BODY-MASS TRENDS


649


FIGURE 2. Latitudinal body-mass gradients in modern Odocoileus and fossil equids. Land mammal age subdivisions are denoted by abbreviations (Ba, Barstovian; Cl, Clarendonian; Hh, Hemphillian). Spearman’s rho (Ρ) and p-value are indicated for each relationship.


Table 2). Of these, only two equids, early Barstovian hipparionin Merychippus (p=0.0005) and late late Hemphillian Dinohippus (p=0.00009), show the significant positive rela- tionship with latitude predicted by Bergmann’s rule. In total, five early Barstovian genera were present in sufficient numbers from localities for which climate could be reconstructed to directly analyze the relationship between temperature and body mass. In only one of these taxa (hipparionin Merychippus)was asignificant (p=0.0007) negative correlation present (Figs. 4 and 5, Table 3). Ten genera (nine horses and one canid) have


been found at both coastal and inland sites from the same interval and at the comparable lati- tudes, and these were used to test for differences in body size betweenmarine-mediated and rain shadow climates (Table 4). In only one case (middle Clarendonian Pliohippus from the San Francisco Bay Area and the San Joaquin valley) is there a significant difference between body mass between the two regions. The second series of analyses tested for a


relationship between climate and body size by reconstructing body-mass trends in modern


taxa fromcolder climates thanwere represented at any point in the Oligo-Miocene and by directly comparing body mass to mean annual temperature. Of the two Recent genera ana- lyzed, Canis shows a significant relationship between latitude and body mass (p=0.0006) but Odocoileus does not (Figs. 2 and 3, Table 2). Likewise, neither genus showed a significant relationship between mean annual temperature and body mass (Figs. 4 and 5, Table 3). In total, two early Barstovian genera and one Recent genus showed the predicted positive relation- ship with latitude (Figures 2 and 3, Table 2), while only one early Barstovian genus (and no modern genera) showed the expected negative relationship with temperature.


Discussion


Hypothesis Tests The findings of this study do not support


Bergmann’s rule in either modern or Oligo- Miocene ecosystems. The first prediction derived from Bergmann’s (1847) model sug- gests that, in any given interval, body size


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