Shockey Bruce J, Billet Guillaume, Salas-Gismondi Rodolfo
Biology Department, Manhattan College Parkway, Manhattan College, New York Department of Vertebrae Paleontology, American Museum of Natural History Yale Peabody Museum of Natural History, Yale University, New Haven, CT.; Email:
Sorbonne Universités, CR2P, UMR CNRS 7207, CP 38, Muséum national d'Histoire naturelle, Univ Paris 06, 8 rue Buffon, 75005 Paris, France.; Email:
Zootaxa. 2016 May 18;4111(5):565-83. doi: 10.11646/zootaxa.4111.5.3.
Herein we describe a new species of early diverging mesotheriid notoungulate from the late Oligocene of Moquegua, Peru. This taxon, Trachytherus ramirezi sp. nov., is distinctive in terms of a few characteristics that appear plesiomorphic as compared to those of other described mesotheriids, even other species referred to Trachytherus. Such plesiomorphic traits include the absence of an upper diastema and a lack of heart-shaped incisive foramina, traits that are generally present in other mesotheriids. Our phylogenetic analysis of described early divergent mesotheriids indicates that T. ramirezi was the earliest to diverge. This analysis also confirms the paraphyletic nature of the "genus" Trachytherus. Geographically, T. ramirezi clusters among T. alloxus, T. subandinus, and T. spegazzinianus, all of which are known from a discrete region in the middle latitudes of western South America that we refer to as the Bolivian Orocline Region (BOR). Our palaeobiogeographic reconstruction using maximum parsimony identifies the BOR as a possible ancestral area for the Mesotheriidae and as an important region for their diversification. For the more exclusive Mesotheriinae, the BOR was reconstructed as the ancestral area, an area from which some mesotheriines would have later dispersed to southern South America. Uncertainty concerning the ancestral area, for the Mesotheriidae-which could be BOR or southern South America area (or both)-is possibly due to the ignorance of the phylogenetic affinities for the undescribed mesotheriid remains reported from Tinguirirican localities. The present description of T. ramirezi therefore adds to the high taxonomic diversity of early mesotheriid species in the relatively small area of the BOR and emphasizes the likely role played by this topographically dynamic area on mesotheriid evolution during a significant time in the history of the clade.
在此我们描述了一种来自秘鲁莫克瓜晚渐新世的早期分化的中兽科南方有蹄类新物种。这个分类单元，拉米雷斯粗面兽（Trachytherus ramirezi sp. nov.），在一些特征方面很独特，与其他已描述的中兽科动物相比，甚至与其他归入粗面兽属的物种相比，这些特征显得更为原始。这些原始特征包括没有上颌间隙以及缺乏心形切牙孔，而这些特征在其他中兽科动物中通常是存在的。我们对已描述的早期分化的中兽科动物进行的系统发育分析表明，拉米雷斯粗面兽是最早分化出来的。该分析还证实了粗面兽“属”的并系性质。在地理上，拉米雷斯粗面兽与异粗面兽（T. alloxus）、亚安第斯粗面兽（T. subandinus）和斯氏粗面兽（T. spegazzinianus）聚在一起，所有这些物种都来自南美洲西部中纬度的一个离散区域，我们将其称为玻利维亚斜山区（BOR）。我们使用最大简约法进行的古生物地理重建将玻利维亚斜山区确定为中兽科可能的祖先区域以及它们多样化的重要区域。对于更为独特的中兽亚科来说，玻利维亚斜山区被重建为祖先区域，一些中兽亚科动物后来从这个区域扩散到了南美洲南部。关于中兽科祖先区域的不确定性——可能是玻利维亚斜山区或南美洲南部地区（或两者皆是）——可能是由于对廷吉里里坎地区报道的未描述的中兽科动物化石残骸的系统发育亲缘关系缺乏了解。因此，拉米雷斯粗面兽的当前描述增加了玻利维亚斜山区相对较小区域内早期中兽科物种的高分类多样性，并强调了这个地形动态区域在该类群历史上的重要时期对中兽科进化可能发挥的作用。
