A new genus of Interatheriinae (Interatheriidae, Notoungulata) from the Santa Cruz Formation (early–middle Miocene), Santa Cruz Province, Argentina, and the revision of the genus <i>Cochilius</i> Ameghino, 1902
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Interatheriinae is one of the most derived subfamilies of South American notoungulates. Several interatheriines have been described since the 19th century, but most of them have not been revised, or been formally re-examined, for more than a century. Most interatheriine taxa were erected based on materials collected from Argentinean Patagonia, particularly from the Santa Cruz Formation (early–middle Miocene), Santa Cruz Province. Within the framework of an exhaustive unpublished systematic revision of Interatheriinae (early Oligocene–late Miocene), we studied the holotype of Santacrucian <i>Icochilus undulatus</i>, leading to the recognition of a new monospecific genus, <i>Neoicochilus</i> gen. nov., and the new combination <i>N. undulatus</i>. In addition, we formalize the taxonomic revision of <i>Cochilius</i>, proposing the following: <i>Paracochilius</i> is the junior synonym of <i>Cochilius</i>; <i>Cochilius</i> consists of <i>C. volvens</i>, <i>C. fumensis</i>, and <i>C. brevirostrus</i>; <i>Paracochilius chubutensis</i> and <i>Protypotherium minor</i> are junior synonyms of <i>Cochilius brevirostrus</i>; <i>Cochilius pendens</i> is the junior synonym of <i>Cochilius columnifer</i>; and the holotype of <i>Cochilius columnifer</i> exhibits the diagnostic features of <i>Protypotherium</i>, so we propose the new combination <i>Protypotherium columnifer</i>, pending publication of our thorough taxonomic revision of <i>Protypotherium</i>. Our taxonomic scheme is supported by a cladistic analysis, which places <i>Neoicochilus undulatus</i> in a derived position within Interatheriinae, as the sister taxon of the monophyletic genus <i>Cochilius</i>, and the clade <i>Neoicochilus</i> plus <i>Cochilius</i> positioned as the sister taxon of <i>Interatherium</i>. Our phylogenetic results support the monophyly of Miocene interatheriines.
