Lithornithidae

Lithornithidae is an extinct, possibly paraphyletic (but see below) 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.

Pseudocrypturus is a genus of extinct paleognathous bird. Three species are known and the type species is 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.

Lithornis is a genus of extinct paleognathous birds. Although Lithornis was able to fly well, their closest relatives are the extant tinamous (which are poor flyers) and ratites (which are flightless birds).