Gruiformes

Lore & Background

Over the decades, many ornithologists suggested that members of the order were in fact more closely related to other groups. Olson and Steadman were first to correctly disband any of the traditional Gruiformes, recognizing that the Australian plains-wanderer was actually a member of the shorebirds based on skeletal characters. This was confirmed by DNA–DNA hybridization and subsequent genetic studies. Using 12S ribosomal DNA sequences, Houde et al. were the first to present molecular genetic evidence of gruiform polyphyly. 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. The suborder Grues includes rails, flufftails, finfoots, adzebills, trumpeters, limpkin, and cranes—these are the only true Gruiformes. The suborder Eurypygae includes the kagu and sunbittern, which are not even remotely related to Grues. Fain and Houde proposed that Neoaves are divisible into two clades, Metaves and Coronaves, though Metaves may be paraphyletic. Sunbittern, kagu, and mesites group within Metaves, while all other lineages of 'Gruiformes' group with waterbirds or landbirds within Coronaves. The kagu and sunbittern are one another's closest relatives, and the adzebills are in fact members of the Grues.

Reader's Guide

The Gruiformes order has been a taxonomic challenge for ornithologists, serving as a 'wastebasket' for birds that did not fit elsewhere. Its significance lies in how it illustrates the evolution of avian classification from morphology-based to molecular phylogenetics. The traditional grouping, established by Max Fürbringer, was gradually dismantled as skeletal and genetic evidence revealed that many supposed Gruiformes are unrelated. Olson and Steadman's removal of the plains-wanderer to Charadriiformes, and subsequent DNA studies showing five to seven unrelated clades, transformed understanding of bird relationships. The core Gruiformes (Grues) include cranes, rails, and their relatives, while the kagu and sunbittern form a separate lineage. This history underscores the importance of integrating multiple data sources—morphology, DNA hybridization, and multiple genetic loci—to resolve deep avian relationships. The ongoing debate about Metaves and Coronaves, and the role of mitochondrial DNA, shows that even with advanced techniques, some questions remain unsettled. The Gruiformes thus serve as a case study in the dynamic nature of biological classification.

Did You Know?

• Olson and Steadman were first to correctly disband any of the traditional Gruiformes, recognizing the Australian plains-wanderer as a shorebird.
• The kagu and sunbittern are one another's closest relatives, but are not even remotely related to core Gruiformes.
• The adzebills, once thought to be a distinct Gondwanan lineage with kagu and sunbittern, are in fact members of the Grues.