This order contains but a single family, the Podicipedidae or grebes, with 20 extant species. So far the intrafamilial phylogeny hasn't been investigated with molecular methods.
Grebes are a group of freshwater diving birds that exhibit profound convergencies with loons, family Gaviidae (as well as
Some species are poor flyers, two species are entirely flightless (Rollandia microptera, Podiceps taczanowskii).
Horned Grebe (Podiceps auritus) in non-breeding plumage.
Fjeldså, J. (2004), “The Grebes: Podicipedidae”, Oxford University Press, Oxford.