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JOHN D. ORCUTT AND SAMANTHA S. B. HOPKINS


this analysis is at odds with the findings not only of Bergmann (1847) but also with themore recent research on body-size trends through time by Smith et al. (2010) and Saarinen et al. (2014). This discrepancy can likely be explained in part by methodological differences. Smith et al. (2010) and Saarinen et al. (2014) examined maximum body-size trends through time on a global scale, in both cases finding a correlation between temperature and body mass. As dis- cussed above, the large-scale relationship between climate and environmental change over the course of the Cenozoic means that any analysis carried out at the global scale could yield results that seemingly support Bergmann’s rule sensu stricto, when in fact a more complex model, such as the one proposed by Lovegrove and Mowoe (2013), might better explain any patterns observed. It is important to supplement such analyses with studies of trends at a smaller scale in order to more directly observe the degree to which climate has driven body-size evolution. Our analysis of body-size trends along theWest Coast of North America within genera from three families suggests that temperature alone likely does not drive body-size evolution. This may not be true for all taxa at all times and in all places.


The lack of support for Bergmann’srule in


Lovegrove and Mowoe (2013), for example, find some support for Bergmann’s rule in cold- adapted taxa such as castorids and marmots, and it is possible that temperature and other climatic variables play a more important role in shaping body-size patterns in colder climates, such as those characterizing the Pliocene and Pleistocene, or in different regions. While this study does not support a simple relationship between climate and body size, determining whether there are conditions under which such a relationship does exist, or whether body size in certain taxa is more tightly correlated with temperature, is certain to remain a major focus of ecological research. While the research detailed here is by no means the final word on the subject, it demonstrates, along with the research of Gingerich (2003), Smith et al. (2010), Lovegrove and Mowoe (2013), and Saarinen et al. (2014), that paleontology provides a unique and invaluable perspective on a very old debate and that paleoecology should play a


major role in future tests of Bergmann’srule and its corollaries.


Acknowledgments As a collections-based analysis, this project


would have been impossible without the assis- tance of the collections staff at the repositories visited, and for this assistance we would like to thank J. Galkin (American Museum of Natural History); M. Thompson (Idaho Museum of Natural History); J. Samuels and C. Schierup (John Day Fossil Beds National Monument); S. McLeod,V.Rhue, andG.Takeuchi(Natural History Museum of Los Angeles County); A. Farke (Raymond Alf Museum); E. Scott (San Bernardino County Museum); G. Bromm and R. Hilton (Sierra College Museum of Natural History);K.Randall (San DiegoNatural History Museum); S. Shelton (South Dakota School of Mines and Technology); I. Ferrusquía Villafranca, M. Perrilliat Montoya, and V. Romero Mayén (Universidad Nacional Autónoma de Mexico); P. Holroyd and S. Tomiya (University of California Museum of Paleontology); and R. Eng, C. Sidor, C. Richards, and J. Bradley (University ofWashington Burke Museum). We would also like to thank the collections staffs of the National Museum of Natural History, University of Alaska Museum of the North, University of California Museum of Vertebrate Zoology, University of New Mexico Museum of Southwest Biology, and University of Washington Burke Museum for digitizing and making available their collec- tions of Recent mammals. M. Kohn (Boise State University) and J. Myers (Western Oregon University) provided valuable discussions of paleoclimatic proxies and data, and other mem- bers of the University of Oregon vertebrate paleontology program, especially E. Davis and T. Fremd, provided valuable feedback through- out. Three anonymous reviewers provided insightful commentary on an earlier version of this manuscript, and their comments and sug- gestions are much appreciated. This project was originally undertaken as part of J.D.O.’sdisserta- tion research, and he would like to thank his committeemembers (G.Retallack,R.Dorsey, and S. Frost) for their valuable input and the University of Oregon Department of Geological Sciences for funding.


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