Plotopteridae[1] is an extinct family of flightless seabirds with uncertain placement, generally considered as member of order Suliformes.

More recent studies have shown, however, that the shoulder-girdle, forelimb and sternum of plotopterids differ significantly from those of penguins, so comparisons in terms of function may not be entirely accurate.

[2] They had shortened wings optimised for underwater wing-propelled pursuit diving (like penguins or the now extinct great auk), and a body skeleton similar to that of the darter.

The second species to be named from rocks along the eastern Pacific Ocean was Tonsala hildegardae[15] from the late Oligocene lower part of the Pysht Formation in Washington State.

More fossils of T. hildegardae have since been described [16][17] and included some of the first known examples of borings made by the marine bone-eating worm Osedax in bird bones.