The incidence of pneumatization in avian long bones Tvas studied, by direct
observation, in a large sample of species. Only proximal bones (humerus an
d femur) presented pneumatization in the sample studied. The incidence obta
ined was related to the variation of the maximum cortical thickness and mec
hanical properties, such as bending strength and flexural Young's modulus.
Cortical thickness, bending strength and flexural Young's modulus were sign
ificantly lower in pneumatized bones than in marrow-filled bones. Furthernn
ore, some congruence was found between pneumarization and systematic groups
when compared. In this sense, Charadriformes was the only order studied wi
th total absence of long bone pneumatization. Results on cortical thickness
appear to be in agreement with modelling predictions previously macle and
with results obtained on other groups of filing vertebrates. The possible s
elective advantage of reduction in cortical thickness in relation to flying
is suggested. (C) 2000 The Linnean Society of London.