''Polarornis'' is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of prehistoric
bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
, possibly an
anserimorph. It contains a single species ''Polarornis gregorii'', known from incomplete remains of one individual found on
Seymour Island
Seymour Island or Marambio Island, is an island in the chain of 16 major islands around the tip of the Graham Land on the Antarctic Peninsula. Graham Land is the closest part of Antarctica to South America. It lies within the section of the isla ...
,
Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
, in rocks which are dated to the
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...
(
López de Bertodano Formation
The Lopez de Bertodano Formation is a geological Formation (geology), formation in the James Ross Island, James Ross archipelago of the Antarctic Peninsula. The strata date from the end of the Late Cretaceous (upper-lower Maastrichtian stage) to t ...
, about 66
Ma).
The discovery of ''Polarornis gregorii'' was first announced by
Sankar Chatterjee
Sankar Chatterjee (born May 28, 1943) is a paleontologist, and is the Paul W. Horn Professor of Geosciences at Texas Tech University and Curator of Paleontology at the Museum of Texas Tech University. He earned his Ph. D. from the University of ...
in 1989, but he did not describe and officially name the species until 2002.
[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
Loons ( North American English) or divers (British / Irish English) are a group of aquatic birds found in much of North America and northern Eurasia. All living species of loons are members of the genus ''Gavia'', family Gaviidae and order ...
(divers), but some scientists have questioned this.
Gerald Mayr
Gerald Mayr is a German palaeontologist who is Curator of Ornithology at the Senckenberg Research Institute in Frankfurt am Main, Hesse. He has published extensively on fossil birds, especially the Paleogene avifauna of Europe. He is an expert on ...
, 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.
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.
[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'']
Some recent studies seem to vindicate its status as a stem-
loon
Loons (North American English) or divers (British / Irish English) are a group of aquatic birds found in much of North America and northern Eurasia. All living species of loons are members of the genus ''Gavia'', family Gaviidae and order Gavi ...
;
[Carolina Acosta Hospitaleche, Javier N. Gelfo, New Antarctic findings of Upper Cretaceous and lower Eocene loons (Aves: Gaviiformes), Annales de Paléontologie Volume 101, Issue 4, October–December 2015, Pages 315–324] alongside ''
Neogaeornis
''Neogaeornis'' is a controversial prehistoric genus of diving bird. The single known species, ''Neogaeornis wetzeli'', was described from fossils found in the Campanian to Maastrichtian Quiriquina Formation of Chile. It lived about 70-67 million ...
'' and some unnamed
Antarctic
The Antarctic ( or , American English also or ; commonly ) is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and other ...
specimens, it seems to suggest a
Gondwana
Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...
n origin for this clade, possibly displaced northwards by early
penguins
Penguins ( order Sphenisciformes , family Spheniscidae ) are a group of aquatic flightless birds. They live almost exclusively in the Southern Hemisphere: only one species, the Galápagos penguin, is found north of the Equator. Highly adapt ...
. However, in 2017, a phylogenetic study, Agnolín and colleagues have found ''Neogaeornis'' and ''Polarornis'' to be stem-
anseriform
Anseriformes is an order of birds also known as waterfowl that comprises about 180 living species of birds in three families: Anhimidae (three species of screamers), Anseranatidae (the magpie goose), and Anatidae, the largest family, which inc ...
s along with ''
Australornis
''Australornis'' (Latin: "southern bird") is a genus of extinct seabird discovered in New Zealand. It lived in the Paleocene epoch, 60.5 to 61.6 million years ago (Ma). The type species name originates from ''australis'', Latin for "southern", a ...
'' and ''
Vegavis
''Vegavis'' is a genus of extinct bird that lived during the Late Cretaceous (Maastrichtian stage) of Antarctica, some 68 to 66 mya. Among modern birds, most studies show that ''Vegavis'' is most closely related to ducks and geese (Anatidae), b ...
'' in the family
Vegaviidae
Vegaviidae is an extinct family of ornithurines, often regarded as stem-anseriforms, which existed during the Late Cretaceous and possibly the Paleocene. Fossils attributed to the family have been found in Canada, Chile, New Zealand, and Antarct ...
.
Paleobiology
''Polarornis'' was in all likelihood
aquatic and fed on fish and large
invertebrates
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
, probably being an ecological equivalent of loons, grebes, or the Cretaceous
Hesperornithes
Hesperornithes is an extinct and highly specialized group of aquatic avialans closely related to the ancestors of modern birds. They inhabited both marine and freshwater habitats in the Northern Hemisphere, and include genera such as '' Hesperorn ...
of the
Northern Hemisphere
The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...
. One analysis of the structure of the
femur
The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...
(
TTU P 9265) showed that the bones were dense, rather than hollow and lightweight as in flying birds, suggesting that ''Polarornis'' was a flightless or near-flightless diving bird similar to hesperornithines and
penguin
Penguins (order (biology), order List of Sphenisciformes by population, Sphenisciformes , family (biology), family Spheniscidae ) are a group of Water bird, aquatic flightless birds. They live almost exclusively in the Southern Hemisphere: on ...
s.
See also
*
Geology of Antarctica
The geology of Antarctica covers the geological development of the continent through the Archean, Proterozoic and Phanerozoic eons.
The geological study of Antarctica has been greatly hindered by the fact that nearly all of the continent is c ...
**
List of fossiliferous stratigraphic units in Antarctica
This is a list of fossiliferous stratigraphic units in Antarctica.
__NOTOC__
List of fossiliferous stratigraphic units
See also
* Geology of Antarctica
* List of fossiliferous stratigraphic units in Namibia
* List of fossiliferous st ...
*
South Polar region of the Cretaceous
The South Polar region of the Cretaceous comprised the continent of East Gondwana–modern day Australia and Antarctica–a product of the break-up of Gondwana in the Cretaceous Period. The southern region, during this time, was much warmer than i ...
References
Further reading
*
* 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.
{{Taxonbar, from=Q7209183
Prehistoric bird genera
Extinct flightless birds
Late Cretaceous birds
Cretaceous birds of Antarctica
Fossils of Antarctica
Fossil taxa described in 2002