page_title: Hoatzin
section_title: History of the debate
hierarchical_section_title: Hoatzin / Taxonomy, systematics and evolution / History of the debate
caption_attribution_description: English: Hoatzin on oxbow lake near Refugio Amazonas, Madre de Dios Region, Peru.
context_page_description: The hoatzin, also known as the reptile bird, skunk bird, stinkbird, or Canje pheasant, is a species of tropical bird found in swamps, riparian forests, and mangroves of the Amazon and the Orinoco basins in South America. It is notable for having chicks that have claws on two of their wing digits.
  It is the only member of the genus Opisthocomus. This is the only extant genus in the family Opisthocomidae. The taxonomic position of this family has been greatly debated by specialists, and is still far from clear.
context_section_description: Historical placement as gamebirds is based mainly on phenetic considerations of external morphology, which are considered unreliable and generally dismissed today; the gamebirds together with the waterfowl are classified as Galloanserae whereas the hoatzin are not. However, cuckoos have zygodactyl feet (two toes forward, two backward) and turacos are semi-zygodactylous, whereas the hoatzin has the more typical anisodactyl foot with three toes forward, one backwards. The evolution of avian dactyly, on the other hand, is not entirely resolved to satisfaction.
  Sibley and Ahlquist in 1990 considered the hoatzin likely to be a basal cuckoo based on DNA-DNA hybridization. Avise et al. in 1994 found mtDNA cytochrome b sequence data to agree with Sibley and Ahlquist's previous treatment. Subsequently, Hughes and Baker in 1999 proclaimed to have "resolved" the relationships of the hoatzin to be with turacos, based on their own analysis of 6 sets of mtDNA and one of nDNA sequences.
   
  Using mitochondrial and nuclear DNA sequences of increased length, Sorenson et al. in 2003 noted that all three previous DNA studies were apparently flawed due to errors in methodology, small sample size, and sequencing errors; their study strongly suggested against a close relationship between the hoatzin and cuckoos or turacos. It was not possible, though, to reliably determine the hoatzin's closest living relatives. Even though it tended to group with doves, this was not at all well-supported, with little more than 10% likelihood at best that such an arrangement was accurate according to Sorenson et al.s analysis.
  Fain and Houde in 2004 proposed a dichotomy in the Neoaves (neognaths excluding fowl) based on β-fibrinogen intron 7 (FGB-int7) sequences. In their suggested phylogeny, the hoatzin was a basal member of the Metaves, a proposed clade that would include many other historically problematic bird families, such as flamingos, grebes, tropicbirds, sandgrouse and mesites. While the doves did also group with the "Metaves", no close relationship between these and the hoatzin within Metaves was recovered.
  While the other major neoavian lineage, Coronaves, largely agreed in its internal phylogeny with what is currently emerging as consensus, the interrelationships of the "Metaves" were not resolvable. Nor do supposed metavian groupings like flamingos and nightjars or tropicbirds and hummingbirds seem to have a factual basis rather than being artifactually grouped based on molecular homoplasies or lack of informative characters within the group, as Fain and Houde originally suggested; Metaves instead may be a "wastebasket taxon".
  It seems probable that the taxa included in the Metaves by Fain and Houde contain some good clades, such as Caprimulgiformes, the Mirandornithes, or the Apodiformes. Considering that some "odd Gruiformes" which might be each other's closest living relatives make up most of the remaining Metaves, the doves, the hoatzin, and sandgrouse would remain as "Metaves incerta sedis" (Metaves with uncertain placement). This would seem to suggest that the hoatzin is at least more closely related to doves than to many of the other purported 'coronavian' families that previously have been suggested.  Subsequent multigene studies of Ericson et al. 2006 and of Hackett et al. 2008 corroborated the Metaves clades, dependent on the inclusion of one and two genes respectively, but the latter did not recover the hoatzin with Metaves.
  More recently, Houde embarked on sequencing the entire genome of the hoatzin.  As of 2011, it was reported that more than 1.4 billion base pairs of hoatzin DNA had been sequenced, roughly equal to its entire haploid genome, but that only about 2.4% of its genome had yet been assembled. Completion of this project would be welcomed for more reasons than resolution of hoatzin relationships.  Out of the diverse Class Aves, the genomes of no more than 4 species of birds including of the waterfowl/fowl and songbirds have been sequenced. Moreover, much might be learned by coordinating these efforts with that of the metageno
caption: Group of five in Peru
exif: {"Image Make": "NIKON CORPORATION", "Image Model": "NIKON D300", "Image Orientation": "0", "Image XResolution": "300", "Image YResolution": "300", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Picasa 3.0", "Image DateTime": "2009:09:01 14:49:11", "Image Artist": "", "Image YCbCrPositioning": "Co-sited", "Image Copyright": "", "Image ExifOffset": "330", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "1122", "Thumbnail JPEGInterchangeFormatLength": "8508", "EXIF ExposureTime": "1/80", "EXIF FNumber": "28/5", "EXIF ExposureProgram": "Program Normal", "EXIF ISOSpeedRatings": "800", "EXIF ExifVersion": "0221", "EXIF DateTimeOriginal": "2009:09:01 14:49:11", "EXIF DateTimeDigitized": "2009:09:01 14:49:11", "EXIF ComponentsConfiguration": "YCbCr", "EXIF CompressedBitsPerPixel": "4", "EXIF ExposureBiasValue": "-2/3", "EXIF MaxApertureValue": "5", "EXIF MeteringMode": "CenterWeightedAverage", "EXIF LightSource": "Unknown", "EXIF Flash": "Flash did not fire", "EXIF FocalLength": "200", "EXIF SubSecTime": "25", "EXIF SubSecTimeOriginal": "25", "EXIF SubSecTimeDigitized": "25", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "Uncalibrated", "EXIF ExifImageWidth": "1795", "EXIF ExifImageLength": "1284", "Interoperability InteroperabilityIndex": "R98", "Interoperability InteroperabilityVersion": "[48, 49, 48, 48]", "EXIF InteroperabilityOffset": "998", "EXIF SensingMethod": "One-chip color area", "EXIF FileSource": "Digital Camera", "EXIF SceneType": "Directly Photographed", "EXIF CVAPattern": "[0, 2, 0, 2, 0, 1, 1, 2]", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Manual", "EXIF DigitalZoomRatio": "1", "EXIF FocalLengthIn35mmFilm": "300", "EXIF SceneCaptureType": "Standard", "EXIF GainControl": "Low gain up", "EXIF Contrast": "Normal", "EXIF Saturation": "Normal", "EXIF Sharpness": "Hard", "EXIF SubjectDistanceRange": "0", "EXIF ImageUniqueID": "f9ff5146287cc3afa4ce84bdaa736cad"}