Systematic and morphogeometric analyses of Pachyrukhinae (Mammalia, Hegetotheriidae) from the HuayquerÍas, Mendoza (Argentina): biostratigraphic and evolutionary implications

We present new remains of Pachyrukhinae (Hegetotheriidae) from the Huayquerías del Este (Mendoza, Argentina). We identify Tremacyllus impressus, proposing T. subdiminutus as a synonym and providing new data on postcranial bones for this taxon. Tremacyllus specimens from Mendoza reveal a wide and continuous morphological variation that encompasses the morphological differences of species previously considered valid, emphasizing the need for a systematic study focused on all representatives of the genus. We also recognize Paedotherium typicum, which shows a combination of features differing from other species of the genus. The large sample allows us to improve the diagnosis for both the genus Tremacyllus and the species T. impressus and P. typicum. Both species coexist in the Huayquerías Formation; T. impressus is also present in the Tunuyán Formation, whereas the specimens recognized as Paedotherium in this unit were not identifiable at species level. Applying geometric morphometric methods on the dentition, we partially support the taxonomic decisions. We present the first phylogenetic analysis including all the species of Tremacyllus and Paedotherium, using morphological characters of skull and postcranium. According to our results, Tremacyllus is a monophyletic group supported by two synapomorphies, whereas Paedotherium is paraphyletic, in agreement with the prior hypothesis. The record of Paedotherium typicum presented here extends the biochron of this taxon into the late Miocene, which is relevant for establishing biostratigraphic and paleobiogeographic affinities with other Miocene localities. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: Vera, B., and M. D. Ercoli. 2018. Systematic and morphogeometric analyses of Pachyrukhinae (Mammalia, Hegetotheriidae) from the Huayquerías, Mendoza (Argentina): biostratigraphic and evolutionary implications. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2018.1473410.本研究报道了采自阿根廷门多萨省东韦克耶里亚斯（Huayquerías del Este）地点的厚吻亚科（Pachyrukhinae，赫格托兽科Hegetotheriidae）新材料。本研究鉴定出印痕特马赛兽（Tremacyllus impressus），将小型特马赛兽（Tremacyllus subdiminutus）归为其同物异名，并为该分类单元（taxon）提供了全新的颅后骨骼（postcranial bones）研究数据。采自门多萨省的特马赛兽属（Tremacyllus）标本展现出广泛且连续的形态变异，涵盖了此前被认定为有效物种的形态差异，这凸显出针对该属所有类群开展系统性研究的必要性。本研究同时鉴定出典型幼兽（Paedotherium typicum），该物种的特征组合与该属其他物种存在显著差异。本次研究的大尺寸样本量，使得我们能够完善特马赛兽属（Tremacyllus）以及印痕特马赛兽（T. impressus）、典型幼兽（P. typicum）的分类鉴别特征。上述两个物种均共存于韦克耶里亚斯组（Huayquerías Formation）中；印痕特马赛兽（T. impressus）同时见于图努扬组（Tunuyán Formation），而该地层中被归为幼兽属（Paedotherium）的标本无法鉴定至物种水平。本研究通过对齿列应用几何形态测量法（geometric morphometric methods），部分验证了本次研究的分类学判定。本研究首次开展了涵盖特马赛兽属（Tremacyllus）与幼兽属（Paedotherium）所有物种的系统发育分析，分析采用头骨与颅后骨骼的形态学特征作为依据。分析结果显示，特马赛兽属（Tremacyllus）为单系群（monophyletic group），得到2项共近裔性状（synapomorphies）的支持；而幼兽属（Paedotherium）为并系群（paraphyletic），这与此前的假说相一致。本次报道的典型幼兽（Paedotherium typicum）化石记录，将该分类单元的生物年代（biochron）延伸至晚中新世（late Miocene），这对于确立其与其他中新世地点的生物地层学（biostratigraphic）及古生物地理学（paleobiogeographic）联系具有重要意义。补充数据：本文的补充材料可于www.tandfonline.com/UJVP免费获取。本文引用格式：Vera B. 与 Ercoli M. D.，2018年。阿根廷门多萨省韦克耶里亚斯地区厚吻亚科（哺乳纲，赫格托兽科Hegetotheriidae）的系统分类与几何形态测量分析：生物地层学及演化意义。《脊椎动物古生物学杂志》（Journal of Vertebrate Paleontology）。DOI: 10.1080/02724634.2018.1473410。