Nemolestes and Procladosictis are Eocene sparassodonts of controversial affinities. Nevertheless, despite the poor preservation of their holotypes, several other specimens have been tentatively assigned to these genera, as exemplified by some isolated teeth from the Itaboraí and Laguna Fría faunas. Here, we revise specimens referred to Nemolestes and Procladosictis from Itaboraí, Laguna Fría and Ameghino’s collection. Nemolestes differs from Patene in its more reduced metaconid, and “carnassialized” m4 (with reduced talonid and talonid cuspids, except the hypoconulid), features that make it possible to identify specimens from Itaboraí and Laguna Fría as Nemolestes. This taxon occurred from the early Eocene (Itaboraian SALMA) to the middle Eocene (Casamayoran SALMA). Nemolestes represents the oldest known hypercarnivorous sparassodont. The inclusion of Nemolestes and Procladosictis in a comprehensive phylogenetic analysis recovered them in a polytomy as the sister taxa of Borhyaenoidea and a new unnamed clade that includes Lycopsis, Dukecynus, Hathliacynidae, Hondadelphys and Stylocynus. Nemolestes shares with these taxa, but not Patene, the presence of a “carnassialized” m4. Nemolestes differs from known borhyaenoids in the absence of a medially positioned protoconid and short anterolabial cingulid. Therefore, Nemolestes is an early lineage of Sparassodonta. “Procladosictis erecta” is a lower premolar of the unnamed clade, as it shows symmetric walls and a small precingulid. "Procladosictis erecta" should be, in fact, referred to Procladosictis. Our phylogenetic analysis indicates that during the early middle Eocene (Laguna Fría and La Barda faunas), the unnamed clade and Borhyaenoidea had already diverged. Therefore, the evolutionary history of these groups is older than previously thought.

Nemolestes和Procladosictis是具有有争议亲缘关系的始新世锯齿齿兽。然而，尽管它们的正模标本保存不佳，但其他几个标本已被初步归入这些属，例如来自 Itaboraí 和 Laguna Fría 动物群的一些孤立牙齿。在这里，我们修改了来自 Itaboraí、Laguna Fría 和 Ameghino 收藏的Nemolestes和Procladosictis标本。Nemolestes与Patene的不同之处在于它的 metaconid 和“carnassialized”m4（具有减少的 talonid 和 talonid 尖牙，除了 hypoconulid），这些特征使得可以将 Itaboraí 和 Laguna Fría 的标本识别为Nemolestes. 该分类群发生于始新世早期 (Itaboraian SALMA) 至始新世中期 (Casamayoran SALMA)。Nemolestes代表已知最古老的超级肉食性蛇齿兽。将Nemolestes和Procladosictis包含在综合系统发育分析中，将它们作为 Borhyaenoidea 的姊妹类群和一个新的未命名进化枝（包括Lycopsis、Dukecynus、 Hathliacynidae 、Hondadelphys和Stylocynus ）进行了多分类。Nemolestes与这些分类单元共享，但不是Patene，存在“carnassialized”m4。水螅与已知的 borhyaenoids 的不同之处在于没有位于内侧的原锥虫和短的前唇前扣带。因此，Nemolestes是齿齿象属的一个早期谱系。“ Procladosictis erecta ”是未命名进化枝的下前臼齿，因为它显示对称的壁和一个小的前齿。“ Procladosictis erecta ”其实应该是指Procladosictis。我们的系统发育分析表明，在始新世中期早期（Laguna Fría 和 La Barda 动物群），未命名的进化枝和 Borhyaenoidea 已经分化。因此，这些群体的进化历史比之前认为的要古老。