The Great American Biotic Interchange revisited: a new perspective from the stable isotope record of Argentine Pampas fossil mammals

Abstract

This study aims at assessing resource and habitat use, niche occupation and trophic interactions from a stable isotope perspective on fossil mammals from the Argentine pampas during the Great American Biotic Interchange (GABI). We present stable isotope data of more than 400 samples belonging to 10 mammalian orders and spanning a temporal range from ~9.5 Ma to ~12 ky. Rodents, notoungulates and pilosians record an increase in the consumption of c 4 plants, whereas litopterns and cingulates show δ 13 c values that remain mostly within a c 3 -dominated diet. Our stable isotope data indicates that the expansion of c 4 vegetation opened up new niche opportunities, probably alleviating resource competition among endemic taxa. Gomphothere, equid and camelid δ 13 c records show a broad variability pointing to consumption of c 3 and mixed c 3 -c 4 vegetation. This flexible dietary behavior may have facilitated the successful settlement of immigrant groups in South America. In the case of carnivorous taxa, Late Miocene pre-GABI endemic sparassodonts consumed prey from C 3 environments, whereas immigrant carnivorans preferred prey from mixed C 3 -c 4 areas. Our research contributes to the study of the GABI from a different perspective as stable isotope records permit to characterize, from a (semi)quantitative standpoint, ecological traits within extinct fauna.Understanding the evolution of mammalian communities throughout the history of Earth, their resource and habitat use, niche occupation and trophic relationships play fundamental roles as these variables determine interaction among species, which ultimately trigger profound changes in community structure leading to modern faunal structure 1 .The Late Cenozoic fossil record of South America provides a unique natural laboratory to investigate faunal response in the context of changing biotic and abiotic forces 2 . Recent works on the tectonism, paleoceanography, paleobiogeography and paleobiology of the Isthmus of Panama have refined our knowledge of its final formation, although not without controversy and sometimes opposing views about its tempo and mode 3 . Despite debates about tectonic vs. ecological barriers to intercontinental faunal exchange, most workers accept that South America was mostly isolated from other continents for more than 50 Ma, from the Late Paleocene until regular terrestrial faunal exchange began following the establishment of the Panama corridor 4,5 .The Great American Biotic Interchange (GABI) occurred in pulses, reflecting intermittent connections due to sea level lowstands and glacial-interglacial climatic dynamics 4,6-8 . The first arrival of North American taxa into South America took place in the Late Miocene (Huayquerian) before the total establishment of the Panama corridor. Herald taxa were procyonids, cricetids and later on, tayassuids. Then, once the land bridge was completed

Comparative isotope ecology of western Amazonian rainforest mammals

“…The calculated δ 13 C diet of Amazonian toxodonts (median δ 13 C diet = −27‰) was found to be lower than modern Amazonian artiodactyls, although still not as negative as the African subcanopy feeders (i.e., δ 13 C diet <−30‰). Although other studies have isotopically characterized Pleistocene taxa at high latitudes in South America ( 49 , 50 ), no isotopic characterization of Pleistocene mammalian communities from closed-canopy rainforests has yet been done because of limited known localities from these habitats, where plants with δ 13 C <−30‰ are present and may have been consumed by recently extinct herbivore lineages, as is observed in equatorial Africa today. Isotopic characterization of the Pleistocene Amazonian mammalian community also could better inform understanding of the influence of the extinct megafauna on the realized niches of modern Amazonian mammals by revealing if surviving lineages shifted or expanded their feeding ecologies (and isotope niche occupation) after the extirpation of those species from the ecosystem.…”

: The sloths Scelidotheriinae (Xenarthra, Folivora): taxonomy, biocronology, and biogeography

“…De lo expuesto, se desprende que en Argentina, y más precisamente en la región Pampeana durante el Mioceno tardío-Pleistoceno, se registra la mayor diversidad específica de perezosos Scelidotheriinae, probablemente estimulado por los siguientes factores: a) predominio de ambientes abiertos durante en el Mioceno tardío-Plioceno (Ortiz-Jaureguizar & Cladera, 2006); b) aumento en el consumo de plantas C4, lo que sugiere que la expansión de la vegetación C4 abrió nuevas oportunidades de nicho, y así aliviar la competencia por los recursos entre los taxones endémicos, durante el Mioceno tardío-Pleistoceno (ca. 9 Ma-12 ka) de la región Pampeana de Argentina (Domingo et al, 2020).…”

Gregariousness in the giant sloth Lestodon (Xenarthra): multi-proxy approach of a bonebed from the Last Maximum Glacial of Argentine Pampas

“…Tooth enamel was selected for notoungulates, perissodactyls, artiodactyls, proboscideans, and carnivorans, whereas orthodentine was used in the case of folivorans ( Supplementary Tables S2 and S4). Sampling and technical protocols related to the stable isotope analysis of these samples are detailed in Domingo et al 71 .…”

“…Although speculative, it could have been adopted or have been relevant during the Pleistocene in response to: (1) the occurrence of several glacial-interglacial cycles, which involved continuous and pronounced climatic and environmental changes 4,64 , and the consequent loss of habitats and/or temporal lack of resources; and (2) the impact linked with the most important pulses of the Great American Biotic Interchange. This event implied, on the one hand, the arrival of several herbivorous large and megamammals that would have generated competition for resources and habitats 70,71 . On the other hand, the interaction with new predators; isotopic analyses suggest that L. armatus was a probable prey of the carnivores Smilodon populator (present at Playa del Barco) and Protocyon troglodytes 71,72 .…”

“…This event implied, on the one hand, the arrival of several herbivorous large and megamammals that would have generated competition for resources and habitats 70,71 . On the other hand, the interaction with new predators; isotopic analyses suggest that L. armatus was a probable prey of the carnivores Smilodon populator (present at Playa del Barco) and Protocyon troglodytes 71,72 .…”