Pelecaniformes

The Pelecaniformes is an order of birds that includes the pelicans (Pelecanidae), the shoebill (Balaeniceps rex), the hammerhead (Scopus umbretta), the herons (Ardeidae), and the ibises and spoonbills (Threskiornithidae).

Until a few years ago the order had an almost entirely different composition, and besides the pelicans the boobies (Sulidae), the frigate birds (Fregatidae), the tropic birds (Phaethontidae), the cormorants (Phalacrocoracidae), and the darters (Anhingidae) were placed in the Pelecaniformes. In this composition the Pelecaniformes were called in German Ruderfüßer, after the construction of the feet, in which all four toes are connected by a web. However, the similarities between pelicans and the other families are based only on convergence, molecular biological findings such as DNA comparisons of mitochondrial and nuclear (located in the nucleus) DNA speak clearly against a relationship.

The closest relatives of the pelicans, on the other hand, are the shoebill (Balaeniceps rex) and the hammerhead (Scopus umbretta), two birds that are native to tropical Africa and are counted among the walking birds (Ciconiiformes) in traditional systematics. Sister group of the clade formed by all three taxa are the herons (Ardeidae) and the ibises and spoonbills (Threskiornithidae). Sister group of the clade formed by all five taxa are the remaining copepods. Returning to monophyletic taxa, the International Ornithological Committee assigns all families of walking birds except the storks (Ciconiidae) to the Pelecaniformes. The tropicbirds now form an independent order, the Phaethontiformes and the other millipedes are placed in the order Suliformes.

The close relationship of the families now placed in the Pelecaniformes is based on molecular biological studies and is not yet supported by morphological characteristics.

The following cladogram shows the probable family relationships.