name = "Polarornis"
fossil_range = Late
genus = "Polarornis"
species = "P. gregorii "
binomial = "Polarornis gregorii"
"Polarornis" [It is sometimes suggested that this taxon was never formally described correctly and thus a "
nomen nudum", but this is not true.Fact|date=April 2007] is a controversial (see Mayr, 2002) genusof prehistoric bird. It contains a single species "Polarornis gregorii" known from incomplete remains of one individual [Often claimed to be found in association, i.e. laid out in the pattern of a living bird. This is possibly incorrect, as indicated by the fact that e.g. two leg bones were found but the entire pelvisand most of the vertebral columnwas not.] found on Seymour Island, Antarctica, in rocks which are claimed to be of Late Cretaceous( López de Bertodano Formation, c. 76 mya) origin by supporters of the bird's antiquity, but may be no older than Eoceneor about 50 mya.
The relationships of this taxon are unclear. It is not infrequently claimed to be an ancestor of modern
loons(divers), but this is not necessarily correct as the material is not very diagnostic and the reconstructions take very much leeway to depict this bird as a primitive loon. What can be said with a reasonable degree of certainty is that it was in all likelihood aquatic and fed on fish and large invertebrates, probably being an ecological equivalent of loons, grebes, or the Cretaceous Hesperornithesof the Northern Hemisphere. Analysis of the structure of a femur(TTU P 9265) indicates that "Polarornis" was a flightless or near-flightless diving bird along the lines of the Hesperornithes or penguins, making a direct connection with modern looks highly unlikely (Chinsamy "et al." 1998).
The theory has been proposedFact|date=February 2007 that "Polarornis" represents a
Southern Hemisphereradiation of loon ancestors which filled the same ecological nicheas the Hesperornithes and might even have prevented them from spreading southwards. Although conjectural, as clearly recognizable loons do not appear in the fossil record until the Late Eocene(some 35 mya), this theory is not entirely without merit: the Late Cretaceous genus " Neogaeornis" and " Lonchodytes" may be ancestral loons - indeed, the former is sometimes considered synonymous with "Polarornis" - which are known from South and North American locations, respectively. However, both are alternatively considered to be Hesperornithes or other seabirds; at any rate, there is no unequivocal proof that loons "ever" occurred in the Southern Hemisphere, and the overwhelming majority of evidence clearly points to a Western European origin of the order (see Loonfor details).
It is notable that Eocene penguins from Seymour Island are somewhat intermediate between modern penguins and loons in the characters of their skull (Olson, 1985), and the least controversial interpretation of "Polarornis" is to consider it a basal neognathe bird of a lineage which later evolved into some sort(s) of seabirds like loons and/or penguins. The possibility that it is a non-neornithine cannot be ruled out completely at present.
Biogeographyof avian survivorship of the Cretaceous–Tertiary extinction eventcoupled with new data on avian phylogeny(e.g. Fain & Houde 2004) suggests that survival of at least one, more probably some, southern Pacific lineage(s) of Neoavesis indeed likely. The possibility that "Polarornis" represents a valid Mesozoictaxon in some kind of basal relationship to any or all of such birds as plotopterids, cormorants, albatrosses, penguins, storks and/or loons is likely enough to warrant more research of the remains.
* Chinsamy, A.; Martin, Larry D. & Dobson, P. (1998): Bone microstructure of the diving "Hesperornis" and the volant "Ichthyornis" from the Niobrara Chalk of western Kansas. "Cretaceous Research" 19(2): 225-235. DOI|10.1006/cres.1997.0102 (HTML abstract)
* Fain, Matthew G. & Houde, Peter (2004): Parallel radiations in the primary clades of birds. "Evolution" 58(11): 2558-2573. DOI|10.1554/04-235 [http://biology-web.nmsu.edu/houde/Parallel_radiations.pdf PDF fulltext]
* Mayr, Gerald (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. DOI|10.1007/s10336-004-0050-9 [http://www.senckenberg.de/files/content/forschung/abteilung/terrzool/ornithologie/colymboides.pdf PDf fulltext]
* Olson, Storrs L. (1985): The fossil record of birds. "In:" Farner, D.S.; King, J.R. & Parkes, Kenneth C. (eds.): "Avian Biology" 8: 79-238. Academic Press, New York.
Wikimedia Foundation. 2010.
Look at other dictionaries:
Neogaeornis — Temporal range: Late Cretaceous Scientific classification Kingdom: Animalia Phylum: Chordata Class … Wikipedia
Loon — For other uses, see Loon (disambiguation). Divers / Loons Temporal range: ?Late Eocene Recent (see text) 37–0 Ma … Wikipedia
List of fossil birds — Birds are generally believed to have evolved from certain feathered theropod dinosaurs, and there is no real dividing line between birds and dinosaurs, except of course that some of the former survived the Cretaceous Tertiary extinction event… … Wikipedia
Gavia — Seetaucher Eistaucher (Gavia immer) Systematik Reihe: Landwirbeltiere (Tetrapoda) Klasse … Deutsch Wikipedia
Gaviidae — Seetaucher Eistaucher (Gavia immer) Systematik Reihe: Landwirbeltiere (Tetrapoda) Klasse … Deutsch Wikipedia
Liste ausgestorbener Vögel — Die prähistorisch im späten Quartär ausgestorbenen und meist nur unvollständig fossilisierten Vogeltaxa sind unter Spätquartäre Avifauna aufgeführt. Die seit 1500 ausgestorbenen Vogeltaxa finden sich unter Liste der neuzeitlich ausgestorbenen… … Deutsch Wikipedia
Seetaucher — Eistaucher (Gavia immer) Systematik Reihe: Landwirbeltiere (Tetrapoda) Klasse: Vögel (Aves) … Deutsch Wikipedia
Seetaucherartige — Seetaucher Eistaucher (Gavia immer) Systematik Reihe: Landwirbeltiere (Tetrapoda) Klasse … Deutsch Wikipedia