Litopterna (Mammalia) from the Santa Cruz Formation (Early-Middle Miocene), Río Chalía, Patagonia, Argentina

The southern margin of the Río Chalía valley (also known as Sehuen or Shehuen), Province of Santa Cruz, Argentina, offers excellent outcrops of the Early-Middle Miocene Santa Cruz Formation (SCF). However, the information about the faunal content of these levels is scarce due to insufficient prospection. This contribution reports Litopterna specimens collected in 2018 and 2019 from six localities on the southern margin of the Río Chalía valley, spanning a distance of ~30 km. Twenty-one specimens were collected, the majority belonging to Proterotheriidae (18), and three Macraucheniidae. These specimens include mandibular fragments, maxillae, and postcranial elements. Among Proterotheriidae, Tetramerorhinus lucarius, Te. cingulatum, Thoatherium minusculum, Diadiaphorus majusculus, Anisolophus australis, and A. floweri were identified, while the Macraucheniidae record corresponds to Theosodon sp. The taxa recorded in the Río Chalía area align with those recently reported for the SCF in other localities of the province, such as the Atlantic coast between Monte León and Río Gallegos, Río Santa Cruz, and Lago Posadas, as well as other sites across the extensive distribution of the SCF. These recent collections, with well-documented geographic and altitudinal reference, are valuable for verifying Ameghino’s original descriptions and revisiting Santacrucian taxa.