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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.

Serows and gorals (Bovidae, Caprinae) are emblematic antelopes distributed in Southeast Asia. They all are nearly threaten or vulnerable species nowadays despite having a more widespread distribution during the Pleistocene. Fossils of three native caprine species, i.e., a Sumatran serow Capricornis sumatraensis, Chinese goral Naemorhedus griseus, and Himalayan goral Naemorhedus goral, were recovered from four Pleistocene paleontological and archeological sites in Thailand, namely Pha Bong, Khok Sung, Tham Wiman Nakin, and Tham Lod Rockshelter. To investigate dietary changes of these Southeast Asian serows and gorals through the Quaternary, differences in feeding habits and habitat preferences between the Pleistocene and extant populations were examined using the hypsodonty index (HI) together with the mesowear II method and the dental microwear texture analysis (DMTA). The HI and mesowear-II results showed that Pleistocene and extant caprines were mixed feeders. For the Pleistocene caprine populations, the DMTA results suggested more browsing signals for C. sumatraensis than both Naemorhedus species that were mixed feeders similar to their extant populations. The DMTA demonstrated a considerable dietary overlap among the Pleistocene sympatric caprine populations. The dental microwear results also revealed that the extant C. sumatraensis is a leaf-dominant browser, while the extant N. griseus possibly feeds on seeds or tough food items. These data combined with previous stable carbon isotope analyses reinforce the idea that the restricted ranges of habitats for these extant serow and goral populations have possibly been driven by the Holocene climatic and environmental changes as well as the negative effects of human activities.

Three taxa within the subfamily Caprinae (Himalayan goral Naemorhedus goral, Chinese goral Naemorhedus griseus, and Sumatran serow Capricornis sumatraensis) live in the mountainous upland forests of Southeast Asia, where they are considered as vulnerable or near threatened species. Co-occurrences between these two recognized genera have been documented from some Pleistocene fossil sites in Thailand, suggesting more widely overlapping distribution in the past than today. However, diet and habitat preferences of these Pleistocene and present-day coexisting species have rarely been investigated so far. For the past three decades, stable carbon and oxygen isotope analyses become more commonplace in ecological investigations, allowing us to explore the diets and habitats of ancient and extant animals as well as to reconstruct environmental conditions in the past. We reconstructed diets and habitats of these taxa from five fossil sites in Thailand during the past 400,000 years (from the Middle Pleistocene to the Early Holocene) and from some modern wildlife using the isotopic analysis of carbonate in tooth enamel, in order to test species co-occurrence patterns during the Pleistocene and to examine possible changes of their niche breadths over evolutionary time. Our carbon isotope analysis revealed remarkably different ecological patterns between Naemorhedus and Capricornis. The Pleistocene Sumatran serow has been a greater generalist than both the Himalayan and Chinese gorals that fed on pure C4 or mixed C3 and C4 plants restricted to an open landscape habitat and than its extant population that occupies a closed-canopy forest. This suggests that the habitat contraction of the modern wildlife is likely due to the Holocene climate change and the human impacts on Thai ecosystems. In addition to the loss or reduction of grasslands after the latest Pleistocene when rainforests became dominant and besides the human hunting and predation pressure, the high interspecific competition likely contributed to the extirpation of Himalayan gorals in Thailand. Developing a strategic plan for the future biodiversity conservation, a long-term historical isotope approach allowed us to predict the contrasting habitat suitability, a lowland grassland, for these two threatened goral species as testified by their ecological persistence during the Pleistocene.