The Great American Biotic Interchange (GABI) revisited: a perspective from the stable isotope record of Argentine fossil mammals

MONTALVO, CLAUDIA; KOCH, PAUL; DOMINGO, LAURA; ALBERDI, TERESA; TOMASSINI, RODRIGO

París

Congreso; 5th International Paleontological Congress; 2018

International Palaeontological Association

The South American late Cenozoic fossil record constitutes an exceptional natural laboratory to study mammalian paleoecology in the context of changing biotic and abiotic forces. South America remained largely isolated from other landmasses for more than 50 Ma. First, the presence of emerging land resulted in the early exchange of South American and North American terrestrial taxa at the Late Miocene and then, the permanent establishment of the Isthmus of Panama (~3.1?2.7 Ma), triggered a massive faunal interchange since the end of the Pliocene. This event is known as the Great American Biotic Interchange (GABI). In this study, we investigate the paleoecological response to the GABI of South American and North American fossil mammals through the application of stable isotope techniques. We focused on a long-term fossil record from the Pampean Region (La Pampa and Buenos Aires provinces, Argentina) spanning from ~9 Ma to ~12 Ka. Selecting a single region allows us to evaluate variability on taxa resource and habitat use through time within a same geographical and geomorphological context. Tooth enamel 13C record along with niche assessment point to a major shift in resource use by most of endemic herbivorous taxa (caviomorph rodents, notoungulates, xenarthrans), switching from a pure C3 diet to an intermediate C3-C4 diet at the Late Miocene-Early Pliocene and tracking the expansion of C4 plants in South America. On the contrary litopterns kept a C3-dominated diet throughout the whole studied interval. A flexible dietary behavior shown by North American herbivorous taxa including C4 vegetation (gomphotheres and equids), or a wide range of C3 resources (cervids) may have favored the successful settlement of some immigrant groups in the Pampean area. Bayesian mixing models applied to evaluate predator-prey interactions reveal that endemic Sparassodonta (i.e., Borhyaenoidea) preferred prey from pure C3 environments, whereas North American Carnivora (i.e., Felidae) consumed prey from mixed C3-C4 areas. This study provides the first integral stable isotope record of more than 350 specimens of 11 orders/superorders of Pampean endemic and immigrant mammals. It has revealed as an invaluable proxy to characterize paleoecological traits, including shifts in resource and habitat use throughout the GABI, up to now difficult to assess by other means.