Paleoenvironment and paleoecology associated with the early phase of the Great American Biotic Interchange based on stable isotope analysis of fossil mammals and new U-Pb ages from the Pampas of Argentina
By: Dánae Sanz-Pérez, Claudia I. Montalvo, Adriana E. Mehl, Rodrigo L. Tomassini, Manuel Hernández Fernández, Laura Domingo
Summarized by: Sophia Licata is an environmental science and geology double major, who has also taken on a minor in biology at Binghamton University (SUNY). She is currently a senior at the university and plans to attend graduate school to study geological sciences. After obtaining her degree, she plans on pursuing environmental consulting as a career. In her free time, she loves playing volleyball with friends, journaling, and spending time outside.
What data was used? Stable isotope data was collected from different fossil mammalian species, including rodents, anteaters, rhinoceroses, camels, and capybaras from Central Argentina during different parts of the Neogene Period (23.03 – 2.58 million years ago (Mya)). Samples were collected from two locations: the Cerro La Bota location and the Arroyo Chasicó location. Zircon mineral samples from these areas were also collected to obtain radiometric ages of the rocks.
What was the hypothesis being tested? By studying the stable isotope analysis of these mammalian species during the Neogene in Central Argentina, it is possible to gain a better understanding of climatic changes that occurred based on the presence of C3 and C4 plants (C3 and C4 have different photosynthetic pathways, which are indicative of the climatic conditions of their environment. C3 plants are indicative of temperate climates with regular precipitation. C4 plants are indicative of more arid climates that are warmer with little precipitation. In this study, different terms are used to identify geologic stages and ages: “Chasicoan” refers to the Early Miocene (23-16 Mya), “Huayquerian” refers to the Late Miocene – Early Pliocene (11.6-3.6 Mya), and “Montehermosan” refers to the Early Pliocene alone (5.3-3.6 Mya). By identifying the diets of mammalian species during these times, and obtaining the abundances of C3 and C4 plants present then, better conclusions can be drawn about the paleoenvironment and paleoclimate of Central Argentina during the Neogene.
Methods: U-Pb dating of zircons, which come from sediment that has been eroded and weathered from pre-existing rocks, took place at the LA.TE. Andes laboratory in Argentina. Uranium-238/Lead-206 and Uranium-238/Lead-207 radiometric dating was performed to determine and confirm the maximum and minimum depositional age range of the deposits being studied to ensure that the rocks and fossils being examined are within the Neogene Period. When studying mammals at the order and genus levels, the stable isotope data obtained specifically focused on carbon-13 and oxygen-18 isotopes, and the ratios of the isotopes that were present in the carbonates and phosphates found in tooth enamel samples of various mammals. The ratios of carbon and oxygen isotope allow us to determine what kinds of plants were part of their diets (either C3, C4, or a mix of both). This information provides insight into the presence of different plant species, especially if a region was dominated by C3 or C4 plants, by the amount and types of oxygen and carbon isotopes that were present in the environment at the time.
Results: After obtaining information about the presence of carbon isotopes in mammals, there is strong evidence that taxa had mixed C3 and C4 diets in the Chasicoan Stage (the earliest), C3 diets in the Huayquerian Stage, and an increase in C4 diets in the Huayquerian-Montehermosan Stages (the latest). More simply put, there seems to have been a change from C3 plant presence in diets to C4 plants, which may indicate changes in climatic conditions through the studied time interval. In the Huayquerian Stage, where C3 plants dominate more, it can be assumed that there were cooler temperatures with generally moderate amounts of precipitation. This would be different from the Huayquerian-Montehermosan Stage where C4 plants seem to dominate. This would suggest that temperatures had become warmer and precipitation levels have decreased.
Why is this study important? This study is important because it provides detailed insight to the past climate and environmental conditions in Argentina during the Neogene. By comparing carbon and oxygen isotopes, it allows us to understand the temperature and precipitation conditions of the region based on which isotopes are more concentrated in the samples.
Broader implications beyond this study: Studying the diets of different species of different time periods can tell us about the paleoenvironment and paleoclimate. Comparisons can be made about the conditions of the paleoclimate based on what types of plants and fauna were present at the time, like the presence of C3 and C4 plants. Understanding the paleoclimate of this region can help to understand current trends in climate. When the climate in a region changes rapidly, it can be difficult for species, especially mammals, to evolve quickly enough to adapt to a new environment.
Citation: Sanz-Pérez, D., Montalvo, C. I., Mehl, A. E., Tomassini, R. L., Fernández, M. H., & Domingo, L. (2023, November 26). Paleoenvironment and paleoecology associated with the early phases of the Great American Biotic Interchange based on stable isotope analysis of fossil mammals and new U–Pb ages from the Pampas of Argentina. Retrieved September 10, 2024,.