Jason Head

Assistant Professor

Ph.D., 2002, Southern Methodist University

Vertebrate paleontology, Ecosystem studies, Paleoclimatology

Contact Information

228 Bessey Hall

I am a vertebrate paleontologist and evolutionary morphologist with research programs devoted to studying the evolutionary history of Cenozoic reptiles and the role of developmental processes in the evolution of reptile body form based on anatomy.

My research on Cenozoic (and late Mesozoic) reptiles includes international field studies and combines new fossil discoveries with morphology of extant taxa and phylogenetic hypotheses based on molecular sequence data in order to reconstruct evolutionary histories including divergence timings, body size evolution, biogeographic patterns, and response to environmental histories. I conduct multinational field and laboratory studies of fossil herpetofaunas from the Latest Cretaceous and Cenozoic in order to determine the relationship between climate and evolution of extant clades during globally warm intervals, to constrain the minimum timing for the genetic divergences of modern species, and to provide new data for molecular and morphological phylogenetic analyses.

Continuing projects include climatic reconstruction using metabolic paleothermometry and reconstructing Neotropical biogeography. Body size in extant poikilotherms is ultimately regulated by ambient mean annual temperature for a given mass-specific metabolic rate. I derive the predictable relationship between body size and ambient temperature in extant reptiles to estimate paleotemperatures including the first terrestrial equatorial temperatures of the Paleogene based on the discovery of gigantism in Neotropical fossil herpetofaunas from Colombia. This research estimates paleotemperatures for latitudes and temporal intervals that previously lacked climatic proxy data, and provides a predictive model for poleward temperature gradient changes due to anthropogenic warming.

I am also studying Neotropical fossil herpetofaunas to include revised phylogenies of New World squamates incorporating new fossil discoveries from Colombia, Panama, and Southern North America, as well as tests of mitochondrial sequence divergence rates against new age estimates for dispersal across the Americas derived from recent fossil discoveries.

Selected Publications

  • Head, J. J., G. F. Gunnell, P. A. Holroyd, J. H. Hutchison, R. L. Ciochon, , 2013, Giant Lizards occupied herbivorous mammalian ecospace during the Paleogene greenhouse in Southeast Asia, Proceedings of the Royal Society of London, Series B, doi:10.1098/rspb.2013.0665.

  • Head, J. J., A. F. Rincon, C. Suarez, C. Montes, C. Jaramillo, 2012, Fossil evidence for earliest Neogene American faunal interchange: Boa (Serpentes, Boinae) from the early Miocene of Panama, Journal of Vertebrate Paleontology, 32, 1328-1334.

  • Lawing, A. M., J. J. Head, P. D. Polly, 2012, The ecology of morphology: the ecometrics of locomotion and macroenvironment in North American snakes, in Palaeontology in Ecology and Conservation (edited by J. Louys), Springer, New York, 117-146.

  • Parham, J. F, P. C. J. Donoghue, C. J. Bell, T. D. Calway, J. J. Head, P. A. Holroyd, J. G. Inoue, R. B. Irmis, W. G. Joyce, D. T. Ksepka, J. S. L. Patańe, N. D. Smith, J. E. Tarver, M. van Tuinen, Z, 2012, Best practices for applying paleontological data to molecular divergence dating analyses, Systematic Biology, 61, 346-359.

  • Müller, J., C. Hipsley, J. J. Head, N. Kardjilov, A. Hilger, M. Wuttke, and R. R. Reisz, 2011, Limbed lizard from the Eocene of Germany reveals amphisbaenian origins, Nature, 473, 364-367.

  • Sanders, K. L., Mumpuni, A. Hamidy, J. J. Head, and D. J. Gower, 2010, Phylogeny and divergence times of filesnakes (Acrochordus): Inferences from morphology, fossils and three molecular loci, Molecular Phylogenetics and Evolution, 56, 857-867.

  • Müller, J., T. Scheyer, J.J. Head, P.M. Barrett, P. Ericson, D. Pol, M. R. Sanchéz-Villagra, 2010, The evolution of vertebral numbers in recent and fossil amniotes: The roles of homeotic effects and somitogenesis, Proceedings of the National Academy of Sciences of the United States of America, 107, 2118-2123.

  • Head, J. J., J. I. Bloch, A. K. Hastings, J. R. Bourque, E. A. Cadena, F. A. Herrera, P. D. Polly, C. A. Jaramillo, 2009, Communications Arising: Recalibrating the snake palaeothermometer, Reply, Nature, 460, doi:10.1038/nature08225.

  • Head, J. J., P. M. Barrett, E. J. Rayfield, 2009, Neurocranial osteology and systematic relationships of Varanus (Megalania) prisca Owen (Squamata, Varanidae), Zoological Journal of the Linnaean Society of London, 155, 445-457.

  • Head, J. J., J. I. Bloch, A. K. Hastings, J. R. Bourque, E. A. Cadena, F. A. Herrera, P. D. Polly, C. A. Jaramillo, 2009, Giant boid snake from the Paleocene neotropics reveals hotter past equatorial temperatures, Nature, 457, 715-717.