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''Pseudodontornis'' is a rather disputed genus of the prehistoric pseudotooth birds. The pseudotooth birds or pelagornithids were probably rather close relatives of either pelicans and storks, or of waterfowl, and are here placed in the order Odontopterygiformes to account for this uncertainty. Up to five species are commonly recognized in this genus.〔Olson (1985: pp.198–199), Bourdon (2005), Mlíkovský (2002: p.82), Mayr (2009: pp.56,59)〕 But actually the genus ''Pseudodontornis'' is barely more than a ''nomen nudum''. And though it served as the namesake for a popular alternate common name of the pseudotooth birds – "pseudodontorns" or "pseudodontornids" – that was extensively used in the 20th century, current authors prefer "pelagornithids" because this is less fraught with taxonomic dispute. ''Pelagornis'', the type genus of the family Pelagornithidae, was long unrecognized as a pseudotooth bird as it was known mainly from arm bones. Thus, though the Pelagornithidae were long recognized as very distinct, they were allied with the cormorant and gannet in suborder Sulae (or superfamily Sulides in suborder Pelecanae) before it was recognized that they are actually pseudotooth birds. The presumed family "Pelagornithidae", deemed invalid nowadays, had been recognized as pseudotooth birds all along, as they were established based on skull fossils preserving parts of the "toothed" beak.〔Lanham (1947), Brodkorb (1963: pp.262–263), Olson (1985: p.198), Mlíkovský (2002: p.81), Rincón R. & Stucchi (2003), paleocene-mammals.de (2008), Mayr (2009: pp.55–59)〕 One of the species typically placed here – though in fact one that is rather unlikely to actually belong in ''Pseudodontornis'' – is the only smallish pseudotooth bird species known with certainty from the Neogene as of 2009. However, the enigmatic ''Tympanonesiotes'' was of similar size and may also be of Neogene age.〔Scarlett (1972), ''contra'' Mayr (2009: p.59); Hopson (1964), Bourdon (2005)〕 ==Type species and description== The type species ''P. longirostris'' (initially placed in ''Odontopteryx'') is known from an incomplete but quite well preserved〔By the standards of pseudotooth birds at least, whose bones were notoriously thin-walled and fragile and whose fossils are typically crushed and broken: Olson (1985: pp.194–195).〕 fossil skull of unknown age and origin; it was bought from a merchant who had acquired it from a sailor returning from Brazil, but the specimen is widely presumed to be actually from the North Sea region. It is tentatively assigned an Eocene age, if only due to the fact that suitable lagerstätten of different age were not known when the specimen was discovered. If not from Europe however, its age is truly undeterminable. A pseudotooth bird's lower right dentary piece (specimen YPM 4617) from near Charleston, South Carolina (United States) – apparently dredged up from near the source of the Stono River – was provisionally assigned to ''P. longirostris'' as it closely matches the holotype in size and appearance. At first the South Carolina fossil was believed to be from the Early Miocene Hawthorne Formation, but in fact no Hawthorne Formation sediments were known in the Charleston region when the fossil was found. Consequently, modern authors consider a Chattian (Late Oligocene) age more likely and suggest the fossil came from the Cooper or Chandler Bridge Formation. Some fossil remains from the Middle Miocene Bahía Inglesa Formation of Chile were prematurely affiliated with ''P. longirostris'' in error; they are, if anything, of ''Pelagornis''.〔Hopson (1964), Olson (1985: pp.196–198), Matsuoka ''et al.'' (1998), Mlíkovský (2002: p.82), Rincón R. & Stucchi (2003), paleocene-mammals.de (2008)〕 The holotype skull seems to have been lost, but judging from the description the genus might actually be a junior synonym of the (probably) Late Oligocene ''Palaeochenoides'', or either or both might properly belong in the otherwise Miocene ''Pelagornis''. Like in that latter genus, between each two of ''P. longirostris'' large "teeth" was a single smaller one; whether there were even smaller points in addition as in ''Pelagornis'' allopatric contemporary ''Osteodontornis'' cannot be ascertained. Its paroccipital process is not as markedly elongated back- and downwards as in the Ypresian (Early Eocene) ''Dasornis'' and ''Odontopteryx'' and seems to be in a more apomorphic condition, which would agree with a late Paleogene, possibly even (like ''Pelagornis'') Neogene age for the holotype. Its quadrate bone had a broad main shaft like in ''Odontopteryx'' which like in that genus bore a broad lateral ridge that was not, however, curved, but straight as in ''Osteodontornis''; like in that genus, the forward center of the quadrate's ventral articulation ridge extended upwards. Unlike in either ''Odontopteryx'' or ''Osteodontornis'', the quadrate of ''P. longirostris'' had a socket for the quadratojugal that was displaced dorsally. However its relationships may be, there can be no doubt that the mysterious skull was from one of the large pelagornithids, and the living bird must have had a wingspan of more than 5, quite possibly as much as 6 m (16–20 ft).〔Hopson (1964), Olson (1985: p.198), Ono (1989), Matsuoka ''et al.'' (1998), Mayr (2008)〕 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「Pseudodontornis」の詳細全文を読む スポンサード リンク
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