Flightless seabirds hint at highly flying ancestor
Klallamornis by FunkMonk. Note that, unlike its modern relatives (cormorants, sulids and anhingas), there is only webbing between three toes instead of all four.
A recent study describes a new plotopterid, Fucadytes. Plotopterids were flightless seabirds that lived from the Eocene to early Miocene in the North Pacific and are often compared to penguins due to similar adaptations for wing-propelled diving, but are instead part of Suliformes, a clade that includes modern sulids, cormorants, anhingas/darters and frigatebirds. Some extinct species achieved large sizes, as tall as a human being.
The study does clarify plotopterid phylogeny, including validating a derived clade known as Tonsalinae, but also draws attention to one fact: the hallux of plotopterids is more similar to that of frigatebirds than that of sulids, cormorants and darters. This means that, unlike them, there was reduced if any webbing between the hallux and the other toes.
This makes sense, as unlike most of their modern relatives plotopterids used their wings rather than their feet to propel themselves around, but the authors of the paper also infer that the ancestral suliform was a highly aerial bird similar to frigatebirds, that subsequently gave rise to different waves of modern aquatic birds. This is interesting because it gives insight into how aquatic propulsion arrises in birds: birds with well developed wings naturally would give rise to wing-propelled divers, as seen with diving petrels and auks (the later are related to the soaring skuas and gulls), while those already somewhat aquatic give rise to foot propelled divers, like waterfowl and grebes.
This is an excellent tool for speculative evolution and how birds would develop their swimming styles.
