The classification appears to be an early example of cladistic classification[clarification needed] because it codifies many intermediate levels of taxa: the "trunk" of the family tree is the class Aves, which branches into subclasses, which branch into infraclasses, and then "parvclasses", superorders, orders, suborders, infraorders, "parvorders", superfamilies, families, subfamilies, tribes, subtribes and finally genera and species.
However the classification study did not employ modern cladistic methods, as it relies strictly on DNA-DNA hybridization as the sole measure of similarity.
Other birds [2] Anseriformes Galliformes Craciformes Showing major changes from Clements, the Sibley–Ahlquist orders are as follows: Some of these changes are minor adjustments.
Sibley and Ahlquist, though, put penguins in the same superfamily as divers (loons), tubenoses, and frigatebirds.
The DNA evidence of Sibley–Ahlquist for the monophyly of the group is supported by the discovery of the fossil bird Vegavis iaai, an essentially modern but most peculiar waterfowl that lived near Cape Horn some 66–68 million years ago, still in the age of the dinosaurs.