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We describe three new Toxodontidae (Notoungulata) remains from Mendoza Province, west-central Argentina. One is a new mandible (IANIGLA-PV 993) collected at Huayquerías del Este, from the Huayquerías Formation (Late Miocene-earliest Pliocene). This finding adds to two other unpublished specimens from the area stored in old collections. MCNAM-PV 113 is a skull fragment from Huayquerías de San Carlos, lacking exact origin data, and MACN PV 14854 corresponds to associated upper and lower teeth from the so-called Bajada Grande locality, in Huayquerías del Este, from levels now assigned to the Bajada Grande Formation (Late Pliocene-Pleistocene). IANIGLA-PV 993 and MCNAM-PV 113 belong to Xotodon major. This species was described in 1914 based on cranial remains likely from levels now assigned to the Tunuyán Formation. Slight differences between IANIGLA-PV 993 and the holotype of X. major are attributable to intraspecific variation and their ontogenetic stage: smoother anteroventral mandibular angle; ascending ramus with blunt crest between the fossae for the zygomaticomandibularis and masseteric muscles; and tooth features (e.g., p4 with deeper grooves and slightly shorter teeth) that relate to a lesser wear degree. MCNAM-PV 113 shows nasals and upper teeth comparable with the holotype, although teeth are slightly less compressed. The temporal gap between levels yielding the holotype and IANIGLA-PV 993 is not reflected by our taxonomical interpretation. Finally, the specimen MACN PV 14854 is identified as Toxodon chapalmalensis, based upon its similarities with specimens from the Chapadmalal area, Buenos Aires Province, showing a correspondence with the Chapadmalalan Stage/Age of the Pampean Region. [ABSTRACT FROM AUTHOR]

We revise the mammal fossils from the Fray Bentos Formation previously assigned to Notoungulata, as well as some new remains recovered from levels cropping out in Corrientes Province (Argentina). In some cases, previous determinations have been completed to the species level, but others have been substantially modified, identifying different families. At present, identified taxa are: "Prohegetotherium" schiaffinoi (Hegetotheriidae), an undetermined interatheriid that is hypothesized as representing the upper teeth of Eopachyrucos ranchoverdensis, and Argyrohyrax proavus (Interatheriidae), cf. Archaeohyrax suniensis (Archaeohyracidae), cf. Mendozahippus fierensis ("Notohippidae"), a Leontiniidae indet., and some undetermined Notoungulata. The presence of Leontiniidae is based on the specimen CTES-PZ 7871, but those previously assigned to this family are herein discarded as such and reinterpreted (notohippid and undetermined taxon). The Mesotheriidae are discarded among the revised materials, but they are present in the Fray Bentos Formation in Corrientes Province with Trachytherus spegazzinianus (= Ameghinotherium curuzucuatiense). The revised sample presents affinities with the fauna from the type locality of the Fray Bentos Formation, in Uruguay, and the Deseadan assemblages from Quebrada Fiera (Mendoza Province, Argentina), Patagonia (Argentina), and Salla (Bolivia). These similarities are important from a paleobiogeographic point of view, especially by the recognition of cf. M. fierensis, a species only known from Mendoza up to now. Only the finding of new material from Fray Bentos Formation in Corrientes Province will allow us to corroborate these tentative determinations and a possible eastward extension of up-to-now exclusive taxa from Quebrada Fiera. [ABSTRACT FROM AUTHOR]