Most traditional "crane-form" birds are not true Gruiformes
Gruiformes means crane-form, and for a century taxonomists dumped odd waders into the order for lack of a better shelf. Molecular work now says only the core Grues—cranes, rails, trumpeters, limpkin, finfoots, flufftails, and extinct adzebills—are genuine. Kagu, sunbittern, bustards, and button-quails belong elsewhere.
Max Fürbringer's 1888 anatomy cemented a catch-all order: about fifteen crane species, roughly one hundred forty-five rails and crakes, plus tiny families such as Heliornithidae, Aramidae, and Psophiidae. Birds that fit nowhere else piled in, so the expanded order lacked shared apomorphies. Olson and Steadman in 1981 correctly pulled the Australian plains-wanderer into shorebirds; DNA hybridization and later multi-locus studies confirmed button-quails as Charadriiformes too. By the 2000s, Fain, Houde, Ericson, and Hackett showed traditional Gruiformes hold five to seven unrelated clades.
Core Grues unite Rallidae, Sarothruridae, Heliornithidae, Aptornithidae, Psophiidae, Aramidae, and Gruidae—the only true Gruiformes. Eurypygae pairs kagu with sunbittern—close to each other, not to cranes—and mesites, seriemas, and bustards each form separate Neoaves lineages. Fain and Houde's Metaves–Coronaves split places sunbittern, kagu, and mesites with Metaves while other former "gruiforms" scatter among waterbirds or landbirds in Coronaves, though mitochondrial DNA complicates clean Coronaves monophyly when few families are sampled and sequences saturate at deep divergences.
Gondwanan storylines once tied kagu, sunbittern, and New Zealand adzebills together; molecular dates say kagu and sunbittern split long after Gondwana broke, while adzebills nest inside Grues. Many extinct families look crane-like on paper, from phorusrhacids to eogruids and messelornithids, yet none can be confidently placed in core Gruiformes. The lesson is editorial as much as evolutionary: a tidy Latin order can hide a polyphyletic attic until genes force a clear-out of the crane-form label.
Source: Gruiformes
