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Vertebrate skeletons serve diverse functions, ranging from supporting the body, to protecting internal organs, to serving as weapons in agonistic encounters. The ability of a skeletal element to perform these functions is affected by its size, its shape, and the mechanical properties of its bone material. How have evolutionary changes in each of these variables contributed to the evolution of functional diversity in the skeleton?
We have examined the allometry and mechanical properties of amphibian and reptilian limb bones (Blob and Biewener 1999; Blob 2000; Butcher and Blob 2008; Wilson et al. 2009; Sheffield and Blob 2011; Sheffield et al. 2011; Butcher et al. 2011), and performed mechanical tests on antler from different deer species (Blob and LaBarbera 2001; Blob and Snelgrove 2006; Shah et al. 2008) to evaluate variation in the properties of bones in a phylogenetic context. We found significant differences in bone mechanical properties among closely related species, indicating that bone material, as well as size and shape, can change through evolution to help meet the diverse demands that animals place on their skeletons. We have also extended our applications of phylogenetic comparative methods to evaluate the evolution of sexual size dimorphism in turtle shells (Gosnell et al. 2009).
This material is based upon work supported by the National Science Foundation under Grant No. 0517340. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation.
Current directions
• Comparisons of in vivo bone strains from the forelimbs and hindlimbs of amphibians and reptiles to test Alexander’s "Mixed Chain Hypothesis,” which predicts that structures within the body should have similar safety factors unless loads are highly variable (Blob et al., 2014).
• PhD student Vanessa Young is leading comparisons of limb bone loading between swimming and walking in turtles to evaluate implications for the evolution of limb bone flattening in secondarily aquatic vertebrates (Young and Blob 2015).
Related Publications
Blob, R. W. 2000. Interspecific scaling of the hind limb skeleton in lizards, crocodilians, felids and canids: does limb bone shape correlate with limb posture? Journal of Zoology 250: 507-531. Available HERE
Blob, R. W. 2006. Scaling of the hindlimb skeleton in cynognathian cynodonts: implications for ontogeny and thermoregulation (Chapter 13). In M. T. Carrano, T. J. Gaudin, R. W. Blob, and J. R. Wible (eds.), Amniote Paleobiology: Perspectives on the Evolution of Mammals, Birds, and Reptiles, University of Chicago Press, pp. 410-431. Available HERE (more about this book)
Blob, R. W. and A. A. Biewener. 1999. In vivo locomotor strain in the hind limb bones of Alligator mississipiensis and Iguana iguana: implications for the evolution of limb bone safety factor and non-sprawling limb posture. Journal of Experimental Biology 202: 1023-1046. Available HERE
Blob, R. W. and M. LaBarbera. 2001. Correlates of variation in deer antler stiffness: age, mineral content, intra-antler location, habitat, and phylogeny. Biological Journal of the Linnean Society 74: 113-120. Available HERE
Blob, R. W., and J. M. Snelgrove. 2006. Antler stiffness in moose (Alces alces): correlated evolution of bone function and material properties? Journal of Morphology 267: 1075-1086. Available HERE
Blob, R. W., N. R. Espinoza, M. T. Butcher, A. H. Lee, A. R. D’Amico, F. Baig, K. M. Sheffield. 2014. Diversity of limb bone safety factors for locomotion in terrestrial vertebrates: evolution and mixed chains. Integrative and Comparative Biology 54:1058-1071. Available HERE
Butcher, M. T. and Blob, R. W. 2008. Mechanics of limb bone loading during terrestrial locomotion in river cooter turtles (Pseudemys concinna). Journal of Experimental Biology 211: 1187-1202. Available HERE (corregendium)
Butcher, M. T., B. J. White, N. B. Hudzik, W. C. Gosnell, J. H. A. Parrish, R. W. Blob. 2011. In vivo strains in the femur of the Virginia opossum (Didelphis virginiana) during terrestrial locomotion: testing hypotheses of evolutionary shifts in mammalian bone loading and design. Journal of Experimental Biology 214: 2631-2640. Available HERE
Copploe, J. V. II., R. W. Blob, J. H. A. Parrish, M. T. Butcher. 2015. In vivo strains in the femur of the nine-banded armadillo (Dasypus novemcinctus). Journal of Morphology 276:889-899. Available HERE
Gosnell, W. C., M. T. Butcher, T. Maie, R. W. Blob. 2011. Femoral loading mechanics in the Virginia opossum (Didelphis virginiana): torsion and mediolateral bending in mammalian locomotion. Journal of Experimental Biology 214: 3455-3466. Available HERE
Gosnell, J. S., G. Rivera, R. W. Blob. 2009. A phylogenetic analysis of sexual size dimorphism in turtles. Herpetologica 65: 70-81. Available HERE
Shah, S. R., J. D. DesJardins, and R. W. Blob. 2008. Antler stiffness in caribou (Rangifer tarandus): testing variation in bone material properties between males and females. Zoology (Jena) 111: 476-482. Available HERE
Sheffield, K. M., R. W. Blob. 2011. Loading mechanics of the femur in tiger salamanders (Ambystoma tigrinum) during terrestrial locomotion. Journal of Experimental Biology 214: 2603-2615. Available HERE
Sheffield, K. M., M. T. Butcher, S. K. Shugart, J. C. Gander, R. W. Blob. 2011. Locomotor loading mechanics in the hindlimbs of tegu lizards (Tupinambis merianae): comparative and evolutionary implications. Journal of Experimental Biology 214: 2616-2630. Available HERE
Wilson, M. P., N. R. Espinoza, S. R. Shah, R. W. Blob. 2009. Mechanical properties of the hindlimb bones of bullfrogs and cane toads in bending and torsion. The Anatomical Record 292: 935-944. Available HERE
Young, V. K H., R. W. Blob. 2015. Limb-bone loading in swimming turtles: Changes in loading facilitate transitions from tubular to flipper-shaped limbs during aquatic invasions. Biology Letters 11, DOI: 10.1098/rsbl.2015.0110. (write for PDF)
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