From Opus

Order: Struthioniformes

[edit] Description

Large, flightless birds without a keel on the sternum.

[edit] Taxonomy

Struthioniformes is an order in the class Aves. Struthioniformes as given here is based on Clements¹; however, a different treatment is quite often seen, according to which the below families are placed in four orders (Struthioniformes, Rheiformes, Casuariiformes, and Dinornithiformes). In this second treatment, the flightless birds as a group are called Ratites, and the underlying assumption is that flight has only been lost once, in the common ancestor for the group.

A recent study strongly proposes that both of the above treatments are wrong²: Instead, the tinamous should be inserted into the middle of the groups included here with the ostriches as the basal group. That will lead to a conclusion that either the tinamous regained the ability for flight from a flightless ancestor, or the ability to fly was lost independently in two or more lineages; the authors argue that the second interpretation is by far the most likely. Tinamous together with flightless birds (Struthioniformes as used here) have for a long time been seen as one fundamental group of birds, Palaeograthae; Neognathae contains the remainder of the living birds.

[edit] References

1. Clements, James F. 2007. The Clements Checklist of Birds of the World. 6th ed., with updates to October 2007. Ithaca: Cornell University Press. ISBN 9780801445019
2. Harshman et al. 2008. Phylogenomic evidence for multiple losses of flight in ratite birds. PNAS 105:13462-13467