The Late Miocene mammals from the Humahuaca Basin (northwestern Argentina) provide new data on the initial stages of the Great American Biotic Interchange.

CANDELA, A.M.; ABELLO, M; REGUERO, M. A; GARCÍA ESPONDA, C.; PARDIÑAS, U. F. J.; ZURITA, A.E.; PUJOS, F.; MIÑO BOILINI, A. R.; QUIÑONES, S.I; GALLI, C.; LUNA, C.; VOGLINO, D.; DE LOS REYES, M.; CUARANTA, P.; ESCAMILLA, J.

JUJUY

Jornada; XXXIV JORNADAS ARGENTINAS DE MASTOZOOLOGÍA; 2023

In this contribution, we describe new Late Miocene mammalian specimens from the Maimará Formation(Upper Miocene to Lower Pliocene) exposed at Humahuaca Basin (23°–24°S), northwestern Argentina (NWA),and analyse their taxonomy and relevance for our understanding of the initial stages ofthe Great AmericanBiotic Interchange (GABI). The new studied specimens from the Maimará Formation are housed at the Institutode Geología y Minería (UNJu), Jujuy Province. The stratigraphic and geochronologic control of the studiedspecimens indicates a time window of c. 6.6–5.8 Ma. These data are crucial for establishing the oldest recordsof two emblematic groups the Holarctic immigrants of the GABI, the “heralds” of the GABI. The first record ofcricetid rodents (assigned to Genus and species indet. of Sigmodontinae and represented by mandibular andmaxillary fragments with teeth) from the Maimará Formation is reported. Moreover, with an age of c. 6 Ma it isthe first appearance datum (FAD) of these rodents in South America. The age of the procyonid Cyonasuarecorded in this unit is estimated between c. 6.6 and c. 6.4 Ma. The record of procyonids and cricetids in thesame continuous sedimentary sequence suggests that the time interval between the dispersion of both groupsinto the continent during GABI was c. 1 Ma. Among autochthonous mammals from the Maimará Formation, thefirst records of litopterns (assigned to the macrauchenid cf. Windhausenia delacroixi, represented by a partialproximal end of tibia), chlamyphorid (referred to the species Doellotatus chapadmalensis and Macrochorobatesscalabrinii, both represented by isolated osteoderms) and mylodontine xenarthrans (referred to cf.Pleuroestodon, represented by a lower molariform), and caviomorph rodents (including new species ofOctodontidae and Caviidae, represented by mandibular and maxillary fragments with teeth) are described.FADs of immigrant and autochthonous mammals in NWA suggest a major faunal turnover during GABI at theMessinian, probably linked to global climatic changes and the tectonic activity that affected the HumahuacaBasin at that time. Hypsodonty, a dominant feature among Maimaran mammals, may be related to a landscapestrongly influenced by the Andean uplift.