Vertebrate paleontology

Integrating experimental studies of biomechanics with studies of fossil taxa can reveal the steps through which major transitions in morphology and function unfolded (Blob 2006; Carrano etal. 2006). I have used data from our bone loading experiments to develop a computational model of limb bone stresses through the evolution of upright posture in the therapsid ancestors of mammals (Blob 2001). Results showed that the use of a wide range of limb postures was possible for these taxa, indicating that this evolutionary transition may have involved a ‘generalist’ stage between more specialized extremes. I also examined the ontogenetic allometry of limb bone proportions in fossil therapsids to test correlations between the evolution of bone growth patterns and the evolution of endothermy in the ancestors of mammals (Blob 2006).

Other paleontological work has documented faunas and biases in the fossil record, This has included taphonomic studies of Cretaceous faunas in Montana, evaluating how preservation biases affect paleoecological comparisons (Blob and Fiorillo 1996; Blob 1997; Blob and Badgley 2007). These studies led to the discovery of a new species of fossil amphibian (Blob et al. 2001; Gardner et al. 2010).

Current directions

• Analyses of femoral loading in opossums have given insight into patterns of cross-sectional shape asymmetry through the evolution of the femur in fossil therapsids, and how those relate to evolutionary changes in limb posture and loading regime (Butcher et al. 2011; Gosnell et al. 2011).

• PhD graduate Sandy Kawano has compared skeletal loading between salamander forelimbs and mudskipper pectoral fins (Kawano and Blob 2013), forming a basis for a computational model of changes in bone stress that affected skeletal design through the fish-to-tetrapod transition in the fossil record.

• Collaboration with Chris Sidor (University of Washington), Adam Huttenlocker (University of Utah) and Christian Kammerer (Humboldt Museum, Berlin) is evaluating the tendency for size-related reduction in limb bone curvature among gorgonopsian and therocephalian lineages of therapsids.

Related Publications

Blob, R. W. 1997. Relative hydrodynamic dispersal potentials of soft-shelled turtle elements: implications for interpreting skeletal sorting in assemblages of non-mammalian terrestrial vertebrates. Palaios 12: 151-164. Available HERE (erratum)

Blob, R. W. 2001. Evolution of hindlimb posture in non-mammalian therapsids: biomechanical tests of paleontological hypotheses. Paleobiology 27: 14-38. 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 C. Badgley. 2007. Numerical methods for bonebed analysis. Chapter 6 in R. Rogers, D. Eberth, and A. Fiorillo (eds.), Bonebeds: Genesis, Analysis, and Paleoecological Significance, University of Chicago Press, pp. 333-396. Available HERE (more about this book)

Blob, R. W., M. T. Carrano, R. R. Rogers, C. A. Forster, and N. R. Espinoza. 2001. A new fossil frog from the Upper Cretaceous Judith River Formation of Montana. Journal of Vertebrate Paleontology 21: 190-194. Available HERE

Blob, R. W. and A. R. Fiorillo. 1996. The significance of vertebrate microfossil size and shape distributions for faunal abundance reconstructions: a Late Cretaceous example. Paleobiology 22: 422-435. Available HERE

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

Gardner, J. D., Z. Rocek, T. Prikryl, J. G. Eaton, R. W. Blob, J. T. Sankey. 2010. Comparative morphology of the ilium of anurans and urodeles (Lissamphibia) and a re-assessment of the anuran affinities of Nezpercius dodsoni Blob et al., 2001. Journal of Vertebrate Paleontology 30: 1684-1696. Available HERE

Gaudin, T. J., Carrano, M. T., Blob, R. W., Wible, J. R. 2006. Introduction (Chapter 1). 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. 1-17. Available HERE (more about this book)

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

Kawano, S. M., R. W. Blob. 2013. Propulsive forces of mudskipper fins and salamander limbs during terrestrial locomotion: implications for the invasion of land. Integrative and Comparative Biology 53:283-294. Available HERE