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.古生态学数据不仅可用于探究深时时间序列样带的演化趋势，还可用于重建不同时间尺度的生态梯度，这有助于识别现代生态系统中可能存在强相关性的因果关联因子。我们将此类分析应用于伯格曼法则（Bergmann’s Rule）——该法则提出哺乳动物的体温与体型大小之间存在因果关系。伯格曼法则预测，任意地质时段内均应存在纬度梯度：体型更大的分类类群分布于极地，体型更小的分类类群分布于赤道区域。该法则同时预测，此类梯度的强度应随时间发生变化：温暖时期梯度强度减弱，寒冷时期则增强。我们以北美西海岸渐新世-中新世不同地质时段的犬科（canid）和马科（equid）属类群为研究对象，通过重建其体重变化趋势对上述预测开展检验。为便于与现生类群进行对比，我们以现生犬属（Canis）和空齿鹿属（Odocoileus）为对象，沿相同样带重建了其体重数据。在本次分析的17个化石属类群中，仅有2个呈现出与纬度预期的正相关关系，且未发现古温度与体型大小之间存在稳定关联的可靠证据。同样，体型梯度的强度也未随气候的时间变化呈现出可预测的变化规律。即便在本次分析的现生属类群中，清晰梯度的相关证据也并不明确。本研究结果表明，与伯格曼法则相悖，仅温度并非影响体型大小的核心驱动因子；同时也凸显了区域尺度古生态学分析在识别此类驱动因子过程中的重要性。