Aechmophorus occiidentalis (Lawrence 1858; up to 72cm tall) is the extant Western grebe. Like the unrelated flamingo, it has 23 presacral vertebrae, mostly in the long neck. Like the loon, Gavia, the grebe is a diver, paddling with its hind limbs underwater. Mating rituals are astounding.

Anhinga anhinga (Linneaus 1766; 89cm) is the extant snakebird, which swims underwater and stabs its fish prey with its sharp beak, striking like a snake. It breathes only through the mouth as the nostrils are overgrown. The feathers do not shed water, so some time is spent drying the feathers prior to flying.

Sequiwaimanu rosieae (Mayr et al. 2018; middle Paleocene) was described as the best preserved Paleocene penguin, but here this taxon nests with grebes (above) as a penguin mimic. No grebes were tested in the original paper. Finding such a derived taxon in the Paleocene indicates a Cretaceous radiation of crown birds or a more rapid radiation following the K-Pg extinction event. The neck length is unknown at present.

Forster JR 1788. Enchiridion historiae naturali inserviens, quo termini et delineationes ad avium, piscium, insectorum et plantarum adumbrationes intelligendas et concinnandas, secundum methodum systematis Linnaeani continentur. - pp. 1-224. Halae. (Hemmerde & Schwetschke).

Hackett S et al. 2008. A phylogenetic study of birds reveals their evolutionary history. Science 320:1763–1768.

Lawrence 1858. Rep.Expl. Surv.RR.Pac. 9 p.liv, 894.

Linneaus C von 1766. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio duodecima, reformata. pp. 1–532. Holmiæ. (Salvius) .

Mayr GVL, De Pietr L. Love L, Mannering AA and Scofield RP 2018. A well-preserved new mid-Paleocene penguin (Aves, Sphenisciformes) from the Waipara Greensand in New Zealand. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1398169.

wiki/Gavia
wiki/Anhinga
wiki/Sequiwaimanu