Isotopic niche modelling of the Pondaung mammal fauna (middle Eocene, Myanmar) shows microhabitat differences. Insights into paleoecology and early anthropoid primate habitats

The late Middle Eocene Pondaung Fm. is a window to understand the environment and ecosystem dynamics of a past greenhouse world and the paleoenvironments where modern mammal clades such as anthropoid primates originated. Previous studies focused on the overall climate and vegetation of this Eocene habitat and provided first evidence for an early monsoon onset before the orogenesis of the Himalayan-Tibetan range. Here, we wanted to investigate how the mammal fauna used this habitat and which different ecological niches and microhabitats they occupied. We analyzed the carbonate fraction of dental enamel of a fossil mammal assemblage from various localities of the Pondaung Fm. in Myanmar. Bayesian niche modelling of the δ¹³C and δ¹⁸O values allowed us to quantify aspects of the ecological core niches occupied by these taxa, to calculate niche overlap and to use these data to infer directional competition potential in this mammal assemblage. Furthermore, comparison of different areas of the Pondaung Fm. revealed two different microhabitats whose distribution is consistent with existing vegetation models. Most primate taxa were found in both described environments, which gives a first indication about their ecological flexibility.

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The different localities where the fossil specimens analyzed in this study have been found can be separated into three areas. Therefore, we wanted to test if the isotopic ratios indicate a difference in environment between them. Visual inspection of the δ¹³C and δ¹⁸O values per area (Figure 3) showed some inter-area differences. The comparison of δ¹³C and δ¹⁸O values from the Bahin and Pangan localities using Wilcox rank sum tests showed no significant difference (p = 1 in both cases). Hence, these two areas will be grouped together for the ecological niche modelling. We then conducted a Wilcox rank sum test, to see if the δ¹³C and δ¹⁸O values were significantly different in the Mogaung area than in the Bahin and Pangan ones. All of these test results showed significant differences (Mogaung—Bahin C: p = 0.001, O: p = 0.001; Mogaung—Pangan C: p = 0.003, O: p = 0.110). Hence, we modelled the ecological niches separately for the mammals from the Mogaung localities.

References

Habinger S. G., Chavasseau O., Ducrocq S., Chaimanee Y., Jaeger J.-J., Sein C., Soe A. N., Stern S., Bocherens H. 2023 – Isotopic niche modelling of the Pondaung mammal fauna (middle Eocene, Myanmar) shows microhabitat differences. Insights into paleoecology and early anthropoid primate habitats – Frontiers in Ecology and Evolution 11:1110331 – https://doi.org/10.3389/fevo.2023.1110331