Reassessment of <i>Tegehotherium burmeisteri</i> Ameghino 1903–1904 (<i>Notoungulata</i>, <i>Hegetotheriidae</i>) and a new phylogenetic analysis of <i>Hegetotheriidae</i>

Within the notoungulate family Hegetotheriidae, some species have not been analyzed since their original publication more than a century ago. Here we present the first re-evaluation of Tegehotherium burmeisteri, including a detailed description of its holotype in an updated comparative framework, a species presumably coming from the Trelew Member of the Sarmiento Formation (Chubut Province, Argentina). Tegehotherium burmeisteri is included for the first time in a phylogenetic analysis centered in the interrelationships of hegetotheriids and defining clades according to the PhyloCode. Tegehotherium burmeisteri is recovered as a hegetotheriine closely related to Sallatherium and Hegetotherium; Hegetotheriopsis sulcatus is the earliest branch of the clade Hegetotheriidae, whereas Prohegetotherium and Paedotherium turn out to be paraphyletic, reinforcing results obtained in recent studies. The family Hegetotheriidae and both subfamilies, Hegetotheriinae and Pachyrukhinae, are recovered as monophyletic groups and defined phylogenetically, as well as two new clades: Pachyrukhini and Hemihegetotheriomorpha.在南美有蹄类（Notoungulata）的赫格托兽科（Hegetotheriidae）中，部分物种自一个多世纪前首次发表以来尚未得到系统的重新研究。本研究首次对布氏泰格赫托兽（Tegehotherium burmeisteri）开展重新评估，在更新的比较框架下详细描述其正模标本（holotype）；该物种的化石产出层位推测为阿根廷丘布特省萨尔米恩托组（Sarmiento Formation）特雷卢段（Trelew Member）。本研究首次将布氏泰格赫托兽纳入以赫格托兽科类群间亲缘关系为核心的系统发育分析（phylogenetic analysis），并依据系统发育法典（PhyloCode）对分支类群（clade）进行定义。系统发育分析结果显示，布氏泰格赫托兽隶属于赫格托兽亚科（Hegetotheriinae），与萨拉托兽（Sallatherium）及赫格托兽（Hegetotherium）亲缘关系密切；沟痕赫格托拟兽（Hegetotheriopsis sulcatus）为赫格托兽科分支的最基部类群；而前赫格托兽属（Prohegetotherium）与幼兽形兽属（Paedotherium）被证实为并系群（paraphyletic group），该结果印证了近期相关研究的结论。赫格托兽科及其下属的赫格托兽亚科（Hegetotheriinae）与厚齿兽亚科（Pachyrukhinae）均被恢复为单系群（monophyletic group）并完成系统发育定义；此外本研究还建立了两个全新的分支类群：厚齿兽族（Pachyrukhini）与半赫格托兽形类（Hemihegetotheriomorpha）。