Widespread loss of mammalian lineage and dietary diversity in the early Oligocene of Afro-Arabia

Diverse lines of geological and geochemical evidence indicate that the Eocene-Oligocene transition (EOT) marked the onset of a global cooling phase, rapid growth of the Antarctic ice sheet, and a worldwide drop in sea level. Paleontologists have established that shifts in mammalian community structure in Europe and Asia were broadly coincident with these events, but the potential impact of early Oligocene climate change on the mammalian communities of Afro-Arabia has long been unclear. Here we employ dated phylogenies of multiple endemic Afro-Arabian mammal clades (anomaluroid and hystricognath rodents, anthropoid and strepsirrhine primates, and carnivorous hyaenodonts) to investigate lineage diversification and loss since the early Eocene. These analyses provide the first non-anecdotal evidence for widespread mammalian extinction in the early Oligocene of Afro-Arabia, with almost two-thirds of peak late Eocene diversity lost in these clades by ~30 Ma. Using homology-free dental topographic metrics, we further demonstrate that the loss of Afro-Arabian rodent and primate lineages was associated with a reduction in molar occlusal topographic disparity, suggesting a correlated loss of dietary diversity. These results raise new questions about the relative importance of global versus local influences in shaping the evolutionary trajectories of Afro-Arabia’s endemic mammals during the Oligocene.

多类地质与地球化学证据表明，始新世-渐新世转换期（Eocene-Oligocene Transition, EOT）标志着全球降温阶段的启动、南极冰盖的快速扩张，以及全球性海平面下降。古生物学家已证实，欧洲与亚洲的哺乳动物群落结构变化与上述事件大体同步，但长期以来，早渐新世气候变化对非洲-阿拉伯区哺乳动物群落的潜在影响始终不明。本研究利用多个非洲-阿拉伯区特有哺乳动物支系的定年系统发育树（包括鳞尾松鼠超科、豪猪型啮齿类、类人猿与原猴亚目灵长类，以及食肉型鬣齿兽类），探究自始新世早期以来的支系分化与消失情况。本分析首次为非洲-阿拉伯区早渐新世广泛存在的哺乳动物灭绝事件提供了实证依据：至约30 Ma时，上述支系的晚始新世峰值多样性已有近三分之二丧失。本研究进一步采用无同源性要求的牙齿地形学指标，证实非洲-阿拉伯区啮齿类与灵长类支系的消失与臼齿咬合面地形差异度降低存在关联，这表明其食性多样性也同步下降。上述研究结果为探讨渐新世期间全球与区域因素对非洲-阿拉伯区特有哺乳动物演化轨迹的相对重要性，提出了新的科学问题。