Santos, Michelly S. dos, Furo, Ivanete O, Tagliarini, Marcella M, Krestschmer, Rafael, O'Brien, Patricia C. M, Ferguson-Smith, Malcolm A, and Oliveira, Edivaldo Herculano Correa de
Universidade Federal do Par?. Instituto de Ci?ncias Biol?gicas. Programa de P?s-gradua??o em Gen?tica e Biologia Molecular. Bel?m, PA, Brasil. Universidade Federal do Par?. Instituto de Ci?ncias Biol?gicas. Programa de P?s-gradua??o em Gen?tica e Biologia Molecular. Bel?m, PA, Brasil. Universidade Federal do Par?. Instituto de Ci?ncias Biol?gicas. Programa de P?s-gradua??o em Gen?tica e Biologia Molecular. Bel?m, PA, Brasil. Universidade Federal do Rio Grande do Sul. Programa de P?s-gradua??o em Gen?tica e Biologia Molecular. Porto Alegre, RS, Brasil. University of Cambridge. Department of Veterinary Medicine. Cambridge, UK. University of Cambridge. Department of Veterinary Medicine. Cambridge, UK. Universidade Federal do Par?. Instituto de Ci?ncias Exatas e Naturais. Bel?m, PA, Brasil / Minist?rio da Sa?de. Secretaria de Vigil?ncia em Sa?de. Instituto Evandro Chagas. Ananindeua, PA, Brasil. The hoatzin (Opisthocomus hoazin M?ller, 1776) is a folivorous bird, endemic to the Amazonian region. It presents some unique characteristics, including wing claws and foregut fermentation, which make its phylogenetic relationship to other birds difficult to determine. There have been various attempts to place it among the Galliformes, Gruiformes, Musophagiformes, Cuculiformes, and Charadriiformes, but phylogenetic analyses always show low supporting values. Nowadays, the hoatzin is included in the monotypic order Opisthocomiformes, but the relationship of this order to other groups of birds is still unclear. Although its karyotype resembles the typical avian model, fissions of the syntenic groups corresponding to chicken chromosomes 1 and 2 and 2 fusions were found. The presence of 18S rDNA clusters in 2 pairs of microchromosomes is another derived character. Hence, different rearrangements were detected in the karyotype of the hoatzin, indicating it has been derived from the putative ancestral karyotype by the occurrence of fissions and fusions. However, as these rearrangements are not exclusive to O. hoazin, they do not clarify the phylogenetic position of this enigmatic species.