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''Osteodontornis'' is an extinct seabird genus. It contains a single named species, ''Osteodontornis orri'' (Orr's Bony-toothed Bird, in literal translation of its scientific name), which was described quite exactly one century after the first species of the Pelagornithidae (''Pelagornis miocaenus'') was. ''O. orri'' was named after then-recently deceased naturalist Ellison Orr.〔Howard (1957), Olson (1985: p.198)〕 The bony-toothed or pseudotooth birds were initially believed to be related to albatrosses in the Procellariiformes, but actually they seem to be rather close relatives of either pelicans and storks, or of waterfowl, and are here placed in the order Odontopterygiformes to account for this uncertainty. Also, their internal taxonomy is not well-resolved. An earlier-described pseudotooth bird, ''Cyphornis magnus'' from Vancouver Island (Canada), was believed to be of Eocene age but is nowadays assumed to have lived in the Early Miocene, not too long before the Clarendonian (Middle/Late Miocene) ''O. orri''. It may be that ''Osteodontornis'' is a junior synonym of ''Cyphornis''.〔Bourdon (2005), Olson (1985: pp.198-199), Mayr (2009: p.59)〕 ==Description== With a wingspan of and a height of when on the ground, ''Osteodontornis orri'' and similar giant pseudotooth birds〔E.g. the Paleogene ''Dasornis emuinus'' and ''Gigantornis eaglesomei'', or the Atlantic contemporary of ''Osteodontornis'', ''Pelagornis miocaenus''〕 were the second-largest flying birds known, surpassed only by the teratorn ''Argentavis magnificens''. The head, from neck to bill-tip, measured about , and the eyesockets were about wide. The humerus, though about as long as a human's, was only about wide at the shoulder end. The skull's quadrate bone measured almost at its widest and was nearly high.〔Howard (1957), Olson (1985: pp.199-200), Ono (1989), Mayr (2008), Mayr ''et al.'' (2008)〕 Like its relatives, ''O. orri'' had a stout but extremely light-boned body, feet that were presumably webbed as in its aquatic relatives, and long and probably very narrow wings resembling those of an albatross. Its beak made up about three-quarters of the head's length and had bony tooth-like serrations that were hollow or maybe filled with cancellous bone. The beak was so heavy the creature probably held it between its shoulders while in flight, just like modern pelicans do. The arrangement of its bony serrations is characteristic for this genus: one small "tooth", flanked by small points or even smaller "teeth", is placed between each pair of large ones. However, the "tooth" pattern of pseudotooth birds changed along the length of the beak, and is not considered a very reliable way to distinguish genera.〔Hopson (1964), Olson (1985: pp.199-200), Matsuoka ''et al.'' (1998), Palmer (1999: p.180), Rincón R. & Stucchi (2003)〕 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. Due to its size, the bird is presumed to have been an excellently adapted dynamic soarer. It probably built its nest on high plateaus or similar places, where it could easily take flight by simply walking into the wind with wings spread. 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. Lightly built as it was, ''O. orri'' was probably not a good diver and may have found it impossible to dive at all.〔Olson (1985: pp.199-200), Palmer (1999: p.180)〕 ''Osteodontornis'' is one of the pseudotooth birds of which rather comprehensive remains are known, but the lack of good fossils of most other Odontopterygiformes allows for few direct comparisons between genera. 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〔Specimen MHN-UABCS Te5/6–517, from Middle Eocene strata of the Tepetate Formation near El Cien (Baja California Sur, Mexico): González-Barba ''et al.'' (2002)〕 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. Its quadrate bone differed from that of ''Odontopteryx toliapica'' in a more narrowly grooved dorsal head, and a larger and less forward-pointing orbital process. The forward center of the ventral articulation ridge extends upwards and forward, and the pterygoid process is conspicuously expanded to the upper center in ''Osteodontornis''. The socket for the quadratojugal has an intermediate position and the lateral ridge of the slender main shaft is straight and fairly thin. The quadrate of the mysterious ''Pseudodontornis longirostris'' skull (which some consider to belong in ''Pelagornis'') is not very well preserved; it agees with ''Odontopteryx'' in a broad main shaft and with ''Osteodontornis'' in the straight main shaft ridge and its upward-directed ventral articulation ridge's forward center. Otherwise, it differs from both.〔Olson (1985: pp.195,198), Ono (1989), González-Barba ''et al.'' (2002)〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Osteodontornis」の詳細全文を読む スポンサード リンク
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