Ratites are a polyphyletic group consisting of all birds within the infraclass Palaeognathae that lack keels and cannot fly. They are mostly large, long-necked, and long-legged, the exception being the kiwi, which is also the only nocturnal extant ratite.
Struthionidae is a family of flightless birds, containing the extant ostriches and their extinct relatives. The two extant species of ostrich are the common ostrich and Somali ostrich, both in the genus Struthio, which also contains several species known from Holocene fossils such as the Asian ostrich. The common ostrich is the more widespread of the two living species, and is the largest living bird species. The extinct genus Pachystruthio from the Late Pliocene-Early Pleistocene of Eurasia is one of the largest birds ever.
Rheidae is a family of flightless ratite birds which first appeared in the Paleocene. It is today represented by the sole living genus Rhea, but also contains several extinct genera.
The mousebirds are birds in the order Coliiformes. They are the sister group to the clade Cavitaves, which includes the Leptosomiformes, Trogoniformes (trogons), Bucerotiformes, Piciformes and Coraciformes. This group is now confined to sub-Saharan Africa, and it is the only bird order confined entirely to that continent, with the possible exception of turacos which are considered by some as the distinct order Musophagiformes, and the cuckoo roller, which is the only member of the order Leptosomiformes, and which is found in Madagascar but not mainland Africa. Mousebirds had a wider range in the Paleogene, with a widespread distribution in Europe and North America during the Paleocene.
Palaeognathae is an infraclass of birds, called paleognaths or palaeognaths, within the class Aves of the clade Archosauria. It is one of the two extant infraclasses of birds, the other being Neognathae, both of which form Neornithes. Palaeognathae contains five extant orders consisting of four flightless lineages, termed ratites, and one flying lineage, the Neotropic tinamous. There are 47 species of tinamous, five of kiwis (Apteryx), three of cassowaries (Casuarius), one of emus (Dromaius), two of rheas (Rhea) and two of ostriches (Struthio). Recent research has indicated that paleognaths are monophyletic but the traditional taxonomic split between flightless and flighted forms is incorrect; tinamous are within the ratite radiation, meaning flightlessness arose independently multiple times via parallel evolution.
Presbyornis is an extinct genus of presbyornithid bird from North America during the Paleogene period, between the Late Paleocene and Early Eocene.
Palaeotis is a genus of paleognath birds from the middle Eocene epoch of central Europe. One species is known, Palaeotis weigelti. The holotype specimen is a fossil tarsometatarsus and phalanx. Lambrect (1928) described it as an extinct bustard, and gave it its consequent name. After a suggestion by Storrs L. Olson, a review of the type specimen and the referral of several other fossils by Houde and Haubold (1987) concluded that Palaeotis is a palaeognath and assigned it to the same order as ostriches; the Struthioniformes. In 2021, it was considered a member of the family Paleotididae alongside Galligeranoides from the Early Eocene of France, which were found to be basal members of the Struthioniformes.
Limenavis is a genus of ornithuran dinosaurs from the Late Cretaceous. It lived about 70 million years ago, around the Campanian-Maastrichtian boundary. Known from several broken bones, the remains of the only known species Limenavis patagonica were found in rocks of the "lower member" of the Allen Formation at Salitral Moreno, 20 km south of General Roca, Río Negro (Argentina). It is one of the closest relatives, in the fossil record, of the modern birds.
The Fur Formation is a marine geological formation of Ypresian age which crops out in the Limfjord region of northern Denmark from Silstrup via Mors and Fur to Ertebølle, and can be seen in many cliffs and quarries in the area. The Diatomite Cliffs is on the Danish list of tentative candidates for World Heritage and may become a World Heritage site. Fossils found in the Fur Formation are primarily housed at the Fossil and Mo-clay Museum on Mors Island, the Fur Museum on Fur Island, and the Natural History Museum of Denmark in Copenhagen.
Diogenornis is an extinct genus of ratites, that lived from the Middle Paleocene to the Early Eocene. It was described in 1983 by Brazilian scientist Herculano Marcos Ferraz de Alvarenga based on fossils found in the Itaboraí Formation in southeastern Brazil. The type species is D. fragilis. It grew to about two thirds the size of the modern greater rhea, at about 90 centimetres (3.0 ft) of height.
Odontopteryx is a genus of the extinct pseudotooth birds or pelagornithids. These were probably rather close relatives of either pelicans and storks, or of waterfowl, and are here placed in the order Odontopterygiformes to account for this uncertainty.
Lithornithidae is an extinct, possibly paraphyletic group of early paleognath birds. They are known from fossils dating to the Upper Paleocene through the Middle Eocene of North America and Europe, with possible Late Cretaceous representatives. All are extinct today; the youngest specimen is the currently unnamed SGPIMH MEV1 specimen from the mid-Eocene Messel Pit site.
Paracathartes is a genus of extinct bird from the Wasachtian horizon of lower Eocene Wyoming. One species, Paracathartes howardae has been described.
Pseudocrypturus is a genus of extinct paleognathous bird. One species is known, Pseudocrypturus cercanaxius. It is a relative of such modern birds as ostriches. It lived in the early Eocene. The holotype fossil is in the collection of the Smithsonian's National Museum of Natural History. It has catalog number USNM 336103. It was collected from the Fossil Butte Member, Green River Formation, Lincoln County, Wyoming.
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.
Calciavis is an extinct genus of bird from the Eocene of Wyoming. It is a lithornithid, a member of a lineage of flying palaeognaths, distantly related to modern ratites. Like many other fossils from the Green River Formation, its are exceptionally well preserved, bearing impressions of skin and feathers. Some researchers consider this taxon as a species of Lithornis.
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.
Geranoididae is a clade of extinct birds from the early to late Eocene and possibly early Oligocene of North America and Europe. These were mid-sized, long-legged flightless birds. Recent research shows that these birds may actually be palaeognaths related to ostriches.
