Select a thumbnail representing one of the 40 currently described bird orders, from Struthioniformes (bottom left) to Passeriformes (top right). Each order is a clade, i.e., it groups a set of species derived from one common ancestor. Orders should be monophyletic, so that they comprise all the descendants of their common ancestor and these descendants only.

In turn, the 40 bird orders are derived, not from each other, but from a set of more ancestral precursors. Click on the yellow labels to display the cladograms generating the precursors of the 40 orders. Again, each of these trees is a monophyletic clade, as defined above.

Internauts interested in the cladistic classification of birds may select this link.. The studies by Hackett et al (2008) and Yuri et al (2013), together with the related IOC World Bird List (2012) describe how cladistics classifies the ~ 10 500 bird species into 40 orders, replacing former nomenclatures which counted less than 30 orders.