Interestingly, Vegaviidae is neither called a family anywhere in the paper, nor is it given a phylogenetic definition – even though there's a "type" genus, a list of included taxa and a diagnosis. Evidently the name is not meant to belong to either rank-based or phylogenetic nomenclature, even though the authors would clearly like future works to use this name in a consistent way.
(The lack of registration in ZooBank is consistent with this, but of course doesn't mean much.)
Federico L. Agnolín, Federico Brissón Egli, Sankar Chatterjee, Jordi Alexis Garcia Marsà & Fernando E. Novas (2017)
Vegaviidae, a new clade of southern diving birds that survived the K/T boundary.
The Science of Nature 104:87 (advance online publication)