Studies focused on deciduous dentition, ontogenetic series, and tooth eruption and replacement patterns in fossil mammals have lately increased due to the recognized taxonomic and phylogenetic weight of these aspects. A study of the deciduous and permanent dentition of Interatherium and Protypotherium (Interatheriinae) is presented, based mainly on unpublished materials. Deciduous cheek teeth are brachydont and placed covering the apex of the respective permanent tooth; in addition, some morphological and metrical differences are observed along the crown height. Five dental ontogenetic stages are distinguished among the juvenile specimens on the basis of the degree of wear, the replacement of the deciduous premolars, and the eruption of the molars. The crown height and the wear degree of different Interatheriinae taxa show: (1) eruption pattern of molars in an anterior–posterior direction (M/m1 to M/m3); (2) pattern of replacement of deciduous premolars and eruption of permanent premolars in a posterior–anterior direction (dP/dp4 to dP/dp2 and P/p4 to P/p2); and (3) eruption of M/m3 before the replacement of dP/dp4. Results allow evaluating the diagnostic dental characteristics used to describe some interatheriines, as well as reinterpreting some taxonomic assumptions: the holotype of Protypotherium diversidens Ameghino, 1891 is recognized as a juvenile of another species of the genus, and the species is not validated, considering it as Protypotherium sp.; the holotype of Eudiastatus lingulatus Ameghino, 1891 falls in the variability of Protypotherium, becoming P. lingulatus new combination, tentatively maintaining the species and implying the synonymy between Eudiastatus and Protypotherium; and the holotype of Eopachyrucos ranchoverdensis Reguero, Ubilla, and Perea, 2003 is reinterpreted as bearing deciduous premolars.

中文翻译：

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Interatheriinae（Notoungulata，Interatheriidae）的乳牙列和牙齿萌出序列：对该组系统学的影响

由于这些方面公认的分类学和系统发育权重，最近对化石哺乳动物的乳牙列、个体发育系列以及牙齿萌出和替换模式的研究有所增加。乳牙和恒牙列的研究鹌鹑和原兽(Interatheriinae) 主要基于未发表的材料。乳颊牙是短齿，并覆盖相应恒牙的根尖；此外，沿冠高观察到一些形态和度量差异。根据磨损程度、落叶前磨牙的更换和磨牙的萌出，在幼年标本中区分了五个牙齿个体发育阶段。不同齿间类群的冠高和磨损程度表现：（1）磨牙前后方向萌出模式（M/m1～M/m3）；(2) 乳前磨牙替换和永久性前磨牙在前后方向萌出的模式（dP/dp4 到 dP/dp2 和 P/p4 到 P/p2）；(3) dP/dp4置换前M/m3的喷发。异种原菌Ameghino, 1891 被认为是该属另一个种的幼体，该种未被验证，认为它是原兽sp.; 的正模舌形虫Ameghino，1891 年落入可变性原兽， 变得P. lingulatus新的组合，暂时保持物种并暗示之间的同义词Eudiastatus和原兽; 和正模毛茛Reguero、Ubilla 和 Perea，2003 年被重新解释为带有落叶前磨牙。