Data from: Phylogeny, macroevolutionary trends and historical biogeography of sloths: insights from a Bayesian morphological clock analysis

Sloths, like other xenarthrans, are an extremely interesting group of mammals that, after a long history of evolution and diversification in South America, became established on islands in the Caribbean and later reached North America during the Great American Biotic Interchange. In all three regions they were part of the impressive Pleistocene megafauna. Most taxa became extinct and only two small, distantly related tree-dwelling genera survived. Here we incorporate several recently described genera of sloths into an assembled morphological data supermatrix and apply Bayesian inference, using phylogenetic and morphological clock methods, to 64 sloth genera. Thus, we investigate the evolution of the group in terms of the timing of divergence of different lineages and their diversity, morphological disparity and biogeographical history. The phylogeny obtained supports the existence of the commonly recognized clades for the group. Our results provide divergence time estimates for the major clades within Folivora that could not be dated with molecular methods. Lineage diversity shows an early increase, reaching a peak in the Early Miocene followed by a major drop at the end of the Santacrucian (Early Miocene). A second peak in the Late Miocene was also followed by a major drop at the end of the Huayquerian (Late Miocene). Both events show differential impact at the family level. After that, a slight Plio-Pleistocene decline was observed before the marked drop with the extinction at the end of the Pleistocene. Phenotypic evolutionary rates were high during the early history of the clade, mainly associated with Mylodontidae, but rapidly decreased to lower values around 25 Ma, whereas Megalonychidae have lower values at the beginning followed by a steady increase, peaking during the Late Miocene and the Pliocene. Morphological disparity showed a similar trend, with an early increase, followed by a slowly increasing phase through the Late Oligocene and Early Miocene, and ending with another increase beginning at the middle of the Miocene. Biogeographic analysis showed southern South America as the most probable area of origin of the clade and the main region in which the early diversification events took place. Both Megatheriinae and Nothrotheriinae basal nodes were strongly correlated with Andean uplift events, whereas the early history of Mylodontidae is closely associated with southern South America and also shows an early occupation of the northern regions. Within Megalonychidae, our results show Choloepus as a descendant of an island dispersing ancestor and a probable re-ingression to South America by a clade that originated in Central or North America.

树懒与其他异关节总目（Xenarthrans）动物一样，是一类极具研究价值的哺乳动物类群。它们在南美洲经历了漫长的演化与分化历程后，成功定居于加勒比海诸岛，并在北美南美生物大交换（Great American Biotic Interchange）时期抵达北美洲。在这三大区域中，树懒均属于更新世（Pleistocene）标志性巨型动物群的组成部分。绝大多数树懒类群已灭绝，仅存2个体型小巧、亲缘关系较远的树栖属。本研究将多个近年新定名的树懒属纳入整合的形态学数据超级矩阵，采用贝叶斯推断（Bayesian inference）结合系统发育与形态钟模型方法，对64个树懒属展开分析。借此，我们从不同谱系的分化时间、类群多样性、形态分异度及生物地理演化历史入手，探究该类群的演化历程。本研究得到的系统发育树支持该类群已被广泛认可的演化支（clade）划分。我们的结果为树懒亚目（Folivora）内各大演化支提供了此前无法通过分子手段估算的分化时间。谱系多样性呈现早期快速增长，在早中新世达到峰值，随后在圣克鲁西亚期（Santacrucian，早中新世）结束时出现大幅下降。晚中新世曾出现第二次多样性峰值，随后又在瓦基里安期（Huayquerian，晚中新世）结束时再度大幅衰退，这两次事件对各科的影响存在显著差异。此后，在上新世-更新世时期多样性略有下降，最终在更新世末期的大规模灭绝事件中彻底锐减。表型演化速率在该演化支的早期历史中处于较高水平，这一特征主要与磨齿兽科（Mylodontidae）相关，但在约2500万年前快速回落至较低水平；而大地懒科（Megalonychidae）的演化速率则初始较低，随后持续攀升，在晚中新世至上新世时期达到峰值。形态分异度的变化趋势与之相似：早期快速增长，随后在渐新世晚期至早中新世时期进入缓慢上升阶段，最终在中新世中期再度迎来增长。生物地理分析显示，南美洲南部是该演化支最可能的起源地，也是早期分化事件的主要发生区域。大地懒亚科（Megatheriinae）与诺氏懒兽亚科（Nothrotheriinae）的基部节点均与安第斯山脉隆升事件高度相关；而磨齿兽科（Mylodontidae）的早期演化历史与南美洲南部紧密关联，同时也很早就占据了北部区域。在大地懒科（Megalonychidae）内部，本研究结果显示二趾树懒属（Choloepus）是一支通过岛屿扩散的祖先类群的后裔，且存在一支起源于中美洲或北美洲的演化支重新迁入南美洲的可能性。