Xenicibis the club - winged, flightless, ibis

[Jason Brougham <jaseb@amnh.org>]

The bizarre wing of the Jamaican flightless ibis Xenicibis xympithecus: a 
unique vertebrate adaptation
Nicholas R. Longrich and Storrs L. Olson
Proceedings of the Royal Society B. published online 5 January 2011 doi: 
10.1098/rspb.2010.2117
http://rspb.royalsocietypublishing.org/content/early/2011/01/03/rspb.2010.2117.full.pdf

Birds have frequently evolved to exploit insular environments by becoming 
adapted to a terrestrial lifestyle and losing the ability to fly, usually via 
reducing the wings and pectoral girdle. The enigmatic flightless ibis Xenicibis 
xympithecus(Threskiornithidae) from the Quaternary of Jamaica provides a rare 
example of flight loss in ibises. We report on previously undescribed fossils 
of Xenicibis, and show that the wing differed radically from that of all other 
birds, flightless or volant. The metacarpus is elongate, grotesquely inflated 
and has extremely thick walls; phalanges are short and block-like; the radius 
is distally expanded; and the humerus is elongate. The furcula, coracoid and 
sternum are all well developed. We propose that the elongate forelimb and 
massive hand functioned in combat as a jointed club or flail. This hypothesis 
is supported by the morphology of the carpometacarpus, by features permitting 
rapid extension of the wing and by the presence of fractures in wing bones. 
Although other birds use the wings as weapons, none resemble Xenicibis, which 
represents a unique and extraordinary morphological solution to this functional 
problem. Xenicibisstrikingly illustrates how similar selective pressures, 
acting on a similar starting point, can result in novel outcomes.

Jason Brougham
Senior Principal Preparator
American Museum of Natural History
jaseb@amnh.org
(212) 496 3544