Data from: Latitudinal body size trends in Oligo-Miocene mammals

Paleoecological data allow not only the study of trends along deep-time chronological transects but can also be used to reconstruct ecological gradients through time, which can help identify causal factors that may be strongly correlated in modern ecosystems. We have applied such an analysis to Bergmann’s Rule, which posits a causal relationship between temperature and body size in mammals. Bergmann’s Rule predicts that latitudinal gradients should exist during any interval of time, with larger taxa towards the poles and smaller taxa towards the equator. It also predicts that the strength of these gradients should vary with time, becoming weaker during warmer periods and stronger during colder conditions. We tested these predictions by reconstructing body mass trends within canid and equid genera at different intervals of the Oligo-Miocene along the West Coast of North America. To allow for comparisons to modern taxa, body mass was reconstructed along the same transect for modern Canis and Odocoileus. Of the 17 fossil genera analyzed, only two showed the expected positive relationship with latitude, nor was there consistent evidence for a relationship between paleotemperature and body mass. Likewise, the strength of body size gradients does not change predictably with climate through time. The evidence for clear gradients is ambiguous even in the modern genera analyzed. These results suggest that, counter to Bergmann’s Rule, temperature alone is not a primary driver of body size and underscore the importance of regional-scale paleoecological analyses in identifying such drivers.

古生态学数据（Paleoecological data）不仅可用于探究深时年代序列样带的变化趋势，还可用于重建随时间演变的生态梯度，这有助于识别在现代生态系统中可能存在强相关性的因果因子。我们将此类分析应用于伯格曼法则（Bergmann’s Rule）——该法则提出了哺乳动物体温与体型大小之间的因果关联。伯格曼法则预测，在任意地质时间区间内均应存在纬度梯度：体型更大的分类群（taxa）分布于极地，体型更小的分类群分布于赤道区域。该法则同时预测，这些梯度的强度会随时间发生变化：在温暖时期梯度强度会减弱，而在寒冷时期则会增强。我们通过重建北美西海岸渐新世-中新世（Oligo-Miocene）不同地质时段内犬科与马科各属的体重变化趋势，对上述预测进行了检验。为便于与现代分类群进行对比，我们以相同的样带标准重建了现代犬属（Canis）与空齿鹿属（Odocoileus）的体重数据。在所分析的17个化石属中，仅有2个属呈现出与纬度相符的正相关关系，同时也未发现古温度（paleotemperature）与体重之间存在稳定关联的一致证据。同样，体型梯度的强度也并未随时间推移和气候的变化呈现出可预测的变化规律。即便在本次分析的现代属类中，关于清晰梯度的证据也仍不明确。这些研究结果表明，与伯格曼法则相悖的是，仅体温并非影响体型大小的主要驱动因素，同时也凸显了开展区域尺度古生态学分析对于识别此类驱动因子的重要性。