Testing for Depéret’s rule (body size increase) in mammals using combined extinct and extant data

Whether or not evolutionary lineages in general show a tendency to increase in body size has often been discussed. This tendency has been dubbed “Cope's rule” but because Cope never hypothesized it, we suggest renaming it after Depéret, who formulated it clearly in 1907. Depéret's rule has traditionally been studied using fossil data, but more recently a number of studies have used present-day species. While several paleontological studies of Cenozoic placental mammals have found support for increasing body size, most studies of extant placentals have failed to detect such a trend. Here, we present a method to combine information from present-day species with fossil data in a Bayesian phylogenetic framework. We apply the method to body mass estimates of a large number of extant and extinct mammal species, and find strong support for Depéret's rule. The tendency for size increase appears to be driven not by evolution toward larger size in established species, but by processes related to the emergence of new species. Our analysis shows that complementary data from extant and extinct species can greatly improve inference of macroevolutionary processes.

演化支是否普遍存在体型增大的趋势，这一议题长期以来广受讨论。该趋势曾被称为“科普法则（Cope's rule）”，但由于科普从未正式提出这一假说，我们建议以1907年首次明确阐述该规律的德佩雷（Depéret）之名重新命名这一演化现象。德佩雷法则（Depéret's rule）传统上多依托化石数据开展研究，而近年来已有多项研究采用现生物种展开相关分析。尽管多项针对新生代有胎盘类哺乳动物的古生物学研究证实了体型增大趋势的存在，但大多数针对现生有胎盘类动物的研究却未能检测到这一规律。本研究提出一种可在贝叶斯系统发育框架下整合现生物种与化石数据信息的分析方法。我们将该方法应用于大量现生与灭绝哺乳动物的体重估算数据集，结果为德佩雷法则提供了强有力的支持证据。体型增大的趋势似乎并非源于已存续物种向大体型方向的演化，而是由与新物种诞生相关的演化过程所驱动。本研究分析表明，整合现生与灭绝物种的互补数据，可大幅提升宏演化过程推断的准确性与可靠性。