Lithornithidae is an extinct, possibly paraphyleticclade of early paleognathbirds. They are known from fossils dating to the Upper Paleocene through the MiddleEocene 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 rhynchokineticskull 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. Initially, only three genera and eight named species were included. Promusophaga originally considered a stem-turaco, is considered synonymous with Lithornis vulturinus. Fissuravis may also belong to the clade, and several unnamed remains are known.
Several studies have shown conflicting status on the monophyly of the group. Some studies recover them as a paraphyletic assemblage leading to modern paleognaths, but more recent examinations group them in a single, natural groupbasal to the rest of Palaeognathae. Of issue is Paracathartes, which differs radically from other lithornithids and has been suggested to more closely related to extant paleognaths, though it is recently recovered as a derived lithornithid. Lithornis itself may be paraphyletic in relation to Paracathartes and Pseudocrypturus.
Paleobiology
In a study about ratite endocasts, Lithornis ranks among the taxa with well developed olfactory lobes. This is consistent with a nocturnal, forest-dwelling lifestyle, though as much all volant birds it retains large optical lobes. Unlike modern tinamous, at least Lithornis has toe claws and reversed halluxes that allow for efficient perching. Several egg fossils have been attributed to lithornithid birds. Both Lithornis and Paracathartes have entirenests assigned to them. Their eggshells are, perhaps unsurprisingly, noted as being "ratite-like". Studies on lithornithid feathers shows that some species had gloss similar to that of cassowaries.
