The Paleogene record of caviomorph rodents has substantially increased over the last decades, and their evolutionary history better understood by the discovery of their earliest representatives, so far recorded in several pre-Deseadan localities in Peruvian Amazonia. We report here the discovery of new caviomorph fossils from the Balsayacu area in Peru (TAR-55/TAR-55bis, TAR-76 and TAR-77 localities, San Martín Department). The study of this new material reveals the occurrence of four caviomorph taxa in these localities: Balsayacuy huallagaensis gen. et sp. nov., Chachapoyamys kathetos gen. et sp. nov. and Caviomorpha gen. et sp. indet. 1 and 2. It allows the revision and refinement of taxonomic assignments of previously described specimens. The first three taxa have a primitive dental pattern, as that characterizing stem Caviomorpha recorded in pre-Deseadan localities of Peru (Eocene localities of Contamana and ?late Eocene/early Oligocene Santa Rosa). We support here an Eocene age for the Balsayacu section due to the complete absence of morphologically derived taxa representing modern caviomorph superfamilies. By the presence of derived characters in Balsayacuy and Chachapoyamys compared to Canaanimys maquiensis and Cachiyacuy contamanensis from CTA-27 (Contamana, Peru; late middle Eocene), the Balsayacu section may document a time interval slightly younger than CTA-27 (which further yields Chachapoyamys cf. kathetos) and older than those of Santa Rosa and Tarapoto-Shapaja, likely documenting latest middle or early late Eocene times. These low-latitude stem caviomorph faunas provide new insights into the early evolutionary history and paleodiversity of that group immediately before the rise of modern superfamilies.

在过去的几十年中，caviomorph 啮齿动物的古近纪记录大幅增加，它们的进化历史通过它们最早的代表的发现得到了更好的理解，迄今为止记录在秘鲁亚马逊河流域的几个 Pre-Deseadan 地区。我们在此报告在秘鲁 Balsayacu 地区（TAR-55/TAR-55bis、TAR-76 和 TAR-77 地区，圣马丁省）发现了新的鱼形化石。对这种新材料的研究揭示了在这些地方出现了四种腔形类群：Balsayacuy huallagaensis gen。等 sp. 十一月，Chachapoyamys kathetos将军 等 sp. 十一月 和 Caviomorpha gen。等 sp. 插入。1 和 2。它允许对先前描述的标本的分类分配进行修订和细化。前三个分类群具有原始的牙齿图案，因为它表征了秘鲁前 Deseadan 地区（康塔马纳的始新世地区和始新世晚期/渐新世早期的圣罗莎）记录的茎鱼形目。我们在这里支持 Balsayacu 部分的始新世时代，因为完全没有代表现代腔形超家族的形态衍生分类群。与Canaanimys maquiensis和Cachiyacuy contamanensis相比，Balsayacuy和Chachapoyamys中衍生特征的存在来自 CTA-27（秘鲁康塔马纳；中始新世晚期），Balsayacu 剖面可能记录的时间间隔比 CTA-27（这进一步产生Chachapoyamys cf. kathetos）略年轻，并且比 Santa Rosa 和 Tarapoto-Shapaja的时间间隔更旧记录最晚的中晚期始新世时代。这些低纬度干鱼形动物群提供了对现代超家族兴起之前该群体的早期进化历史和古生物多样性的新见解。