If like me you owned a field guide at the turn of the century you remember that loons were the first bird in the book. Ornithologists placed them there because they thought loons were the oldest evolved bird in North America but DNA sequencing changed all that. In 2020 loons are near the middle of the tree and they have unexpected relatives.
In this July 2019 phylogenetic supertree I’ve circled loons and their relatives in blue. Notice that they aren’t related to ducks at all. Ducks are related to chickens.
Here’s a closer look at the blue section showing that loons (Gaviiformes) stand alone after they split from a common ancestor of penguins, tubenoses, storks, cormorants and pelicans.