Tropicbirds were traditionally grouped in the gannets and boobies and frigatebirds; in the Sibley-Ahlquist taxonomy, the Pelecaniformes were united with other groups into a large " Ciconiiformes ".
22.
In response to these findings, the International Ornithological Congress ( IOC ) recently reclassified Ardeidae and their sister taxa Threskiornithidae under the order Pelecaniformes instead of the previous order of Ciconiiformes.
23.
Molecular studies have consistently shown that pelicans, the namesake family of the Pelecaniformes, are actually more closely related to herons, order comprising the frigatebirds and Suloidea was renamed Suliformes in 2010.
24.
The Pelecaniformes in particular have a distinct hook or " nail " on the billtip, which is even present in the otherwise plesiomorphic bill of the hammerkop ( " Scopus umbretta " ).
25.
The classification of this group as the traditional Pelecaniformes, united by feet that are totipalmate ( with all four toes linked by webbing ) and the presence of a gular pouch, persisted until the early 1990s.
26.
Long thought to be related to frigatebirds, cormorants, tropicbirds, gannets and boobies, pelicans instead are now known to be most closely related to the shoebill and hamerkop, and are placed in the order Pelecaniformes.
27.
In any case, this species ( as well as " Torotix " ) seem to have been seabirds, most probably relatives of the Procellariiformes and / or some lineage of the paraphyletic " Pelecaniformes ".
28.
But pelicans, the namesake family of the Pelecaniformes, are actually closer related to herons, Phalacrocoraciformes, which also includes the frigatebirds ( Fregatidae ) as well as one or more prehistoric lineages that are entirely extinct today.
29.
Most unrecognised pelagornithid bones were initially assigned to " higher waterbird " families however, typically to the ( then-paraphyletic ) " Pelecaniformes ", but in particular the tarsometatarsus was typically mistaken for that of a procellariiform.
30.
Martyn Kennedy and colleagues derived a cladogram based on behavioural characteristics of the traditional Pelecaniformes, calculating the frigatebirds to be more divergent than pelicans from a core group of gannets, darters and cormorants, and tropicbirds the most distant lineage.
