Species: gregorii CHATTERJEE, 2002
Etymology: In honor of Professor Joseph T. Gregory for his contributions to vertebrate Paleontology.

Holotype: TTU P 9265

Locality: Central valley of Seymour Island, near the cost of Lopex de Bertodano Bay, below James Ross Island, Northeast Peninsula, West Antarctica, Antarctica.

Horizon: Sandwich Bluff Member, Lopez de Bartodano Formation.

Biostratigraphy: Unit 9.

Age: Maastrichtian Stage, Upper Senonian Subepoch, Upper Gulf Epoch, Late Cretaceous.

Material: Fragmentary skull, 4 cervical vertebrae, complete left femur, proximal half of a left tibiotarsus, proximal part of a right femur and a sternal fragment.

Note: Polarornis has a pathology on the tibial shaft. Macroscopic and radiological research whowed the tibial shaft has lesions both interally and externally. There is no evidence of healing but periosteal reaction. This is similar to hypertrophic osteoarthropathy as seen in extant avian viral disease.