New radiometric 40Ar–39Ar dates and faunistic analyses refine evolutionary dynamics of Neogene vertebrate assemblages in southern South America

Abstract

The vertebrate fossil record of the Pampean Region of Argentina occupies an important place in South American vertebrate paleontology. An abundance of localities has long been the main basis for constructing the chronostratigraphical/geochronological scale for the late Neogene–Quaternary of South America, as well as for understanding major patterns of vertebrate evolution, including the Great American Biotic Interchange. However, few independently-derived dates are available for constraining this record. In this contribution, we present new 40Ar/39Ar dates on escorias (likely the product of meteoric impacts) from the Argentinean Atlantic coast and statistically-based biochronological analyses that help to calibrate Late Miocene–Pliocene Pampean faunal successions. For the type areas of the Montehermosan and Chapadmalalan Ages/Stages, our results delimit their age ranges to 4.7–3.7 Ma and ca. 3.74–3.04 Ma, respectively. Additionally, from Buenos Aires Province, dates of 5.17 Ma and 4.33 Ma were recovered for “Huayquerian” and Montehermosan faunas. This information helps to better calibrate important first appearances of allochthonous taxa in South America, including one of the oldest records for procyonids (7.24–5.95 Ma), cricetids (6.95–5.46 Ma), and tayassuids (> 3.74 Ma, oldest high-confidence record). These results also constrain to ca. 3 Ma the last appearances of the autochthonous sparassodonts, as well as terror birds of large/middle body size in South America. South American faunal turnover during the late Neogene, including Late Pliocene extinctions, is interpreted as a consequence of knock-on effects from global climatic changes and initiation of the icehouse climate regime.

Reevaluando El Registro Fósil De Lagostomus Incisus Ameghino, 1888 (Rodentia, Caviomorpha) Del Neógeno Tardío Del Sur De América Del Sur

“…Although most of the units where remains of Lagostomus incisus have been recovered are not dated, many of them have estimated ages based mainly on vertebrate fauna (e.g., Cione & Tonni, 1995;Tomassini et al, 2013;Pardiñas et al, 2017), and recent works have adjusted the age with new radiometric dates (e.g., Prevosti et al 2021). The age of each unit (see Fig.…”

“…The age of the Monte Hermoso Formation has been estimated between 5.28 Ma and 4.5/5.0 Ma (Tomassini et al, 2013), so the Montehermosan Stage/Age (sensu Tomassini et al, 2013) is restricted to the early Pliocene. However, based on statistical analyses (see Prevosti et al, 2021) a new temporal range to this unit has been inferred between 4.741 and 3.728 Ma, placing it in a slightly younger age, in the late early Pliocene. The material recovered from the Monte Hermoso Formation came from upper levels or do not have precise stratigraphic provenance within the unit (see .…”

“…The age of the "Irenean" Fauna has been subject of debate for decades (see Pardiñas et al, 2017 for extensive discussion), and have been recently dated (Prevosti et al, 2021), ending a long lasting controversy. The material of Lagostomus incisus recovered from levels bearing the "Irenean" Fauna come from the Cascada Grande locality , with a probable Montehermosan age (Pardiñas et al, 2017) and a new radiometric date that place it in 4.33 + 0.06 Ma (Prevosti et al, 2021). Ma (Schultz et al, 1998), and recent radiometric dates of level VI (3.74+0.05 Ma) and level X (3.04+0.06 Ma) place the Chapadmalal Formation undoubtedly in the late Pliocene (Prevosti et al, 2021).…”

“…Lagostomus incisus was described by Ameghino (1888) for the Monte Hermoso Formation (early Pliocene, Montehermosan Stage/Age; see Tomassini et al, 2013), along with 'Lagostomus spicatus ' Ameghino, 1888. Later, Ameghino (1908 mentioned a similar species to 'Lagostomus spicatus' in the Chapadmalal Formation (late Pliocene, Chapadmalalan Stage/Age; see Prevosti et al, 2021).…”

“…Until recent works, the precise age of late Neogene sediments of the Pampean area-where Lagostomus incisus has been recorded-rely almost exclusively on biostratigraphic studies (e.g., Cione & Tonni, 1995;Deschamps et al, 2012;Tomassini et al, 2013;Pardiñas et al, 2017), being the Chapadmalal Formation the only dated unit (Schultz et al, 1998). Recently, the sediments bearing the "Irenean" Fauna and the Chapadmalal Formation has been dated with radiometric methods (Prevosti et al, 2021) Jackson et al, 1996). 2, Location map of fossil localities mentioned in the text.…”