Osteodontornis is an extinct genus of pelecaniform bird. It contains a single described species, O. orri ("Orr's Bony-toothed Bird"), which was the first of the Pelagornithidae or "pseudo-tooth birds" to become known to science. The arrangement of serrations of the bill - one small "tooth", sometimes flanked by small points, between each 2 larger ones - is characteristic for this genus. This species is well documented (although usually by much fragmented remains due to the thin and tender bones it had) from various locations, between Early Oligocene and Pliocene in age, in Europe, Western North America and Japan. Most importantly, it was found in Early and Middle Miocene sites on both sides of the North Pacific. It is not certain whether all Osteodontornis remains belong to a single species; size differences suggest that some evolution took place during the considerable timespan in which the genus existed. Thus, some fossils are referred to Osteodontornis only, without further assigning them to this species.
With a wingspan of 5,5-6 m (c.18-20 ft) and a height of 1,20 m (4 ft) when on the ground (Olson, 1985), Osteodontornis orri was the second-largest flying bird known, surpassed only by Argentavis. It had a robust, but extremely light-boned body, procellariiform-like legs and a long beak with teeth-like serrations (not unlike the saw-billed ducks) that ended in a hooked tip. This beak was so heavy the creature probably held it between its shoulders while in flight, just like modern pelicans do.
Osteodontornis wings were long and narrow. Due to its size, the creature is presumed to have built its nest on high plateaus where it could easily take flight. It was a seabird that apparently lived mainly off squid; the "teeth" were less saw-like than in the fish-eating saw-billed ducks, pointing straight downwards instead. This arrangement would have helped to hold on to such soft-bodied prey. In general lifestyle, it was probably most similar to the albatrosses, tropicbirds and frigatebirds of today, with long slender winds adapted for soaring vast distances over the open seas.
The species was named after then-recently deceased naturalist Ellison Orr.