Data from: Influence of Tertiary paleoenvironmental changes on the diversification of South American mammals: a relaxed molecular clock study within xenarthrans.

BACKGROUND: Comparative genomic data among organisms allow the reconstruction of their phylogenies and evolutionary time scales. Molecular timings have been recently used to suggest that environmental global change have shaped the evolutionary history of diverse terrestrial organisms. Living xenarthrans (armadillos, anteaters and sloths) constitute an ideal model for studying the influence of past environmental changes on species diversification. Indeed, extant xenarthran species are relicts from an evolutionary radiation enhanced by their isolation in South America during the Tertiary era, a period for which major climate variations and tectonic events are relatively well documented.

RESULTS: We applied a Bayesian approach to three nuclear genes in order to relax the molecular clock assumption while accounting for differences in evolutionary dynamics among genes and incorporating paleontological uncertainties. We obtained a molecular time scale for the evolution of extant xenarthrans and other placental mammals. Divergence time estimates provide substantial evidence for contemporaneous diversification events among independent xenarthran lineages. This correlated pattern of diversification might possibly relate to major environmental changes that occurred in South America during the Cenozoic.

CONCLUSIONS: The observed synchronicity between planetary and biological events suggests that global change played a crucial role in shaping the evolutionary history of extant xenarthrans. Our findings open ways to test this hypothesis further in other South American mammalian endemics like hystricognath rodents, platyrrhine primates, and didelphid marsupials.

背景（BACKGROUND）：物种间的比较基因组学数据可用于重建其系统发育关系与演化时间尺度。近年来，分子定年手段被用于佐证全球环境变化塑造了多样陆生生物的演化历程。现生异关节总目（xenarthrans）动物（包括犰狳、食蚁兽和树懒）是研究古环境变化对物种分化影响的理想模型类群。事实上，现生异关节总目物种是第三纪时期因隔离于南美洲而迎来演化辐射的孑遗类群；该时期的重大气候波动与构造事件均已有较为充分的研究记录。
结果（RESULTS）：本研究针对3个核基因位点采用贝叶斯（Bayesian）分析方法，在放松分子钟假设的前提下，同时考量不同基因间的演化动态差异，并纳入古生物学研究的不确定性。最终得到了现生异关节总目动物与其他胎盘类哺乳动物的演化分子时间尺度。物种分化时间估算结果为独立异关节总目支系间的同步分化事件提供了充分佐证。这种具有相关性的分化模式，可能与新生代时期南美洲发生的重大环境变化存在关联。
结论（CONCLUSIONS）：本研究观测到的地质事件与生物演化事件的同步性，表明全球环境变化在塑造现生异关节总目动物的演化历程中发挥了关键作用。本研究的发现为后续在其他南美洲特有哺乳动物类群（如豪猪型啮齿类（hystricognath rodents）、阔鼻猴类（platyrrhine primates）以及负鼠科有袋类（didelphid marsupials））中验证该假说提供了可行路径。