Data from: Oligo-Miocene climate change and mammal body size evolution in the northwest United States a test of Bergmann's Rule

Whether or not climate plays a causal role in mammal body-size evolution is one of the longest-standing debates in ecology. Bergmann's Rule, the longest-standing model addressing this topic, posits that geographic body-mass patterns are driven by temperature, whereas subsequent research has suggested that other ecological variables, particularly precipitation and seasonality, may be the major drivers of body-size evolution. While paleoecological data provide a unique and crucial perspective on this debate, paleontological tests of Bergmann's rule and its corollaries have been scarce. We present a study of body-size evolution in three ecologically distinct families of mammal (equids, canids, and sciurids) during the Oligo-Miocene of the northwest United States, an ideal natural laboratory for such studies because of its rich fossil and paleoclimatic records. Body-size trends are different in all three groups, and in no case is a significant relationship observed between body size and any climatic variable, counter to what has been observed in modern ecosystems. We suggest that for most of the Cenozoic, at least in the Northwest, body mass has not been driven by any one climatic factor but instead has been the product of complex interactions between organisms and their environments, though the nature of these interactions varies from taxon to taxon. The relationship that exists between climate and body size in many groups of modern mammals, therefore, is the exception to the rule and may be the product of an exceptionally cool and volatile global climate. As anthropogenic global warming continues and ushers in climatic conditions more comparable to earlier intervals of the Cenozoic than to the modern day, models of corresponding biotic variables such as body size may lose predictive power if they do not incorporate paleoecological data.气候是否对哺乳动物体型演化存在因果影响，是生态学领域最经久不衰的争议议题之一。伯格曼法则（Bergmann's Rule）作为该领域最老牌的相关理论模型，提出地理体型大小的分布格局由温度驱动；而后续研究则表明，其他生态变量——尤其是降水与季节节律——或许才是体型演化的主要驱动因素。尽管古生态学数据为该争议提供了独特且关键的研究视角，但针对伯格曼法则及其推论的古生物学检验却极为匮乏。本研究聚焦美国西北部渐新世-中新世（Oligo-Miocene）时期三个生态特征迥异的哺乳动物类群：马科（equids）、犬科（canids）与松鼠科（sciurids）的体型演化。该区域拥有丰富的化石与古气候记录，是开展此类研究的理想天然实验室。三个类群的体型演化趋势各不相同，且未在任何类群中发现体型与任一气候变量间存在显著关联，这与现代生态系统中的观测结果相悖。我们认为，至少在美国西北部区域，新生代（Cenozoic）大部分时期的哺乳动物体型并非由单一气候因子驱动，而是生物与环境间复杂相互作用的产物——尽管这类相互作用的本质因类群而异。因此，诸多现代哺乳动物类群中观测到的气候与体型间的关联，实则属于该法则的例外情形，其成因或许与异常寒冷且波动剧烈的全球气候有关。随着人为全球变暖持续推进，当前的气候条件愈发趋近新生代早期阶段而非现代环境，若未纳入古生态学数据，诸如体型这类相关生物变量的预测模型或将丧失其预测能力。