[5] In general lifestyle, it was probably most similar to the albatrosses, tropicbirds and frigatebirds of today, with long slender wings adapted for soaring vast distances over the open seas.

It was a seabird that apparently lived mainly off squid and other soft-bodied prey; the "teeth" were less saw-like than the horny serrations on the beak of the fish-eating saw-billed ducks (Merginae), pointing straight downwards instead and in the fossils often very abraded or broken.

The downward-pointing "teeth" were ideal for digging into and holding slippery, soft-skinned pelagic animals such as cephalopods that were probably snatched out of the water in flight or while swimming.

Still, the distal humerus of the present genus (e.g. the Barstovian specimen LACM 50660 from Kern County, California) can be compared to that of a smaller and older fossil[7] tentatively assigned to Odontopteryx.

Osteodontornis has a wider and deeper notch between the external condyle and the ectepicondylar prominence, with the pit between these farther from the bone's end, than did the smallish Paleogene species.

[9] The type specimen of O. orri, SBMNH 309, is a rather comprehensive fossil preserved mostly as imprint, with some bone pieces and even feather impressions in addition; it was found in Clarendonian (Late Miocene) shale of California (USA).

The former, specimen MBLUZ-P-5093 from Cueva del Zumbador in Falcón State, is a premaxilla tip of immense dimensions; its bearer might have exceeded a wingspan of 7 metres (23 ft) in life.

They are the oldest known remains of large North Pacific pseudotooth birds, but if the enigmatic Cyphornis magnus from the same region dates back to the Paleogene they may well be assignable to that taxon, whatever their systematic affiliations might be beyond that.

Generally, recent authors have tended to place large Neogene pseudotooth bird fossils from the Atlantic in Pelagornis, and those from the North Pacific in Osteodontornis.

Its jugal arch is indeed short and very stout behind the orbital process of the prefrontal bone, like in Osteodontornis but apparently unlike in the type species of its supposed genus, P. longirostris.

A larger proximal (initially misidentified as distal) humerus piece (CMNZ AV 24,960), probably from the Waiauan (Middle/Late Miocene) and found near the Waipara River mouth, is little if any distinct from O. orri in shape and size; it has a flange at the side and is less straight, but whether these features are natural or due to the damaged state of the specimens is unclear.

A distal left humerus end and some wing bone fragments from the Late Oligocene Yamaga Formation of Kitakyūshū (Japan) might be the oldest remains of an Osteodontornis, but their assignment to the present genus is just as uncertain as in the case of the New Zealand fossil.