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Polarornis
''Polarornis'' is a genus of prehistoric bird, possibly a loon. It contains a single species ''Polarornis gregorii'' known from incomplete remains of one individual found on Seymour Island, Antarctica, in rocks which are dated to the Late Cretaceous (López de Bertodano Formation, about 66 mya).
The discovery of ''Polarornis gregorii'' was first announced by Sankar Chatterjee in 1989, but he did not describe and officially name the species until 2002.〔Chatterjee, S. (1989). "The oldest Antarctic bird." ''Journal of Vertebrate Paleontology'', 8(3): 11A.〕〔Chatterjee, S. (2002). "The morphology and systematics of ''Polarornis'', a Cretaceous loon (Aves: Gaviidae) from Antarctica." Pp. 125-155 in Zhou and Zhang (eds), ''Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution, Beijing, 1-4 June 2000''. Beijing: Science Press.〕 The name ''Polarornis'' had been announced unofficially several years prior to its official publication, in Chatterjee's 1997 book ''The Rise of Birds''.〔Chatterjee, S. (1997). ''The Rise of Birds''. Baltimore: Johns Hopkins University Press.〕
==Classification==
The relationships of this species are unclear. It is often claimed to be an ancestor of modern loons (divers), but some scientists have questioned this. Gerald Mayr, for example, noted that ''Polarornis'' differed from loons in some important characteristics, and criticized Chatterjee's original description of the fossils for overstating the specimen's completeness.〔Mayr, G. 2004. "A partial skeleton of a new fossil loon (Aves, Gaviiformes) from the early Oligocene of Germany with preserved stomach content." ''Journal of Ornithology'' 145: 281–286. (PDf fulltext )〕 Before the official description of the species, Alan Feduccia published an opinions casting doubt on its identification as a loon.〔Feduccia, A. (1999). ''The Origin and Evolution of Birds''. 2nd edition. Yale University Press.〕 However, other Mesozoic bird specialists, including Storrs Olson and Sylvia Hope, have supported the classification of ''Polarornis'' as an early member of the loon lineage.〔Olson, S. (1992). "''Neogaeornis wetzeli'' Lambrecht, a Cretaceous loon from Chile (Aves, Gaviidae)." ''Journal of Vertebrate Paleontology,'' 12(1): 122-124.〕〔Hope, S. (2002). "The Mesozoic radiation of Neornithes." Pp. 339-388 in Chiappe, L.M. and Witmer, L. (eds.), ''Mesozoic Birds: Above the Heads of Dinosaurs''.〕
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