Limnofregata is an extinct genus of primitive frigatebird. The two known species were described after fossils from the Early Eocene Green River Formation of Wyoming. A number of good complete and partial skeletons, some with feather impressions, are known of the type species, Limnofregata azygosternon, and L. hasegawai is known from two skulls and most of one torso.
Archaeotrogonidae is a prehistoric bird family known from the Eocene and Oligocene of Europe. They are members of Strisores, and are thought to be closely related to nightjars.
Lithornis is a genus of extinct paleognathous birds. Although Lithornis was able to fly well, their closest relatives are the extant tinamous and ratites.
Eurofluvioviridavis is a genus of extinct birds from the Middle Eocene Messel Pit, Germany. It contains a single species, Eurofluvioviridavis robustipes. It is related to Avolatavis and Vastanavis, other members of the family Vastanavidae.
Eostrix is a genus of extinct primitive owls in the family Protostrigidae, along with Oligostrix and Minerva. These owls date from the early Eocene of the United States, Europe, and Mongolia. They have been described based on fossil remains. The genus was created by Pierce Brodkorb in 1971 to place a fossil species known until that time as Protostrix mimica.
Avolatavis is an extinct genus of stem-parrot (pan-psittaciform) or a member of the stem group of Psittacopasseres, known from the early Eocene Fossil Butte Member of the Green River Formation of Wyoming, United States, and from the London Clay of Walton-on-the-Naze. It was first named by Daniel T. Ksepka and Julia A. Clarke in 2012 and the type species is Avolatavis tenens. Gerald Mayr and Andrew C. Kitchener described the second species, A. europaeus, in 2023. Mayr and Kitchener assigned Avolatavis to the family Vastanavidae, which might be early diverging stem group presentatives of Pan-Psittaciformes or stem group representatives of Psittacopasseres.
The Willwood Formation is a sedimentary sequence deposited during the late Paleocene to early Eocene, or Clarkforkian, Wasatchian and Bridgerian in the NALMA classification.
Gerald Mayr is a German palaeontologist who is Curator of Ornithology at the Senckenberg Research Institute in Frankfurt am Main, Hesse. He has published extensively on fossil birds, especially the Paleogene avifauna of Europe. He is an expert on the Eocene fauna of the Messel pit.
Messelasturidae is an extinct family of birds known from the Eocene of North America and Europe. Their morphology is a mosaic that in some aspects are very similar to modern hawks and falcons, but in others are more similar to parrots. Initially interpreted as stem-owls, more recent studies have suggested a closer relationship to parrots and passerines. Their ecology is enigmatic.
Vastanavidae is an extinct family of birds related to parrots and passerine birds. They are known from fossils from Eocene sites in India, Europe, and North America. The vastanavids resemble parrots and the extinct parrot relative Quercypsitta in their morphology, including the partially zygodactyl foot, in which two toes could face opposite the other two.
Halcyornithidae is an extinct family of telluravian birds thought to be related to the Psittaciformes (parrots), Passeriformes (songbirds), and to the extinct Messelasturidae. Halcyornithids have been found in various Eocene formations in Europe and North America. Widespread and diverse in the Early Eocene of North America and Europe, halcyornithids are not found in locales later than the Middle Eocene. Halcyornithids were small, arboreal birds with zygodactyl feet, with two toes facing forwards and two facing back, a trait shared with other tree-dwelling families of Eocene birds like the Zygodactylidae and the messelasturids. The skull of halcyornithids features a ridge of bone above the eye called the supraorbital process, similar to birds of prey. The relationships of the halcyornithids to other birds remain uncertain. Halcyornithids have been proposed as relatives to owls and as a lineage closer to parrots than to songbirds. Most recently, halcyornithids have been identified as the sister group of the clade including parrots and songbirds. It is also possible that Halcyornithidae is paraphyletic with respect to the Messelasturidae.
Ueekenkcoracias is an extinct genus of bird from the Huitrera Formation of Patagonia. Initially assigned to Coracii, similarities have instead been noted with Palaeopsittacus, and it may instead be more closely related to Strisores, the clade including hummingbirds, nightjars, and swifts. One species of Ueekenkcoracias, U. tambussiae, has been named.
Morsoravis is an extinct genus of neoavian bird from the Early Eocene Fur Formation of Denmark. It contains a single named species, Morsoravis sedilis. Fossils of Morsoravis have also been found in the Green River Formation of Wyoming and possibly the Nanjemoy Formation of Virginia.
Ypresiglaux is an extinct genus of strigiform bird from the Early Eocene London Clay Formation of Essex, United Kingdom and Nanjemoy Formation of Virginia, United States. The genus contains two species: Y. michaeldanielsi, known from a partial skeleton, and Y. gulottai, known from a distal tarsometatarsus.
Minutornis is an extinct genus of parapasserine bird from the Early Eocene London Clay Formation of Essex, United Kingdom. The genus contains a single species, M. primoscenoides, known from a fragmentary skeleton.
Pulchrapollia is an extinct genus of halcyornithid bird from the Early Eocene London Clay of Walton-on-the-Naze, United Kingdom and the Nanjemoy Formation of Virginia, United States. The genus contains three species, Pulchrapollia gracilis, Pulchrapollia tenuipes and Pulchrapollia eximia.
Eofringillirostrum is an extinct species of bird known from the Early Eocene Green River Formation of the Western United States and from the Messel Pit in Germany. The genus contains two species, Eofringillirostrum boudreauxi and Eofringillirostrum parvulum. They are the earliest known fossil birds to have a finch-like beak.
Pristeanis is an extinct genus of piciform bird known from the Early Eocene. The genus contains three species. Pristineanis minor and Pristineanis major are known from the London Clay in the United Kingdom, while Pristeanis kistneri is known from the Green River Formation in the United States.
The Green River Formation is a geological formation located in the Intermountain West of the United States, in the states of Colorado, Utah, and Wyoming. It comprises sediments deposited during the Early Eocene in a series of large freshwater lakes: Lake Gosiute, Lake Uinta, and Fossil Lake. It preserves a high diversity of freshwater fish, birds, reptiles, and mammals, with some sections of the formation qualifying as Konservat-Lagerstätten due to their extremely well-preserved fossils.
Archaeodromus anglicus is a species of prehistoric bird in the family Archaeotrogonidae, found in the Early Ypresian of the London Clay formation. It is the only species in the monotypic genus Archaeodromus. Both species and genus were described in 2021 by Gerald Mayr.
