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Evolutionary Ecology of fossil anthropoid primates in Southeast Asia

Subject Area Palaeontology
Term from 2018 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 406582743
 
Final Report Year 2023

Final Report Abstract

Fossil formations of Southeast Asia document a highly dynamic period in mammalian evolution during the Cenozoic. Many clades of modern mammals originated from this biogeographic region or experienced diversification there including early anthropoid primates and pongines. In our project, we characterized the ecological and environmental contexts in which these developments took place, specifically in regard to palaeoseasonality, vegetation structure, diet and niche partitioning. We focused on two fossil mammal faunas from the Central Basin of Myanmar representing two key time periods in the evolutionary history of primates. The middle Eocene Pondaung Fm. (40 Ma) offers a rare opportunity to explore ecosystem dynamics in a greenhouse world not unlike the one predicted as a scenario for our future following the trends of global warming. In this habitat, we find a large number of different early anthropoid primates as well as a diverse herbivorous mammal fauna and a well-diversified guild of creodont carnivores. With our data, we could further proof the existence of a monsoon-like climate even though the orogenesis of the Himalayas was not yet complete and the paleolatitude of the Pondaung Fm. was much closer to the equator than it is today. Although the Pondaung Fm. paleoenvironments are interpreted as deltaic with numerous paleoriver channels, we could not find evidence that any of the herbivorous mammals had an aquatic or a semi-aquatic lifestyle. We could demonstrate that the different localities belonging to the Pondaung Fm. represent two different microhabitats, differentiated by humidity and forest density. At least one genus of early anthropoid, Pondaungia, was found at localities from both microhabitats, hinting towards some degree of ecological flexibility in these primates. With the second mammal assemblage from the late Miocene Irrawaddy Fm. (ca. 9.5 Ma), we addressed open questions regarding the evolutionary ecology of Ponginae in Southeast Asia. Today, there only is one genus, Pongo (the orangutans), whose geographical distribution is highly restricted to the islands of Borneo and Sumatra. From the Miocene to the Pleistocene however, species diversity and geographic range were much more extensive. The Irrawaddy Fm. is an example for the habitat of the sister-group of extant orangutans, Khoratpithecus, represented here by the species Khoratpithecus ayeyarwadyensis. With the stable isotope analysis, we characterized the habitat of this fossil pongine by reconstructing its paleoseasonality, vegetation structure and niche partitioning. We also integrated dental microwear texture analysis to reconstruct paleodietary diversity in the clade. We could show that the dependence on forested habitats in Ponginae was already present in the Miocene. However, Khoratpithecus possibly foraged higher up in the canopy of the forest than orangutans today and likely had a higher diversity of dietary ecologies. Our work on the Miocene representatives of the pongines as well as on a data set of orangutans from the 1890s bridges the gap between palaeontology and conservation ecology and biology working on extant primate faunas and orangutans especially.

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