''Polarornis'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of prehistoric

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

, 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 isl ...

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...

, in rocks which are dated to the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent 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 ''cre ...

(

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 paleontology, paleontologist, the Paul W. Horn Professor of Earth science, Geosciences at Texas Tech University and curator of Paleontology at the Museum of Texas Tech University. He earned his Doctor of ...

in 1989, but he did not describe and officially name the species until 2002. 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. It was about the size of a

common loon The common loon or great northern diver (''Gavia immer'') is a large member of the loon, or diver, family (biology), family of birds. Reproduction, Breeding adults have a plumage that includes a broad black head and neck with a greenish, purpli ...

, measuring long and weighing .

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 Gav ...

(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.Mayr, Gerald (2016). ...

, 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 English, 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 (biolog ...

;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'' and some unnamed

Antarctic The Antarctic (, ; commonly ) is the polar regions of Earth, polar region of Earth that surrounds the South Pole, lying within the Antarctic Circle. It is antipodes, diametrically opposite of the Arctic region around the North Pole. The Antar ...

specimens, it seems to suggest a

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

n origin for this clade, possibly displaced northwards by early

penguins Penguins are a group of aquatic flightless birds from the family Spheniscidae () of the order Sphenisciformes (). They live almost exclusively in the Southern Hemisphere. Only one species, the Galápagos penguin, is equatorial, with a sm ...

. 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'' and ''

Vegavis ''Vegavis'' is a genus of extinct bird that lived in Antarctica during the Maastrichtian stage of the Late Cretaceous. The type and only species is ''Vegavis iaai'', representing one of the earliest known crown group birds. Initially described ...

'' in the family

Vegaviidae Vegaviidae is a proposed extinct family of anseriform birds which lived during the Late Cretaceous and possibly the Paleocene. The monophyly of the family has been questioned by subsequent studies, with the only definitive member ''Vegavis'' know ...

Paleobiology

''Polarornis'' was in all likelihood

aquatic Aquatic means relating to water; living in or near water or taking place in water; does not include groundwater, as "aquatic" implies an environment where plants and animals live. Aquatic(s) may also refer to: * Aquatic animal, either vertebrate ...

and fed on fish and large

invertebrates Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordate subphylum ...

, probably being an ecological equivalent of loons, grebes, or the Cretaceous

Hesperornithes Hesperornithes is an extinct and highly specialized group of aquatic Avialae, avialans closely related to the ancestors of modern birds. They inhabited both marine and freshwater habitats in the Northern Hemisphere, and include genus, genera such ...

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 by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...

. One analysis of the structure of the

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

( 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 are a group of aquatic flightless birds from the family Spheniscidae () of the order Sphenisciformes (). They live almost exclusively in the Southern Hemisphere. Only one species, the Galápagos penguin, is equatorial, with a sm ...

Classification

Paleobiology

See also

References

Further reading