Wikipedia
Lithornithidae is an extinct, possibly paraphyletic (but see below) clade 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.
Lithornithids had long, slender, bills for probing. They closely resembled modern tinamous. They possessed a rhynchokinetic skull with relatively unfused cranial bones, a weakly fused pygostyle and a splenial. The unguals were more curved than in tinamous and probably allowed better perching in trees.
The order Lithornithiformes was erected by Dr. Peter Houde in 1988. Three genera are included; Lithornis, Paracathartes, and Pseudocrypturus. There are eight named species. Promusophaga ( Harrisson & Walker, 1977) originally considered a stem- turaco, is considered synonimous with Lithornis vulturinus. Fissuravis may also belong to the clade, and several unnamed remains are known.