator Peters 1994 is difficult to distinguish from that of one of the unnamed species presented here raises the question, whether Messelastur is correctly assigned to the Falconiformes or if this genus represents another taxon of the Pseudasturidae.