Branta: Transactions of the Azov-Black Sea Ornithological Station, 112-125
Some cases of morphofunctional adaptations of the limb skeleton in birds
Y. O. Broshko
Bipedalism in birds has significant effect on their limb morphology that is very conservative. Overspecialization of limbs leads to more significant adaptations of the skeleton.
Read the paper in a PDF file
In this work, the limb bones of seven bird species were investigated. They are humerus, ulna, radius, femur, tibiotarsus and tarsometatarsus (Table 1). The following parameters were evaluated: bone mass (m, g), total bone length (l, mm), frontal (df, mm) and sagittal (ds, mm) diameters of the mid-shaft; parameters of cross-sectional geometry of the mid-shaft: cortical area (А, mm2), second moments of area (Imax, Imin, mm4), polar moment of area (J, mm4) (Table 2). The following indices were also calculated: ratio of mid-shaft diameters (df/ds), cross-sectional index (ik), and ratio of second moments of area (Imax/Imin) (Table 3). Cortical area, second moments of area and polar moment of intertia represent the bone resistance to the various mechanical loads: compression, bending and torsion, respectively. The cross-section shape of the mid-shaft is directly associated with these parameters. Interspecific allometry of bone characteristics was investigated as well (Table 4 and 5).
It was established that wing bones are mainly characterized by elliptical cross-section shape (Fig. 1). However, in representatives of the genus Anas this shape is circular. It is explained by significant torsional loads caused by the intensity of flight. The most typical cross-section shape of hindlimb bones (especially femur) is circular (Fig. 2). This indicates the predominance of torsional loads in hindlimbs, caused by the most types of terrestrial locomotion. Swimming is accompanied by a significant increase of bending loads in the sagittal plane thereby resulting in an elliptical cross-section shape of the Anas femur. However, the latter characteristic is not the single adaptation to swimming.
Mechanical characteristics increase more intensively to adapt bird limb bones to the growth of relative mechanical loads induced by increasing of their body mass. It is demonstrated by positive allometry of these characteristics (b > 0.67 – for cortical area, b > 1.33 – for second moments of area). Linear dimensions of bones are mainly isometric to the body mass. Thus, in bipedalism, limb bone properties undergo qualitative changes (increase in strength and resistance to loads) rather than quantitative ones (relative enlargement).
- Alexander, R. McN. (1983). Allometry of the leg bones of moas (Dinornithes) and other birds. J. Zool., 200, 215-231.
- Alexander, R. McN. (2004). Bipedal animals and their differences from humans. J. Anat., 204, 321-330.
- Biewener, A. A. (1982). Bone strength in small mammals and bipedal birds: do safety factors change with body size? J. Exp. Biol., 98, 289-301.
- Blob, R. W., & Biewener A. (2001). Mechanics of limb bone loading during terrestrial locomotion in the green iguana (Iguana iguana) and American alligator (Alligator mississippiensis). J. Exp. Biol., 204, 1099-1122.
- Bogdanovich, I. A. (1995). Morphoecological description of apparatus of terrestrial locomotion in Common Coot (Fulica atra). Kiev. (Preprint / NAS of Ukraine, Institute of Zoology; 95.01)] [In Russian]
- Bogdanovich, I. A. (2014). Morphoecological peculiarities of pelvis in several genera of rails with some notes on systematic position of the coot, Fulica atra (Rallidae, Gruiformes), Vestnik zoologii, 48 (3), 249-254.
- Bogdanovich, I. A., & Klykov V. I. (2011). Peculiarities of the cross-section shape geometry of limb long bones in birds. Vestnik Zoologii, 45 (3), 283-288. [In Russian]
- Cubo, J., & Casinos, A. (1994). Scaling of skeletal element mass in birds. Belg. J. Zool., 124, 127-137.
- Cubo, J., & Casinos, A. (1997). Flightlessness and long bone allometry in Palaeognathiformes and Sphenisciformes. Neth. J. Zool, 47, 209-226.
- Cubo, J., & Casinos, A. (1998). The variation of the cross-sectional shape in the long bones of birds and mammals. An. Sc. Natur. 36 (1), 51-62.
- Farke, A. A., & Alicea, J. (2009). Femoral strength and posture in terrestrial birds and non-avian theropods. Anat. Rec., 292, 1406-1411.
- Garcia, G. J. M., & Silva, J. K. L. da. (2006). Interspecific allometry of bone dimensions: A review of the theoretical models. Phys. Life Rev, 3, 188-209.
- Gould, S. J. (1966). Allometry and size in ontogeny and phylogeny. Biol. Rev. Cambridge Phill. Soc., 41(5), 87-640.
- Habib, M. (2010). The structural mechanics and evolution of aquaflying birds. Biol. J. Linn. Soc. 99, 687-698.
- Habib, M. B., & Ruff, C. B. (2008). The effects of locomotion of the structural characteristics of avian long bones. Zool. J. Linn. Soc., 153, 601-624.
- Hutchinson, J. R., & Allen, V. (2009). The evolutionary continuum of limb function from early theropods to birds. Naturwissenschaften, 96, 423-448.
- Klebanova, Ye. A., Polyakova R. S., & Sokolov A. S. (1971). Morphofunctional peculiarities of support and motion organs in lagomorphs. Transactions of Zoological Institute, 48, 121-151. [In Russian]
- Lieberman, D. E., Polk, J. D., & Demes, B. (2004). Predicting long bone loading from cross-sectional geometry. Am. J. Phys. Anthrop., 123, 156-171.
- Main, R. P., & Biewener, A. A. (2007). Skeletal strain patterns and growth in the emu hindlimb during ontogeny. J. Exp. Biol., 210, 2676-2690.
- Maloiy, G. M. O., Alexander, R. McN., Njau R., & Jayes, A. S. (1979). Allometry of the legs of running birds. J. Zool., Lond., 187, 161-167.
- Margerie, E. de. (2002). Laminar bone as an adaptation to torsional loads in flapping flight. J. Anat., 201, 521-526.
- McMahon, T. A. (1973). Size and shape in biology. Science, 179, 1201-1204.
- Melnik, K. P., & Klykov, V. I. (1991). Locomotor apparatus of mammals. Aspects of morphology and biomechanics of the skeleton. Kiev: Naukova Dumka [In Russian]
- Prange, H. D., Anderson J. F., & Rahn H. (1979). Scaling of skeletal mass to body mass in birds and mammals. Amer. Natur., 113 (1), 103-122.
- Schmidt-Nielsen K. (1987). Scaling: Why is animal size so important? Moscow: Mir. [In Russian]
- Simons, E. L. R., Hieronymus, T. L., & O’Connor, P. M. (2011). Cross sectional geometry of the forelimb skeleton and flight mode in Pelecaniformes birds. Journal of Morphology, 272, 958-971.