Bock, Walter J. Department of Biological Sciences, Columbia University, New York, New York.
- Related Primary Literature
- Additional Reading
A small order of birds containing a single family, the Opisthocomidae. The order Opisthocomiformes contains one species, Opisthocomus hoazin, which is commonly known as the hoatzin (see illustration). It is restricted to South America and has been frequently included in the Galliformes as a suborder; however, little evidence supports this conclusion. More recently, some researchers claimed that it was a typical member of the Cuculidae, the cuckoos, based only on evidence from deoxyribonucleic acid (DNA) hybridization studies. However, important differences in the morphology of the perching foot argue strongly against the inclusion of the hoatzin in Cuculidae. The hoatzin has an anisodactyl perching foot with three anterior toes and a well-developed hallux (first toe); this arrangement is completely different from the zygodactyl perching foot of the cuckoos (with the second and third toes anterior, and the fourth toe and hallux posterior). Selective demands for perching could not have resulted in the evolution of the anisodactyl foot of the hoatzin from the zygodactyl foot of the cuckoos. In the absence of definite evidence of its relationship to other avian orders, the Opisthocomiformes is best considered as a distinct order that evolved in South America since its isolation from the rest of Gondwana sometime in the late Mesozoic. See also: Cuculiformes; Galliformes
The content above is only an excerpt.
for your institution. Subscribe
To learn more about subscribing to AccessScience, or to request a no-risk trial of this award-winning scientific reference for your institution, fill in your information and a member of our Sales Team will contact you as soon as possible.
to your librarian. Recommend
Let your librarian know about the award-winning gateway to the most trustworthy and accurate scientific information.
AccessScience provides the most accurate and trustworthy scientific information available.
Recognized as an award-winning gateway to scientific knowledge, AccessScience is an amazing online resource that contains high-quality reference material written specifically for students. Contributors include more than 9000 highly qualified scientists and 43 Nobel Prize winners.
MORE THAN 8700 articles covering all major scientific disciplines and encompassing the McGraw-Hill Encyclopedia of Science & Technology and McGraw-Hill Yearbook of Science & Technology
115,000-PLUS definitions from the McGraw-Hill Dictionary of Scientific and Technical Terms
3000 biographies of notable scientific figures
MORE THAN 19,000 downloadable images and animations illustrating key topics
ENGAGING VIDEOS highlighting the life and work of award-winning scientists
SUGGESTIONS FOR FURTHER STUDY and additional readings to guide students to deeper understanding and research
LINKS TO CITABLE LITERATURE help students expand their knowledge using primary sources of information