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First published online March 21, 2005
Journal of Experimental Biology 208, 1309-1319 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01522

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Testing the hindlimb-strength hypothesis: non-aerial locomotion by Chiroptera is not constrained by the dimensions of the femur or tibia

Daniel K. Riskin^1,*, John E. A. Bertram² and John W. Hermanson¹

¹ Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
² Department of Cell Biology and Anatomy, Faculty of Medicine, University of Calgary, Calgary, AB T2N 4N1, Canada

View larger version (80K): [in a new window]   Fig. 1. Typical locomotory sequences for (A) P. parnellii, (B) D. rotundus and (C) D. youngi. Images are at 44 ms intervals. In those images for which only the hindlimbs are in contact with the left plate, the normal force for that plate is shown as a yellow arrow. The graph below each image shows the magnitude of the force on the left plate over the course of the image sequence. Open yellow circles indicate the timing of images with force vectors. Solid circles give the times of all other frames. Note that the magnitude of the force vector for both vampire species decreases gradually as the animal shifts its weight forward, but that the forces are highly variable for the poorly crawling bat, P. parnellii.

View larger version (14K): [in a new window]   Fig. 2. Magnitudes of hindlimb force in D. rotundus, D. youngi, and P. parnellii: (A) total force, calculated as the vector sum of forces in the x, y and z directions; (B) vertical component of peak force. Asterisk denotes significance at P<0.05.

View larger version (11K): [in a new window]   Fig. 3. Sine of angle between force vectors and the long axis of a tibia vs magnitude of peak force in P. parnellii trials, where peak force occurred as a single leg was in contact with the plate.

View larger version (13K): [in a new window]   Fig. 4. Log–log plots of length to diameter for bat (A) femora (B) and tibiae. Red circles denote vampire bats. Other bat species are black. Bold line represents best fit and grey lines indicate 95% confidence interval from least squares regression of non-vampire bat data only.

View larger version (9K): [in a new window]   Fig. 5. Relative hindlimb bone stresses for femora (A) and tibiae (B) across the range of body masses in this study. Red circles represent vampire bats (D. rotundus, D. youngi), black circles represent other species. According to the hindlimb-strength hypothesis, the non-vampires should have relative bone stress values greater than that of D. youngi tibiae (1.0).