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 <i>Hegetotheriidae</i>, some species have not been analyzed since their original publication more than a century ago. Here we present the first re-evaluation of <i>Tegehotherium burmeisteri</i>, 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). <i>Tegehotherium burmeisteri</i> is included for the first time in a phylogenetic analysis centered in the interrelationships of hegetotheriids and defining clades according to the PhyloCode. <i>Tegehotherium burmeisteri</i> is recovered as a hegetotheriine closely related to <i>Sallatherium</i> and <i>Hegetotherium</i>; <i>Hegetotheriopsis sulcatus</i> is the earliest branch of the clade <i>Hegetotheriidae</i>, whereas <i>Prohegetotherium</i> and <i>Paedotherium</i> turn out to be paraphyletic, reinforcing results obtained in recent studies. The family <i>Hegetotheriidae</i> and both subfamilies, <i>Hegetotheriinae</i> and <i>Pachyrukhinae</i>, are recovered as monophyletic groups and defined phylogenetically, as well as two new clades: <i>Pachyrukhini</i> and <i>Hemihegetotheriomorpha</i>.