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 had lower rates 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.

译文

象其他的雪生动物一样,懒惰是一群非常有趣的哺乳动物,在南美经历了漫长的进化和多样化历史之后,它们在加勒比海的岛屿上建立起来,并随后在“大美洲生物交换”中到达了北美。在所有三个地区,它们都是令人印象深刻的更新世大型动物群的一部分。大多数分类单元都灭绝了,只有两个遥远的,与树木有远缘亲缘关系的属幸免于难。在这里,我们将几个最近描述的树懒属植物合并到一个组装的形态学数据超级矩阵中,并使用系统发育和形态学时钟方法对64个树懒属植物应用贝叶斯推断。因此,我们根据不同谱系的发散时间及其多样性,形态差异和生物地理历史来研究该群体的演变。获得的系统发育支持该群体公认的进化枝的存在。我们的结果提供了无法用分子方法确定的主要叶片进化枝时间的估计。世袭多样性显示出早期增加,在中新世早期达到顶峰,随后在圣塔科鲁阶(中新世早期)大幅下降。中新世晚期的第二个高峰之后是Huayquerian(晚中新世)末期的大幅下降。这两个事件在家庭层面上都显示出不同的影响。在那之后,观察到轻微的上新世更新世下降,然后明显下降,而在更新世末期灭绝。在进化枝的早期,表型进化率很高,主要与Mylodontidae有关,但是在25 Ma左右迅速下降到较低的值,而Megalonychidae在开始时率较低,随后稳定增长,在中新世和上新世晚期达到顶峰。 。形态差异表现出相似的趋势,即早期增加,随后是渐新世晚期和中新世早期缓慢增加的阶段,最后在中新世中期开始增加。生物地理学分析表明,南美南部是进化枝最有可能的起源地区,也是发生早期多样化事件的主要地区。 Megatheriinaee和Nothrotheriinae基底节都与安第斯山隆升事件密切相关,而Mylodontidae的早期历史与南美南部紧密相关,也显示了北部地区的早期占领。在Megalonychidae内,我们的研究结果表明,梭罗普斯是岛屿散布祖先的后裔,并可能起源于中美洲或北美洲的进化枝重新进入南美。

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