Polarornis - AbsoluteAstronomy.com

Polarornis is a genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

of prehistoric bird

Bird

Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

, possibly a loon

Loon

The loons or divers are a group of aquatic birds found in many parts of North America and northern Eurasia...

. It contains a single species Polarornis gregorii known from incomplete remains of one individual found on Seymour Island

Seymour Island

Seymour 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 closer to continental land mass than any other part of that Antarctica. It lies within the section of the island chain that resides off the west side of the...

, Antarctica, in rocks which are dated to the Late Cretaceous

Late Cretaceous

The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...

(López de Bertodano Formation

Lopez de Bertodano Formation

The Lopez de Bertodano Formation is a geological formation in the James Ross archipelago of the Antarctic Peninsula. The strata date to the end of the Late Cretaceous , about 70-65 million years ago. Dinosaur remains are among the fossils that have been recovered from the formation....

, about 65 mya).

The discovery of Polarornis gregorii was first announced by Sankar Chatterjee

Sankar Chatterjee

Sankar Chatterjee 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 Calcutta in 1970 and was a Post-doctoral Fellow at the Smithsonian...

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.

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. Before the official description of the species, Alan Feduccia published an opinions casting doubt on its identification as a loon. 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.

Paleobiology

Polarornis was in all likelihood aquatic

Aquatic animal

An aquatic animal is an animal, either vertebrate or invertebrate, which lives in water for most or all of its life. It may breathe air or extract its oxygen from that dissolved in water through specialised organs called gills, or directly through its skin. Natural environments and the animals that...

and fed on fish and large invertebrates, probably being an ecological equivalent of loons, grebes, or the Cretaceous Hesperornithes

Hesperornithes

Hesperornithes is an extinct and highly specialized clade of Cretaceous toothed birds. Hesperornithine birds, apparently limited to former aquatic habitats in the Northern Hemisphere, include genera such as Hesperornis, Parahesperornis, Baptornis, Enaliornis, and probably Potamornis, all...

of the Northern Hemisphere

Northern Hemisphere

The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...

. One analysis of the structure of the femur

Femur

The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...

(TTU

Texas Tech University

Texas Tech University, often referred to as Texas Tech or TTU, is a public research university in Lubbock, Texas, United States. Established on February 10, 1923, and originally known as Texas Technological College, it is the leading institution of the Texas Tech University System and has the...

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

Penguin

Penguins are a group of aquatic, flightless birds living almost exclusively in the southern hemisphere, especially in Antarctica. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have become flippers...

Classification

Paleobiology

Further reading