Incidence and mechanical significance of pneumatization in the long bones of birds

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.