Presbyornis pervetus (Wetmore 1926; Olson and Feduccia 1980; earliest Eocene, 62 mya) is one of the first of the clade Anseriformes (ducks, geese and kin). It is known from scattered bones and was originally considered a flamingo relative, due to its long legs. The duck-like skull was found later. Long legs mark all basal birds.

Anas platyrhynchos (Linneaus 1758) is the extant mallard duck with shorter legs than Presbyornis. This toothless bird has tooth-like serrations on the keratin that covers its broad bill.

Anser anser (Linneaus 1758; recent 1 m tall) is the extant Greylag goose. It has a shorter rostrum than the duck. Note the pubic boot.

Cygnus olor (Bechstein 1803, orignally Anas olor Gmelin 1789, up to 0.5m tall) is the extant mute swan, one of the heaviest flying birds (up to 32 lbs or 14 kg). Here it is a sister to goose, Anser. The long neck is a primitive trait found in Presbyornis.

Asteriornis maastrichtensis (Field et al. 2020; latest Cretaceous, 66 mya; NHMM 2013 008) was originally considered basal to chickens and geese, but here nests as a sister to the giant filghtless goose, Cnemiornis. The authors reported, "The fossil represents one of the only well-supported crown birds from the Mesozoic era." Note the fused lacrimal + prefrontal, the robust postfrontal + postorbital that together separate the orbit from the antorbital fenestra and temporal fenestrae, that connect with one another as in Cnemiornis. Contra the conclusion of Field et a. 2020, the presence of this highly derived bird taxon in latest Cretaceous strata indicates that all taxa that came before it had Cretaceous roots. This is confirmed by the presence of Paleocene penguins.

Bechstein JM 1803. Ornithologisches Taschenbuch Deutschland 2:404 .

Field DJ, Benito J, Chen A, Jagt JWM and Ksepka DT 2020. Late Cretaceous neornithine from Europe illuminates the origins of crown birds. Nature 579:397–401.

Gmelin JF 1789. Caroli a Linné ... Systema Naturae per Regna Tria Naturae, Secundum Classes, Ordines, Genera, Species, Cum Characteribus, Differentiis, Synonymis, Locis. Editio Decima Tertia, Aucta, Reformata/ cura Jo. Frid. Gmelin. Volume 1, part 3. Lipsiae: Impensis Georg. Emanuel. Beer.

Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

Olson SL and Feduccia A 1980. Presbyornis and the origin of the Anseriformes (Aves: Charadriomorphae). Smithsonian Contributions to Zoology 323: 1–24.

Owen R 1866. XI. On Dinornis (Part X.): containing a Description of part of the Skeleton of a flightless Bird indicative of a New Genus and Species (Cnemiornis calcitrans, Ow.) Journal of Zoology 1866 The Zoological Society of London.

Wetmore A 1926. Fossil birds from the Green River deposits of Eastern Utah. Annals of the Carnegie Museum 16: 391-402.

wiki/Anas
wiki/Presbyornis
wiki/Cnemiornis
wiki/Anser
wiki/Asteriornis
wiki/Cygnus - Mute Swan