FLIGHTLESSNESS AND LONG-BONE ALLOMETRY IN PALAEOGNATHIFORMES AND SPHENISCIFORMES

Palaeognathiformes and Sphenisciformes are the only two major taxa tha t have lost the capacity for flying. Nevertheless, the consequences of this flightlessness are completely different. While Palaeognathiforme s are all running birds, Sphenisciformes are adapted to swimming. To s tudy the morphology of leg and wing bones, length, sagittal and transv erse diameters and second moment of area of humerus, ulna, radius, fem ur, tibiotarsus and tarsometatarsus were measured. Thirty-three specim ens from fourteen species of Palaeognathiformes and eleven specimens f rom seven species of Sphenisciformes were studied. Several non-flying species from other avian orders were also considered. Regressions of a ll these parameters were calculated with body mass as the independent variable. For each bone, the ratio sagittal diameter/transverse diamet er was also calculated. Most of the correlations are significantly dif ferent from the isometric condition. From a mechanical point of view, the most interesting result is that the second moment of area of the l eg long bones always scales with strong positive allometry, whereas in the case of the wing long bones, the scaling shows high negative allo metry. Biometrically, Sphenisciformes display a constant wing long bon e morphology, with transverse diameters much larger than sagittal. In contrast, Palaeognathiformes present a highly variable morphology of t he wing bones, affecting length and diameters.