Evolutionary Ecology of fossil anthropoid primates in Southeast Asia – EVEPRIMASIA

Two methods have been selected to reach our main goal: the isotopic analyses of the dental enamel (C and O isotopes) and the dental microwear textural analyses (DMTA). These two methods bring precious information about the diet and the habitat of the species.
The analyses have been planned at the scale of the mammalian component of the selected faunas to characterize the ecology of the fossil primates but also their ecosystems and the putative link between the climatic factors and their evolutionary ecology.

-Several articles have been published by the PALEVOPRIM partner of the project in order to further document, clarify the taxonomic status and precise the ecology of some species of the Pondaung fauna. 2 articles concern the anthropoid primates of this fauna. 2 additional articles deal with two Pondaung cetartiodactyls. This work is necessary to obtain reliable paleoecological inferences with the isotopic and microwear methodologies.

-A fieldtrip in the Central Basin of Myanmar and a visit of the collections of the National Museum of Myanmar in Nay Pyi Taw have taken place in February 2020. These actions have permitted us to select and sample enamel fragments and enamel powder of mammalian taxa of the Magway and Pondang faunas for isotopic analyses. Dental silicone molds have been cast for future dental microwear textural analyses (analyses to be performed in Poitiers University). In total, about 90 isotopic samples and 60 dental molds have been done during this mission. To these samples must be added the 200 isotopic samples already available at the beginning of the project.

-All of the isotopic samples have been treated and analyzed in the partner laboraroty of Tübingen University directed by Prof. Hervé Bocherens (DFG partner of the ANR PRCI EVEPRIMASIA project). The analysis of the isotopic data are in progress for the Pondaung fauna. Preliminary results indicate that this fauna was living in an environment with strong climatic seasonality. The isotopic analyses of the Magway fauna yielded important results about the paleocology and paleoenvironments of the ape Khoratpithecus (see next section and section C.4 of the Word document).

-The first results brought by the C and O isotopic proxies have been presented in several international symposia. An article with the isotopic data of the Khoratpithecus-bearing fauna of Magway is being finalized.

-Dental molds of Borneo orangutans (Pongo pygmaeus) from the Selenka collection of the Munich museum (specimens sampled between 1892 and 1896) have been cast in 2021 in the frame of a collobration with a reseacher from this institution (Dr. Anneke van Heteren). In total, about 50 indidviduals have been cast, which will ensure obtaining a statistically significant sampled for the species for the microwear analyses.

- The isotopic analyses of the Khoratpithecus fauna of Magway (about 9 Ma) allow further characterizing the ecological niche of the ape Khoratpithecus. This ape was inhabiting closed habitats, similarly to modern orangutans and other fossil pongines. These data pintpoint to an ecological continuity in throughout the evolutionary history of pongines. Our new isotopic data suggest that Khoratpithecus had an ecological niche that was especially close to that of modern pongines and to that of the fossil ape Sivapithecus.

-The analysis of the microwear data, which will be started very soon (analyses scheduled from mid-september onwards), will refine and complete the paleoecological and paleoenvironmental inferences made with the isotopic data. We expect the two coupled methologies to give us access to a much better understanding of the Magway and Pondaung faunas and to bring decisive pieces of evidence relative to the evolutionary ecology of Khoratpithecus and the basal anthropoids from the Pondaung fauna.

-The dental microwear data of Pongo pygmaeus will soon allow us building a database for this rare species in collections. This database is sufficiently interesting in itself to be published and made available to other researchers. It will also serve as an ideal reference to interpret microwear data about fossil pongines such as Khoratpithecus.

Communications in international symposia :
1. Bocherens, H., Chaimanee, Y., Jaeger, J.-J., Soe, A.N., Sein, C., Chavasseau, O., 2019. Isotopic tracking of the palaeoecology of Late Miocene Ponginae (Khoratpithecus, Sivapithecus), 9th annual meeting of the European Society for the study of Human Evolution (ESHE), Liège.
2. Bocherens, H., Stern, S., Jaeger, J.-J., Chaimanee, Y., Soe, A.N., Sein, C., Chavasseau, O., 2019. Isotopic tracking of large ungulate ecology in Middle Eocene Pondaung Formation (Myanmar), 17th conference of the EAVP, Brussels.
3. Habinger, S., Chavasseau, O., Chaimanee, Y., Jaeger, J.-J., Soe, A.N., Sein, C., Stern, S., Bocherens, H., 2020. Evolutionary ecology of fossil primates in South East Asia. Results of two pilot studies, 2nd Palaeontological Virtual Congress.
4. Habinger, S., Chavasseau, O., Bocherens, H, 2021. Paleoecology of khoratpithecus ayeyarwadyensis. ecological niche modelling using stable isotopes. 18th conference of the EAVP, Benevento.

Articles in international journals (peer-reviewed):

1. Jaeger, J.-J., Chavasseau, O., Lazzari, V., Soe, A.N., Sein, C., Le Maître, A., Shwe, H., Chaimanee, Y., 2019. New Eocene primate from Myanmar shares dental characters with African Eocene crown anthropoids. Nature Commun. 10, 3531.
2. Jaeger, J.-J., Sein, C., Gebo, D.L., Chaimanee, Y., Nyein, M.T., Oo, T.Z., Aung, M.M., Suraprasit, K., Rugbumrung, M., Lazzari, V., Soe, A.N., Chavasseau, O., 2020. Amphipithecine primates are stem anthropoids: cranial and postcranial evidence. Proc. R. Soc. B 287, 20202129.
3. Ducrocq, S., Chaimanee, Y, Soe, A.N., Sein, C., Jaeger, J.-J, Chavasseau, O., 2021. First report of the lower dentition of Siamotherium pondaungensis (Cetartiodactyla, Hippopotamoidea) from the late middle Eocene Pondaung Formation, Myanmar. N. Jb. Geol. Paläont. Abh. 301, 217–228
4. Ducrocq, S., Soe, A.N., Sein, C., Chaimanee, Y., Chavasseau, O., Jaeger, J.-J., sous presse. Neochorlakkia myaingensis, a new Dichobunidae (Mammalia, Cetartiodactyla) from the middle Eocene Pondaung Formation, Myanmar. C. R. Palevol.

During the Cenozoic, Myanmar has been a key area for mammalian evolution, this region having seen the emergence and diversification of several major groups of eutherian mammals such as anthropoid primates as well as ruminant and hippopotamoid cetartiodactyls. While a very rich mammalian diversity has been described from this region, very few studies have focused on paleoecological and paleoenvironmental aspects related to these mammalian communities. Thus, our project aims at characterizing the paleoecology and paleoenvironments of the Cenozoic faunas of Myanmar by using combined approaches of carbon and oxygen isotope biogeochemistry and 3D dental microwear texture analyses on mammalian taxa. We willfocus on the world-famous primate-bearing faunas of the Pondaung and Irrawaddy Formations, which offer the best potential owing to their rich mammalian fossil record and the most challenging questions regarding the evolution of primates in the Central Basin of Myanmar
during the Cenozoic, the evolution of these fossil primates being considered as tightly linked to that of their environments.

The Pondaung Formation has yielded several fossiliferous localities dated from the late Middle Eocene (ca. 40-37 Ma), which delivered more than 50 mammalian species including creodonts, primates, cetartiodactyls, perissodactyls and rodents. The most emblematic groups recovered in
this area are the anthropoid primates, the ruminants and the anthracothere cetartiodactyls, which early evolution is documented in Pondaung. Recent studies have proposed that the Pondaung mammalian communities evolved in a seasonal wetlands landscape under a seasonal climate perhaps representing the earliest evidence of the Asian monsoon. Our studyon the Pondaung mammals will allow us to:
- characterize the environments of Pondaung primates and testing the hypothesis of seasonal wetlands and the alleged climate seasonality presently observed on a single mammal species;
- evaluate if environmental and climatic seasonality has impacted specific groups among the Pondaung community;
- evaluate if Pondaung mammals were dependent to water or, in the contrary, purely terrestrial and forced to change habitat during the wet seasons,
- analyze the ecological structure of the fauna and especially characterizing the niche partitioning among Pondaung mostly dentally poorly-specialized herbivores.

The Miocene to Pleistocene Irrawaddy Formation has long yielded a rich diversity of mammals (proboscideans, rhinocerotid, giraffids, bovids, equids) but has only recently delivered a fauna comprising the hominoid primate Khoratpithecus, a Pongo-related fossil, from the Early Late
Miocene. We will study this unique fauna in order to:
- reconstruct the habitat of Khoratpithecus and the paleoenvironments where it evolved by the
study of its associated fauna;
- test the putative presence of C4 plants in the early late Miocene of Myanmar and compare with the situation in the Siwaliks of Pakistan where the C4 plants became dominant around 9 Ma and caused the extinction of the local hominoid, Sivapithecus (e.g. Nelson 2007);
- investigate the niche-partitioning between the diversified herbivores of the fauna,
- compare the environments of Myanmar Khoratpithecus with those of other Asian hominoids (Sivapithecus in Pakistan, Khoratpithecus from Thailand, Lufengpithecus in China).