Body Size and Extinction Risk in Terrestrial Mammals Above the Species Level

Susumu Tomiya
The American Naturalist
Vol. 182, No. 6 (December 2013), pp. E196-E214
DOI: 10.1086/673489
Stable URL:
Page Count: 19
  • Download PDF
  • Cite this Item

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:


Log in to your personal account or through your institution.

Body Size and Extinction Risk in Terrestrial Mammals Above the Species Level
We're having trouble loading this content. Download PDF instead.


AbstractMammalian body mass strongly correlates with life history and population properties at the scale of mouse to elephant. Large body size is thus often associated with elevated extinction risk. I examined the North American fossil record (28–1 million years ago) of 276 terrestrial genera to uncover the relationship between body size and extinction probability above the species level. Phylogenetic comparative analysis revealed no correlation between sampling-adjusted durations and body masses ranging 7 orders of magnitude, an observation that was corroborated by survival analysis. Most of the ecological and temporal groups within the data set showed the same lack of relationship. Size-biased generic extinctions do not constitute a general feature of the Holarctic mammalian faunas in the Neogene. Rather, accelerated loss of large mammals occurred during intervals that experienced combinations of regional aridification and increased biomic heterogeneity within continents. The latter phenomenon is consistent with the macroecological prediction that large geographic ranges are critical to the survival of large mammals in evolutionary time. The frequent lack of size selectivity in generic extinctions can be reconciled with size-biased species loss if extinctions of large and small mammals at the species level are often driven by ecological perturbations of different spatial and temporal scales, while those at the genus level are more synchronized in time as a result of fundamental, multiscale environmental shifts.

Notes and References

This item contains 121 references.

Literature Cited
  • ['Agosta, S. J., and J. Bernardo. 2013. New macroecological insights into functional constraints on mammalian geographical range size. Proceedings of the Royal Society B: Biological Sciences 280:20130140, doi:10.1098/rspb.2013.0140.']
  • ['Alroy, J. 1996. Constant extinction, constrained diversification, and uncoordinated stasis in North American mammals. Palaeogeography, Palaeoclimatology, Palaeoecology 127:285–311.']
  • ['———. 2009. Speciation and extinction in the fossil record of North American mammals. Pages 301–333 in R. K. Butlin, J. R. Bridle, and D. Schluter, eds. Speciation and patterns of diversity. Cambridge University Press, Cambridge.']
  • ['Badgley, C., and J. A. Finarelli. 2013. Diversity dynamics of mammals in relation to tectonic and climatic history: comparison of three Neogene records from North America. Paleobiology 39:373–399.']
  • ['Barnosky, A. D., and M. A. Carrasco. 2002. Effects of Oligo-Miocene global climate changes on mammalian species richness in the northwestern quarter of the USA. Evolutionary Ecology Research 4:811–841.']
  • ['Barnosky, A. D., N. Matzke, S. Tomiya, G. O. U. Wogan, B. Swartz, T. B. Quental, C. Marshall, et al. 2011. Has the Earth’s sixth mass extinction already arrived? Nature 471:51–57.']
  • ['Bininda-Emonds, O. R. P., M. Cardillo, K. E. Jones, R. D. E. MacPhee, R. M. D. Beck, R. Grenyer, S. A. Price, R. A. Vos, J. L. Gittleman, and A. Purvis. 2007. The delayed rise of present-day mammals. Nature 446:507–512.']
  • ['———. 2008. Corrigendum: the delayed rise of present-day mammals (Nature 446:507–512, 2007). Nature 456:274.']
  • ['Blois, J. L., J. L. McGuire, and E. A. Hadly. 2010. Small mammal diversity loss in response to late-Pleistocene climate change. Nature 465:771–774.']
  • ['Blomberg, S. P., T. Garland Jr., and A. R. Ives. 2003. Testing for phylogenetic signal in comparative data: behavioral traits are more labile. Evolution 57:717–745.']
  • ['Brown, J. H., and B. A. Maurer. 1989. Macroecology: the division of food and space among species on continents. Science 243:1145–1150.']
  • ['Brown, J. H., and P. F. Nicoletto. 1991. Spatial scaling of species composition: body masses of North American land mammals. American Naturalist 138:1478–1512.']
  • ['Burnham, K. P., and D. R. Anderson. 2002. Model selection and inference: a practical information-theoretic approach. 2nd ed. Springer, New York.']
  • ['Calede, J. J. M., S. B. S. Hopkins, and E. B. Davis. 2011. Turnover in burrowing rodents: the roles of competition and habitat change. Palaeogeography, Palaeoclimatology, Palaeoecology 311:242–255.']
  • ['Cardillo, M., G. M. Mace, J. L. Gittleman, K. E. Jones, J. Bielby, and A. Purvis. 2008. The predictability of extinction: biological and external correlates of decline in mammals. Proceedings of the Royal Society B: Biological Sciences 275:1441–1448.']
  • ['Cardillo, M., G. M. Mace, K. E. Jones, J. Bielby, O. R. P. Bininda-Emonds, W. Sechrest, C. D. L. Orme, and A. Purvis. 2005. Multiple causes of high extinction risk in large mammal species. Science 309:1239–1241.']
  • ['Carotenuto, F., C. Barbera, and P. Raia. 2010. Occupancy, range size, and phylogeny in Eurasian Pliocene to Recent large mammals. Paleobiology 36:399–414.']
  • ['Carrasco, M. A., B. P. Kraatz, E. B. Davis, and A. D. Barnosky. 2005. Miocene mammal mapping project (MIOMAP), University of California Museum of Paleontology,, data set downloaded on March 6, 2012.']
  • ['Casanovas-Vilar, I., I. García-Paredes, D. M. Alba, L. W. van den Hoek Ostende, and S. Moyà-Solà. 2010. The European far west: Miocene mammal isolation, diversity and turnover in the Iberian Peninsula. Journal of Biogeography 37:1079–1093.']
  • ['Clauset, A., and D. H. Erwin. 2008. The evolution and distribution of species body size. Science 321:399–401.']
  • ['Costeur, L., and S. Legendre. 2008. Spatial and temporal variation in European Neogene large mammals diversity. Palaeogeography, Palaeoclimatology, Palaeoecology 261:127–144.']
  • ['Costeur, L., S. Legendre, and G. Escarguel. 2004. European large mammals palaeobiogeography and biodiversity during the Neogene: palaeogeographic and climatic impacts. Revue de Paléobiologie 9(vol. spéc.):99–109.']
  • ['Creighton, G. K. 1980. Static allometry of mammalian teeth and the correlation of tooth size and body size in contemporary mammals. Journal of Zoology 191:435–443.']
  • ['Damuth, J. 1991. Of size and abundance. Nature 351:268–269.']
  • ['Damuth, J., and C. M. Janis. 2011. On the relationship between hypsodonty and feeding ecology in ungulate mammals, and its utility in palaeoecology. Biological Reviews 86:733–758.']
  • ['Davidson, A. D., M. J. Hamilton, A. G. Boyer, J. H. Brown, and G. Ceballos. 2009. Multiple ecological pathways to extinction in mammals. Proceedings of the National Academy of Sciences of the USA 106:10702–10705.']
  • ['Davis, E. B. 2005. Mammalian beta diversity in the Great Basin, western USA: palaeontological data suggest deep origin of modern macroecological structure. Global Ecology and Biogeography 14:479–490.']
  • ['Dawson, M. R. 1999. Bering down: Miocene dispersals of land mammals between North America and Europe. Pages 473–483 in G. E. Rössner and K. Heissig, eds. The Miocene land mammals of Europe. Pfeil, Munich.']
  • ['de Queiroz, K. 2007. Species concepts and species delimitation. Systematic Biology 56:879–886.']
  • ['Diniz-Filho, J. A. F., P. Carvalho, L. M. Bini, and N. M. Tôrres. 2005. Macroecology, geographic range size-body size relationship and minimum viable population analysis for New World Carnivora. Acta Oecologica 27:25–30.']
  • ['Efron, B. 1981. Nonparametric standard errors and confidence intervals. Canadian Journal of Statistics 9:139–158.']
  • ['Eisenberg, J. F. 1981. The mammalian radiations: an analysis of trends in evolution, adaptation, and behavior. University of Chicago Press, Chicago.']
  • ['Eronen, J. T., M. M. Ataabadi, A. Micheels, A. Karme, R. L. Bernor, and M. Fortelius. 2009. Distribution history and climatic controls of the late Miocene Pikermian chronofauna. Proceedings of the National Academy of Sciences of the USA 106:11867–11871.']
  • ['Eronen, J. T., M. Fortelius, A. Micheels, F. T. Portmann, K. Puolamäki, and C. Janis. 2012. Neogene aridification of the Northern Hemisphere. Geology 40:823–826.']
  • ['Eronen, J. T., K. Puolamäki, K. Lintulaakso, J. Damuth, C. Janis, and M. Fortelius. 2010. Precipitation and large herbivorous mammals II: application to fossil data. Evolutionary Ecology Research 12:235–248.']
  • ['Erwin, D. H. 2008. Extinction as the loss of evolutionary history. Proceedings of the National Academy of Sciences of the USA 105:11520–11527.']
  • ['Flynn, L. J., J. C. Barry, M. E. Morgan, D. Pilbeam, L. L. Jacobs, and E. H. Lindsay. 1995. Neogene Siwalik mammalian lineages: species longevities, rates of change, and modes of speciation. Palaeogeography, Palaeoclimatology, Palaeoecology 115:249–264.']
  • ['Fortelius, M. 2012. NOW: New and Old Worlds Database of Fossil Mammals, University of Helsinki. Data set downloaded on December 2, 2012.']
  • ['Fortelius, M., L. Werdelin, P. Andrews, R. L. Bernor, A. Gentry, L. Humphrey, H. W. Mittmann, and S. Viranta. 1996. Provinciality, diversity, turnover, and paleoecology in land mammal faunas of the later Miocene of western Eurasia. Pages 414–448 in R. L. Bernor, V. Fahlbusch, and H. W. Mittmann, eds. The evolution of western Eurasian Neogene mammal faunas. Columbia University Press, New York.']
  • ['Freckleton, R. P., P. H. Harvey, and M. Pagel. 2002. Phylogenetic analysis and comparative data: a test and review of evidence. American Naturalist 160:712–726.']
  • ['Fritz, S. A., O. R. P. Bininda-Emonds, and A. Purvis. 2009. Geographical variation in predictors of mammalian extinction risk: big is bad, but only in the tropics. Ecology Letters 12:538–549.']
  • ['Gardezi, T., and J. da Silva. 1999. Diversity in relation to body size in mammals: a comparative study. American Naturalist 153:110–123.']
  • ['Gaston, K. J., and T. M. Blackburn. 1996. Conservation implications of geographical range size-body size relationships. Conservation Biology 10:638–646.']
  • ['Gill, J. L., J. W. Williams, S. T. Jackson, K. B. Lininger, and G. S. Robinson. 2009. Pleistocene megafaunal collapse, novel plant communities, and enhanced fire regimes in North America. Science 326:1100–1103.']
  • ['Graham, R. W., and E. L. Lundelius. 2010. FAUNMAP II: new data for North America with a temporal extension for the Blancan, Irvingtonian and early Rancholabrean. Data set downloaded on March 6, 2012.']
  • ['Hadly, E. A., P. A. Spaeth, and C. Li. 2009. Niche conservatism above the species level. Proceedings of the National Academy of Sciences of the USA 106:19707–19714.']
  • ['Harrell, F. E. 2012. Regression modeling strategies (package “rms”). Version 3.5-0.']
  • ['Hernández Fernández, M., and E. S. Vrba. 2005. Body size, biomic specialization and range size of African large mammals. Journal of Biogeography 32:1243–1256.']
  • ['Hopkins, S. B. S. 2007. Causes of lineage decline in the Aplodontidae: testing for the influence of physical and biological change. Palaeogeography, Palaeoclimatology, Palaeoecology 246:331–353.']
  • ['Hulbert, J., R. C. 1993. Taxonomic evolution in North American Neogene horses (subfamily Equinae): the rise and fall of an adaptive radiation. Paleobiology 19:216–234.']
  • ['Isaac, N. J. B., and G. Cowlishaw. 2004. How species respond to multiple extinction threats. Proceedings of the Royal Society B: Biological Sciences 271:1135–1141.']
  • ['Isaac, N. J. B., K. E. Jones, J. L. Gittleman, and A. Purvis. 2005. Correlates of species richness in mammals: body size, life history, and ecology. American Naturalist 165:600–607.']
  • ['IUCN (International Union for Conservation of Nature). 2012. IUCN Red List of Threatened Species. Version 2012.2. Data set downloaded on January, 25, 2013.']
  • ['Janis, C. M. 1993. Tertiary mammal evolution in the context of changing climates, vegetation, and tectonic events. Annual Review of Ecology and Systematics 24:467–500.']
  • ['Janis, C. M., J. Damuth, and J. M. Theodor. 2002. The origins and evolution of the North American grassland biome: the story from the hoofed mammals. Palaeogeography, Palaeoclimatology, Palaeoecology 177:183–198.']
  • ['Janis, C. M., G. F. Gunnell, and M. D. Uhen. 2008. Evolution of Tertiary mammals of North America. Vol. 2. Small mammals, xenarthrans, and marine mammals. Cambridge University Press, Cambridge.']
  • ['Janis, C. M., K. M. Scott, and L. L. Jacobs. 1998. Evolution of Tertiary mammals of North America. Vol. 1. Terrestrial carnivores, ungulates, and ungulatelike mammals. Cambridge University Press, Cambridge.']
  • ['Jernvall, J., and M. Fortelius. 2004. Maintenance of trophic structure in fossil mammal communities: site occupancy and taxon resilience. American Naturalist 164:614–624.']
  • ['Johnson, C. 2002. Determinants of loss of mammal species during the Late Quaternary “megafauna” extinctions: life history and ecology, but not body size. Proceedings of the Royal Society B: Biological Sciences 269:2221–2227.']
  • ['Jones, K. E., J. Bielby, M. Cardillo, S. A. Fritz, J. O’Dell, C. D. Orme, K. Safi, et al. 2009. PanTHERIA: a species-level database of life history, ecology, and geography of extant and recently extinct mammals. Ecology 90:2648. Data downloaded on September 29, 2011.']
  • ['Judge, G. G. 1985. The theory and practice of econometrics. Wiley, New York.']
  • ['Koch, P. L., and A. D. Barnosky. 2006. Late Quaternary extinctions: state of the debate. Annual Review of Ecology, Evolution, and Systematics 37:215–250.']
  • ['Kürschner, W. M., Z. Kvaek, and D. L. Dilcher. 2008. The impact of Miocene atmospheric carbon dioxide fluctuations on climate and the evolution of terrestrial ecosystems. Proceedings of the National Academy of Sciences of the USA 105:449–453.']
  • ['Lebreton, J. D., K. P. Burnham, J. Colbert, and D. R. Anderson. 1992. Modeling survival and testing biological hypotheses using marked animals: a unified approach with case studies. Ecological Monographs 62:67–118.']
  • ['Liow, L. H., M. Fortelius, E. Bingham, K. Lintulaakso, H. Mannila, L. Flynn, and N. C. Stenseth. 2008a. Higher origination and extinction rates in larger mammals. Proceedings of the National Academy of Sciences of the USA 105:6097–6102.']
  • ['———. 2008b. Reply to Vilar et al.: sleep or hide, better for survival anytime. Proceedings of the National Academy of Sciences of the USA 105:E57.']
  • ['Liow, L. H., M. Fortelius, K. Lintulaakso, H. Mannila, and N. C. Stenseth. 2009. Lower extinction risk in sleep-or-hide mammals. American Naturalist 173:264–272.']
  • ['Liow, L. H., and J. D. Nichols. 2010. Estimating rates and probabilities of origination and extinction using taxonomic occurrence data: capture-mark-recapture (CMR) approaches. Pages 81–94 in J. Alroy and G. Hunt, eds. Quantitative methods in paleobiology. Vol. 16. Paleontological Society Papers. Paleontological Society. Boulder, CO.']
  • ['Lyons, S. K., F. A. Smith, and J. H. Brown. 2004. Of mice, mastodons and men: human-mediated extinctions on four continents. Evolutionary Ecology Research 6:339–358.']
  • ['Maguire, K. C., and A. L. Stigall. 2009. Using ecological niche modeling for quantitative biogeographic analysis: a case study of Miocene and Pliocene Equinae in the Great Plains. Paleobiology 35:587–611.']
  • ['Maridet, O., and L. Costeur. 2010. Diversity trends in Neogene European ungulates and rodents: large-scale comparisons and perspectives. Naturwissenschaften 97:161–172.']
  • ['Maridet, O., L. Costeur, and S. Legendre. 2012. European Neogene rodent communities: explaining family-level replacements through a spatiotemporal approach. Historical Biology, doi:10.1080/08912963.2012.739170.']
  • ['Marshall, C. R. 1997. Confidence intervals on stratigraphic ranges with nonrandom distributions of fossil horizons. Paleobiology 23:165–173.']
  • ['———. 2010. Using confidence intervals to quantify the uncertainty in the end-points of stratigraphic ranges. Pages 291–316 in J. Alroy and G. Hunt, eds. Quantitative methods in paleobiology. Vol. 16. Paleontological Society Papers. Paleontological Society, Boulder, CO.']
  • ['Martin, R. A. 1992. Generic species richness and body mass in North American mammals: support for the inverse relationship of body size and speciation rate. Historical Biology 6:73–90.']
  • ['McKinney, M. L. 1997. Extinction vulnerability and selectivity: combining ecological and paleontological views. Annual Review of Ecology and Systematics 28:495–516.']
  • ['Mihlbachler, M. C., F. Rivals, N. Solounias, and G. M. Semprebon. 2011. Dietary change and evolution of horses in North America. Science 331:1178–1181.']
  • ['Owen-Smith, N. 1987. Pleistocene extinctions: the pivotal role of megaherbivores. Paleobiology 13:351–362.']
  • ['Pagel, M. 1999. Inferring the historical patterns of biological evolution. Nature 401:877–884.']
  • ['Paleobiology Database. “Measurement Download Request Form.” Accessed January 6, 2012.']
  • ['Paradis, E., B. Bolker, J. Claude, H. S. Cuong, R. Desper, B. Durand, J. Dutheil, et al. 2012. “ape: Analyses of Phylogenetics and Evolution.” Version 3.0-3.']
  • ['Pickford, M. 1989. Dynamics of Old World biogeographic realms during the Neogene: implications for biostratigraphy. Pages 413–442 in E. H. Lindsay, V. Fahlbusch, and P. Mein, eds. European Neogene mammal chronology. Plenum, New York.']
  • ['Pickford, M., and J. Morales. 1994. Biostratigraphy and palaeobiogeography of East Africa and the Iberian peninsula. Palaeogeography, Palaeoclimatology, Palaeoecology 112:297–322.']
  • ['Pinheiro, J., D. Bates, S. DebRoy, D. Sarkar, and R Development Core Team. 2012. “nlme: Linear and Nonlinear Mixed Effects Models.” Version 3.1-103.']
  • ['Polishchuk, L. V. 2010. The three-quarter-power scaling of extinction risk in Late Pleistocene mammals, and a new theory of the size selectivity of extinction. Evolutionary Ecology Research 12:1–22.']
  • ['Purvis, A., C. D. L. Orme, and K. Dolphin. 2003. Why are most species small-bodied? a phylogenetic view. Pages 155–173 in Blackburn, T. M. and Gaston, K. J., ed. Macroecology: concepts and consequences. Blackwell Science, Oxford.']
  • ['R Development Core Team. 2012. R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna. Version 2.15.2.']
  • ['Raia, P., F. Passaro, D. Fulgione, and F. Carotenuto. 2012. Habitat tracking, stasis and survival in Neogene large mammals. Biology Letters 8:64–66.']
  • ['Retallack, G. J. 2007. Cenozoic paleoclimate on land in North America. Journal of Geology 115:271–294.']
  • ['Revell, L. J. 2010. Phylogenetic signal and linear regression on species data. Methods in Ecology and Evolution 1:319–329.']
  • ['———. 2012. “Phytools: Phylogenetic Tools in R Development Page.” Version 0.1–7.']
  • ['Reynolds, J. D. 2003. Life histories and extinction risk. Pages 195–217 in T. M. Blackburn and K. J. Gaston, ed. Macroecology: concepts and consequences. Blackwell Science, Oxford.']
  • ['Simpson, G. G. 1944. Tempo and mode in evolution. Columbia University Press, New York.']
  • ['Smith, F. A., J. H. Brown, J. P. Haskell, S. K. Lyons, J. Alroy, E. L. Charnow, T. Dayan, et al. 2004. Similarity of mammalian body size across the taxonomic hierarchy and across space and time. American Naturalist 163:672–691.']
  • ['Soulé, M. E. 1983. What do we really know about extinction? Pages 111–124 in C. M. Schonewald-Cox, S. M. Chambers, B. MacBryde, and W. L. Thomas, eds. Genetics and conservation: a reference for managing wild animal and plant populations. Benjamin/Cummings, Menlo Park, CA.']
  • ['Stanley, S. M. 1979. Macroevolution: pattern and process. Freeman, San Francisco.']
  • ['Stevens, M. S., and J. B. Stevens. 2007. Family Merycoidodontidae. Pages 157–168 in D. R. Prothero and S. E. Foss, eds. The evolution of artiodactyls. Johns Hopkins University Press, Baltimore.']
  • ['Strömberg, C. A. E. 2011. Evolution of grasses and grassland ecosystems. Annual Review of Earth and Planetary Sciences 39:517–544.']
  • ['Strömberg, C. A. E., and F. A. McInerney. 2011. The Neogene transition from C3 to C4 grasslands in North America: assemblage analysis of fossil phytoliths. Paleobiology 37:50–71.']
  • ['Tedford, R. H., X. Wang, and B. E. Taylor. 2009. Phylogenetic systematics of the North American fossil Caninae (Carnivora: Canidae). Bulletin of the American Museum of Natural History 325:1–218.']
  • ['Tomiya, S. 2013. Data from: Body size and extinction risk in terrestrial mammals above the species level. American Naturalist, Dryad Digital Repository,']
  • ['van Dam, J. A., H. A. Aziz, M. A. Álvarez Sierra, F. J. Hilgen, L. W. van den Hoek Ostende, L. J. Lourens, P. Mein, A. J. van der Meulen, and P. Pelaez-Campomanes. 2006. Long-period astronomical forcing of mammal turnover. Nature 443:687–691.']
  • ['van der Made, J. 1999. Intercontinental relationship Europe-Africa and the Indian subcontinent. Pages 457–472 in G. E. Rössner and K. Heissig, eds. The Miocene land mammals of Europe. Pfeil, Munich.']
  • ['Van Valkenburgh, B., X. Wang, and J. Damuth. 2004. Cope’s Rule, hypercarnivory, and extinction in North American canids. Science 306:101–104.']
  • ['Vermeij, G. J. 2004. Ecological avalanches and the two kinds of extinction. Evolutionary Ecology Research 6:315–337.']
  • ['Viranta, S. 2003. Geographic and temporal ranges of middle and late Miocene carnivorans. Journal of Mammalogy 84:1267–1278.']
  • ['Vrba, E. S. 1992. Mammals as a key to evolutionary theory. Journal of Mammalogy 73:1–28.']
  • ['———. 1995. On the connection between paleoclimate and evolution. Pages 24–45 in E. S. Vrba, G. H. Denton, T. C. Patridge, and L. H. Burckle, eds. Paleoclimate and evolution, with emphasis on human origins. Yale University Press, New Haven CT.']
  • ['Wang, X. 1994. Phylogenetic systematics of the Hesperocyoninae (Carnivora: Canidae). Bulletin of the American Museum of Natural History 221:1–207.']
  • ['Wang, X., R. H. Tedford, and B. E. Taylor. 1999. Phylogenetic systematics of the Borophaginae (Carnivora: Canidae). Bulletin of the American Museum of Natural History 243:1–391.']
  • ['Webb, S. D. 1969. Extinction-origination equilibria in late Cenozoic land mammals of North America. Evolution 23:688–702.']
  • ['———. 1977. A history of savanna vertebrates in the New World. Pt. 1. North America. Annual Review of Ecology and Systematics 8:355–380.']
  • ['———. 1984. Ten million years of mammal extinctions in North America. Pages 189–210 in P. S. Martin and R. G. Klein, eds. Quaternary extinctions: a prehistoric revolution. University of Arizona Press, Tucson.']
  • ['Webb, S. D., R. C. Hulbert, and W. D. Lambert. 1995. Climatic implications of large-herbivore distributions in the Miocene of North America. Pages 91–108 in E. S. Vrba, G. H. Denton, T. C. Patridge, and L. H. Burckle, eds. Paleoclimate and evolution, with emphasis on human origins. Yale University Press, New Haven, CT.']
  • ['Webb, S. D., and N. D. Opdyke. 1995. Global climatic influence on Cenozoic land mammal faunas. Pages 184–208 in National Research Council Panel on Effects of Past Global Change on Life, eds. Effects of global change on life. National Academy Press, Washington, DC.']
  • ['White, G. C. 2012. Program MARK. Version 6.2.']
  • ['White, G. C., and K. P. Burnham. 1999. Program MARK: survival estimation from populations of marked animals. Bird Study 46(suppl.):S120–S138.']
  • ['Woodburne, M. O. 2004. Late Cretaceous and Cenozoic mammals of North America: biostratigraphy and geochronology. Columbia University Press, New York.']
  • ['———. 2007. Phyletic diversification of the Cormohipparion occidentale complex (Mammalia; Perissodactyla, Equidae), late Miocene, North America, and the origin of the Old World Hippotherium datum. Bulletin of the American Museum of Natural History 306:1–138.']
  • ['Zachos, J., M. Pagani, L. Sloan, E. Thomas, and K. Billups. 2001. Trends, rhythms, and aberrations in global climate 65 Ma to present. Science 292:686–693.']
  • ['Zimov, S. A., V. I. Chuprynin, A. P. Oreshko, I. Chapin, F. S., J. F. Reynolds, and M. C. Chapin. 1995. Steppe-tundra transition: a herbivore-driven biome shift at the end of the Pleistocene. American Naturalist 146:765–794.']