Presbyornis

Presbyornis Temporal range: Paleocene-Eocene, 62–55 Ma PreЄ Є O S D C P T J K Pg N (possible Oligocene record)
An assemblage of Presbyornis pervetus skeletons (AMNH 28505)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Anseriformes
Family:	Presbyornithidae
Genus:	Presbyornis Wetmore, 1926
Species
P. pervetus Wetmore, 1926 (type) P. recurvirostris (Hardy, 1959; disputed) P. isoni Olson, 1994
Synonyms
Nautilornis Wetmore, 1926 Coltonia Hardy, 1959

Presbyornis is an extinct genus of anseriform bird. It contains two unequivocally accepted species; the well-known P. pervetus and the much lesser-known P. isoni. P. pervetus was approximately the size and shape of a goose, but with longer legs; P. isoni, known from a few bones, was much larger, more than swan-sized. Other fossils, more doubtfully assigned to this genus, are also known.

The fossil record of P. pervetus includes many complete skeletons from Green River Formation sites (Early Eocene), suggesting that the birds nested in colonies and possibly were liable to succumb to botulism, similar to many colony-nesting waterfowl or shorebirds today. P. isoni is known from the Late Paleocene Aquia Formation (Maryland, 61-62 MYA) humerus (USNM 294116) and a fingerbone (USNM 294117) that were initially described, as well as from the humeri that were initially believed to be from Headonornis (BMNH PAL 3686, 5105, 6240). As these are Late Eocene or even Early Oligocene (BMNH PAL 5105, Bembridge Marls) in age, they possibly belong to a distinct taxon.

P. recurvirostris is a disputed species possibly synonymous with P. pervetus; it is known from a partial wing (KUVP 10105) found in Colton Formation Eocene sediments of the Wasatch Plateau near Ephraim, Utah. Undescribed fossils are also known from the Paleocene of Utah and possibly the Early Eocene of Mongolia. The coracoid still assigned to Headonornis may also belong into this genus.