Updated knowledge on the Notoungulata (Mammalia) from the late Miocene Cerro Azul Formation, La Pampa Province, Argentina

We describe new remains of notoungulates from the Cerro Azul Formation (late Miocene) in La Pampa Province and reassign others previously studied, helping to precise the taxonomic diversity of 25 fossiliferous localities of this formation. Geomorphological context previously described for the area provides data to place some localities in a temporal sequence. The following Notoungulata are recognised: <i>Protypotherium minutum</i> (Interatheriidae), <i>Paedotherium minor, Tremacyllus impressus, Hemihegetotherium achataleptum, H. torresi</i>, and <i>Hemihegetotherium</i> sp. (Hegetotheriidae), <i>Typotheriopsis silveyrai, T. chasicoensis</i>, and <i>Pseudotypotherium subinsigne</i> (Mesotheriidae), and <i>Pisanodon nazari, Hemixotodon chasicoensis</i>, and cf. <i>Stenotephanos plicidens</i> (Toxodontidae). This study allows adding new localities to the biochronological sequence previously proposed based on the evolutionary pattern of the octodontoid rodents. Chasicoan and early Huayquerian (as herein considered) faunal assemblages present higher diversity of notoungulates than those assigned to late Huayquerian. Some localities lack a representation of taxa significant enough to precise their biochronological position within the late Miocene. The difference in the notoungulates representation along the Chasicoan–Huayquerian ages may be due to climatic changes that affected the centre of Argentina from late Miocene to early Pliocene.

本研究记述了产自拉潘帕省（La Pampa Province）塞罗阿苏尔组（Cerro Azul Formation，晚中新世（late Miocene））的南方有蹄目（Notoungulata）新化石材料，并对此前已研究的其他化石材料进行了重新分类厘定，可为明确该组25个含化石产地的分类多样性提供支撑。该区域已有的地貌背景研究数据，可为部分产地构建时间序列提供依据。本次研究确认的南方有蹄目类群如下：间齿兽科（Interatheriidae）的*Protypotherium minutum*（小原前兽）、赫格托兽科（Hegetotheriidae）的*Paedotherium minor*（小幼兽）、*Tremacyllus impressus*（壮丽震兽）、*Hemihegetotherium achataleptum*（纤细半赫格托兽）、*H. torresi*（托雷斯半赫格托兽）以及*Hemihegetotherium* sp.（半赫格托兽未定种）；中磨齿兽科（Mesotheriidae）的*Typotheriopsis silveyrai*（西尔维拉拟磨齿兽）、*T. chasicoensis*（查西科拟磨齿兽）以及*Pseudotypotherium subinsigne*（亚显假磨齿兽）；箭齿兽科（Toxodontidae）的*Pisanodon nazari*（纳扎里皮萨诺兽）、*Hemixotodon chasicoensis*（查西科半异齿兽）以及cf. *Stenotephanos plicidens*（褶齿狭齿兽相似种）。本研究可为此前基于八齿鼠类（octodontoid rodents）啮齿动物演化模式建立的生物年代序列补充新的产地数据。查西科期（Chasicoan）与早期瓦基里安期（本文所界定的）的动物群组合，其南方有蹄类多样性高于划归晚瓦基里安期的动物群组合。部分产地的类群代表性不足，难以准确界定其在晚中新世地层中的生物年代学位置。查西科期至瓦基里安期的南方有蹄类记录差异，可能源于晚中新世至上新世（Pliocene）早期影响阿根廷中部的气候变化。