Photo: Jordi Muntaner. Question marks: Aina Bonner

Challenge 7

Today this Challenge is on osteology

Knowledge of bird anatomy was in vogue among ornithologists more than a century ago. It is not so much now. The skeletal system of birds is extremely informative about how they evolved and how they work. Personally, I love bones. In this blog I will sporadically present osteological challenges, which may help us understand a little more the uniqueness and diversity of birds.

Bird wings are a great evolutionary invention. They are supported by the skeleton of the forelimb, which in birds is usually composed of the following segments:

humerus

radius-ulna

carpometacarpus (+ two small carpal bones)

proximal phalanges

distal phalanx

The bones of the first two segments are homologous to those of our arms (humerus) and forearms (radius and ulna), while those of the last three segments are the bones of the hands and wrists. The “hand” bones of birds support the primary feathers (and alula), while the secondary feathers are supported by the forearm (ulna), and the tertiary feathers by the arm (humerus). In the vast majority of birds, the design of the wings means that the carpometacarpus (the longest bone in the “hand” of birds) is shorter than the humerus. However, some birds are “rare”: All members of two orders of birds have carpometacarpi longer than their humeri. Do you know what these birds are?