Mirandornithes is a clade

Clade

A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

 that consists of flamingos and grebes. The relationships of both groups have been problematic. Flamingos had been placed with numerous branches within Neognathae

Neognathae

Neognaths are birds within the subclass Neornithes of the class Aves. The Neognathae include virtually all living birds; their sister taxon Palaeognathae contains the tinamous and the flightless ratites....

, such as ducks and storks. The grebes had been placed with the loon

Loon

The loons or divers are a group of aquatic birds found in many parts of North America and northern Eurasia...

s. However recent studies seem to confirm these two branches as sister groups.