|Crested Crane, Balearica regulorum gibbericeps|
|Global Distribution of the Cranes and allies.|
Traditionally, a number of wading and terrestrial bird families that did not seem to belong to any other order were classified together as Gruiformes. These include 14 species of large cranes, about 145 species of smaller crakes and rails, as well as a variety of families comprising one to three species, such as the Heliornithidae, the limpkin, or the trumpeters. Other birds have been placed in this order more out of necessity to place them somewhere; this has caused the expanded Gruiformes to lack distinctive apomorphies. Recent studies indicate that these "odd Gruiformes" are if at all only loosely related to the cranes, rails, and relatives ("core Gruiformes").
There are only two suprafamilial clades (natural groups) among the birds traditionally classified as Gruiformes. Rails (Rallidae), finfoots and sungrebe (Heliornithidae), adzebills (Aptornithidae), trumpeters (Psophiidae), limpkin (Aramidae), and cranes (Gruidae) compose the suborder Grues and are termed "core-Gruiformes" (Fain et al. 2007). These are the only true Gruiformes. The suborder Eurypygae includes the kagu (Rhynochetidae) and sunbittern (Eurypygidae). These are not even remotely related to Grues. The families of mesites or roatelos (Mesitornithidae), button-quails (Turnicidae), Australian Plains-wanderer (Pedionomidae), seriemas (Cariamidae), and bustards (Otididae) each represent distinct and unrelated lineages. Many families known only from fossils have been assigned to the Gruiformes, e.g., Ergilornithidae, Phorusrhacidae, Messelornithidae, Eogruidae, Idiornithidae, Bathornithidae, to name just a few (see below). In spite of the fact that some of these are superficially 'crane-like' and the possibility that some may even be related to extant families traditionally included in the Gruiformes, there are no completely extinct families that can be confidently assigned to core-Gruiformes.
The traditional order Gruiformes was established by the influential German avian comparative anatomist Max Fürbringer (1888). Over the decades, many ornithologists suggested that members of the order were in fact more closely related to other groups (reviewed by Olson 1985, Sibley and Ahlquist 1990). For example, it was thought that sunbittern might be related to herons and that seriemas might be related to cuckoos. Olson and Steadman (1981) were first to correctly disband any of the traditional Gruiformes. They recognized that the Australian Plains-wanderer (family Pedionomidae) was actually a member of the shorebirds (order Charadriiformes) based on skeletal characters. This was confirmed by Sibley & Ahlquist (1990) based on DNA-DNA hybridization and subsequently by Paton et al. (2003), Paton and Baker (2006) and Fain and Houde (2004, 2006). Sibley and Ahlquist furthermore removed button-quails (Turnicidae) from the Gruifomes based on large DNA-DNA hybridization distances to other supposed Gruiformes. However, it was not until the work of Paton et al. (2004) and Fain and Houde (2004, 2006) that the correct placement of buttonquails within the shorebirds (order Charadriiformes) was documented on the basis of phylogenetic analysis of multiple genetic loci. Using 12S ribosomal DNA sequences, Houde et al. (1997) were the first to present molecular genetic evidence of gruiform polyphyly, although apparently they were not convinced by it. However on the basis of numerous additional sequence data, it has been shown decisively that the traditionally recognized Gruiformes consist of five to seven unrelated clades (Fain and Houde 2004, Ericson et al. 2006, Hackett et al. 2008).
Fain & Houde (2004) proposed that Neoaves are divisible into two clades, Metaves and Coronaves, although it has been suggested from the start that Metaves maybe paraphyletic (Fain and Houde 2004, Ericson et al. 2006, Hackett et al. 2008). Sunbittern, kagu, and mesites all group within Metaves but all the other lineages of "Gruiformes" group either with a collection of waterbirds or landbirds within Coronaves. This division has been upheld by the combined analysis of as many as 30 independent loci (Ericson et al. 2006, Hackett et al. 2008), but is dependent on the inclusion of one or two specific loci in the analyses. One locus, i.e., mitochondrial DNA, contradicts the strict monophyly of Coronaves (Morgan-Richards et al. 2008), but phylogeny reconstruction based on mitochondrial DNA is complicated by the fact that few families have been studied, the sequences are heavily saturated (with back mutations) at deep levels of divergence, and they are plagued by strong base composition bias.
The kagu and sunbittern are one another's closest relatives. It had been proposed (Cracraft 2001) that they and the recently extinct adzebills (family Aptornithidae) from New Zealand constitute a distinct Gondwanan lineage. However, sunbittern and kagu are believed to have diverged from one another long after the break-up of Gondwanaland and the adzebills are in fact members of the Grues (Houde et al. 1997, Houde 2009). The seriemas and bustards represent distinct lineages within neoavian waterbirds.
- Suborder Ralli
- Suborder Grui
- Families incertae sedis and doubtful Gruiformes
- Family †Parvigruidae (fossil)
- Family †Songziidae (fossil)
- Family †Gastornithidae (diatrymas) (fossil)
- Family †Messelornithidae (Messel-birds)
- Family †Salmilidae (fossil)
- Family †Geranoididae (fossil)
- Family †Bathornithidae (fossil) - distinct order (Cariamae)
- Family †Idiornithidae (fossil) - distinct order (Cariamae)
- Family †Phorusrhacidae (terror birds) (fossil) - distinct order (Cariamae)
- Family Cariamidae (seriemas) - Neoavian landbirds - distinct order (Cariamae)
- Family Otididae (bustards) - Neoavian waterbirds - distinct order
- Family Eurypygidae (Sunbittern) - prospective "Metaves" - new order Eurypygiformes together with kagu 
- Family Rhynochetidae (Kagu) - prospective "Metaves" - new order Eurypygiformes together with sunbittern 
- Family Mesitornithidae (mesites, roatelos, monias) prospective "Metaves" - distinct order
When considered to be monophyletic, it was assumed that Gruiformes was among the more ancient of avian lineages. The divergence of "gruiforms" among "Metaves" and "Coronaves" is proposed to be the first divergence among Neoaves, far predating the Cretaceous–Tertiary extinction event c. 65 mya(Houde 2009). No unequivocal basal gruiforms are known from the fossil record. However, there are several genera which are not unequivocally assignable to the known families and which may occupy a more basal position:
- Propelargus (Late Eocene/Early Oligocene of Quercy, France) - cariamid or idornithid
- Rupelrallus (Early Oligocene of Germany) - rallid? parvigruid?
- Badistornis (Brule Middle Oligocene of Shannon County, USA) - aramid?
- Probalearica (Late Oligocene? - Middle Pliocene of Florida, USA, France?, Moldavia and Mongolia) - gruid? A nomen dubium?
- "Gruiformes" gen. et sp. indet. MNZ S42623 (Bathans Early/Middle Miocene of Otago, New Zealand) - Aptornithidae?
- Aramornis (Sheep Creek Middle Miocene of Snake Creek Quarries, USA) - gruid? aramid?
- Euryonotus (Pleistocene of Argentina) - rallid?
- Occitaniavis - cariamid or idiornithid, includes Geranopsis elatus
- Horezmavis (Bissekty Late Cretaceous of Kyzyl Kum, Uzbekistan)
- Telmatornis (Navesink Late Cretaceous?)
- Amitabha (Bridger middle Eocene of Forbidden City, USA) - rallid?
- Eobalearica (Ferghana Late? Eocene of Ferghana, Uzbekistan) - gruid?
- "Phasianus" alfhildae (Washakie B Late Eocene of Haystack Butte, USA)
- Talantatos (Late Eocene of Paris Bain, France)
- Telecrex (Irdin Manha Late Eocene of Chimney Butte, China) - rallid?
- Neornithes incerta sedis (Late Paleocene/Early Eocene of Ouled Abdoun Basin, Morocco)
- Aminornis (Deseado Early Oligocene of Rio Deseado, Argentina) - aramid?
- Loncornis (Deseado Early Oligocene of Rio Deseado, Argentina) - aramid?
- Riacama (Deseado Early Oligocene of Argentina)
- Smiliornis (Deseado Early Oligocene of Argentina)
- Pseudolarus (Deseado Early Oligocene - Miocene of Argentina) - gruiform?
- Gnotornis (Brule Late Oligocene of Shannon County, USA) - aramid?
- Anisolornis (Santa Cruz Middle Miocene of Karaihen, Argentina) - aramid?
- Alvarenga, Herculano M. F. & Höfling, Elizabeth (2003): Systematic revision of the Phorusrhacidae (Aves: Ralliformes). Papéis Avulsos de Zoologia 43(4): 55-91 PDF fulltext
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- Fain, M. G., & P. Houde (2007) Multilocus perspectives on the monophyly and phylogeny of the order Charadriiformes (Aves). BMC Evolutionary Biology, 7:35. PDF fulltext
- Fain, M.G., C. Krajewski, & P. Houde. (2007) Phylogeny of "core Gruiformes" (Aves: Grues) and resolution of the Limpkin-Sungrebe problem. Molecular Phylogenetics and Evolution 43: 515-529. PDF fulltext
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- Morgan-Richards M., Trewick S. A., Bartosch-Härlid A., Kardailsky O., Phillips M. J., McLenachan P. A., Penny D. (2008): Bird evolution: testing the Metaves clade with six new mitochondrial genomes. BMC Evol Biol. Jan 23;8:20. PDF fulltext
- Olson, S. L. (1985) The fossil record of birds. Avian biology (D. S. Farner and King, J. R. & K. C. Parkes, eds.) 8: 79-238, Academic Press, Orlando.
- Olson, S. L., and D. W. Steadman (1981): The relationships of the Pedionomidae (Aves: Charadriformes). Smithsonian Contrib. Zool. 337: 1-25.
- Paton, Tara A. & Baker, Allan J. (2006): Sequences from 14 mitochondrial genes provide a well-supported phylogeny of the Charadriiform birds congruent with the nuclear RAG-1 tree. Molecular Phylogenetics and Evolution 39(3): 657–667. doi:10.1016/j.ympev.2006.01.011 PMID 16531074 (HTML abstract)
- Sibley, Charles Gald & Ahlquist, Jon Edward (1990): Phylogeny and classification of birds. Yale University Press, New Haven, Conn.
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