Abstract In this contribution, we report the discovery of Archaeogaia macachaae gen. et sp. nov., one of the oldest notoungulate recovered from the upper section of Mealla Formation in the Tonco Valley (Northwestern Argentina, Salta Province). The new material consists on a left mandibular fragment with damaged m1 and complete m2-3. Archaeogaia macachaae is characterized by the following combination of features: m1 slightly shorter than m2 and both larger than m3; brachydont molars; talonid mesio-distally shorter than trigonid; metaconid slightly taller than protoconid and distally placed; reduced paraconid in m2; metalophid straight in m2–3, but it runs mesially forming a slightly obtuse angle in the labial edge in m2, whereas it is more transverse in m3; transverse entolophid; mesial cingulid extending from the middle to the lingual face of molars; and distal cingulid connecting the hypoconulid with the mesial face of the entoconid on m2–3. We perform a phylogenetic analysis based on a data matrix composed of 147 craniodental characters and 70 taxa. The analysis yields 6104 most parsimonious trees of 423 steps each. In the strict consensus previously well-supported clades collapse into a polytomy; and Archaeogaia is positioned within the order Notoungulata based on two synapomorphies: a) presence of a transverse entolophid, and b) lower cheek teeth with short mesio-distal protolophid, transverse metalophid and mesio-distal hypolophid slightly convex labially. The former character was recovered as a synapomorphy for Notoungulata in several previous studies. According to the reduced consensus, Archaeogaia occupies different positions within the order; these fluctuating locations could be the result of the presence of plesiomorphic features in the holotype, and the absence of the structures that define the notoungulate clades in which the new taxon is located. The paleomagnetic data indicates that the Mealla Formation was deposited during Chron 27r to the base of Chron 26r (latest Danian-earliest Selandian). In this context, we discuss the finding of Archaeogaia, and the age of Mealla Formation in the South American biochronology.

中文翻译：

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Archaeogaia macacaae gen。等 sp. 11 月，最古老的 Notoungulata Roth 之一，1903 年来自早中期古新世 Mealla 组（阿根廷安第斯山脉中部），对古新世-始新世南美洲生物年代学有深入了解

摘要 在这篇文章中，我们报告了 Archaeogaia macacaae gen 的发现。等 sp. 11 月，是从 Tonco 山谷（阿根廷西北部，萨尔塔省）的 Mealla 组上部发现的最古老的无蹄类动物之一。新材料包括左下颌骨碎片，m1 受损，m2-3 完整。Archaeogaia macacaae 具有以下特征组合：m1 略短于 m2 且均大于 m3；短齿磨牙；爪龙近中远短于三棱；后分生子略高于原分生子并且位于远端；在 m2 中减少 paraconid；在 m2-3 中为直的，但在 m2 中它的唇缘向近中延伸形成一个略微钝角，而在 m3 中它更横向；横向的内蜈蚣；近中扣带从磨牙的中部延伸到舌面；远端 cingulid 将下锥体与 m2-3 上的内锥体的近中面连接起来。我们基于由 147 个颅牙特征和 70 个分类群组成的数据矩阵进行系统发育分析。分析产生了 6104 个最简约的树，每个树有 423 个步骤。在严格的共识中，先前得到良好支持的进化枝会崩溃为多分枝；和 Archaeogaia 位于 Notoungulata 目内基于两个突触：a) 存在横向内足类动物，和 b) 下颊齿具有短的近中远侧原虫、横侧金足类和近中远侧唇类略微凸出的唇部。在之前的几项研究中，前一个字符被恢复为 Notoungulata 的突触。根据减少的共识，Archaeogaia 在命令中占据不同的位置；这些波动的位置可能是由于正模标本中存在拟形特征，并且缺少定义新分类群所在的爪形动物进化枝的结构。古地磁资料表明，Mealla 组沉积于 Chron 27r 至 Chron 26r 底部（最晚达年-最早的 Selandian）。在这种情况下，我们讨论了古生物的发现，以及南美生物年代学中 Mealla 组的年龄。古地磁资料表明，Mealla 组沉积于 Chron 27r 至 Chron 26r 底部（最晚达年—最早的 Selandian）。在这种情况下，我们讨论了古生物的发现，以及南美生物年代学中 Mealla 组的年龄。古地磁资料表明，Mealla 组沉积于 Chron 27r 至 Chron 26r 底部（最晚达年—最早的 Selandian）。在这种情况下，我们讨论了古生物的发现，以及南美生物年代学中 Mealla 组的年龄。