[1] Regarding the recent evidence that the traditional Pelecaniformes is polyphyletic,[2] it has been suggested that the group be divided to reflect the true evolutionary relationships; a 2017 study indicated that they are most closely related to Otidiformes (bustards) and Ciconiiformes (storks).

[3] According to Hackett et al. (2008), loons, penguins, storks, and as well as Suliformes and Pelecaniformes, all seem to have evolved from a common ancestor.

In 1994, American ornithologist Walter J. Bock wrote that the name Suloidea had been used consistently as a term for a superfamily containing the two families, so therefore "Sulidae" and not "Phalacrocoracidae" should take priority in any arrangement containing the two genera.

[8] In 1994, Martyn Kennedy and colleagues constructed a behavioural data set, with the resulting tree showing a high level of congruence with existing phylogenies based on genetics or morphology.

It showed the darters as sister group to the cormorants and shags, with the gannets and boobies, then pelicans, then frigatebirds and lastly tropicbirds as progressively earlier offshoots.