Systematics and phylogeny of middle Miocene Cervidae (Mammalia) from Mae Moh Basin (Thailand) and a paleoenvironmental estimate using enamel isotopy of sympatric herbivore species

ABSTRACT

The primitive deer (subfamily Lagomerycinae) Lagomeryx and Stephanocemas are characterized primarily by their palmate antlers. Two lagomerycines, Lagomeryx manai, sp. nov., and Stephanocemas rucha, are described for the first time from Q and K coal layers of the late middle Miocene (13.4–13.2 Ma) Mae Moh Basin in northern Thailand. A species-level phylogeny of the Ligeromeryx-Lagomeryx clade, based on cranial appendages, reconstructs Lagomeryx manai, n. sp., as a derived species of Lagomeryx, sister group of Lagomeryx complicidens. This study suggests that the large species of Lagomeryx are restricted geographically to Asia and dispersed to Southeast Asia at the latest during late middle Miocene, where they are represented by Lagomeryx manai, n. sp. The paleoenvironmental studies of five Mae Moh mammalian taxa, a cervid (Lagomeryx manai, n. sp.), an indeterminate bovid, a suid (Conohyus thailandicus), a rhinoceros (Gaindatherium sp.), and a proboscidean (Stegolophodon sp.), investigated with stable carbon and oxygen isotope analyses of tooth enamel, indicate that the Mae Moh mammals inhabited a wide range of habitats from woodlands to grasslands in a C3-plant-dominated environment. The new species of Lagomeryx seems to have been living in an open environment, contrary to its European relatives. The serial isotopic samples also support that Mae Moh herbivores probably lived in a low-seasonal climate during the late middle Miocene of northern Thailand.

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ACKNOWLEDGMENTS

We would like to thank C. Wissing from Tübingen University, Germany, for his help in laboratory operations and in preparing the isotopic samples. We are grateful to S. Riffaut for her help in drawing the tooth images, and to X. Valentin for his help in reconstructing the protoantler samples. We are also obliged to M. Rugbumrung from Department of Mineral Resources (DMR), who discovered numerous cervid fossils, for his assistance in the field. This work has been supported by the DMR (Bangkok), La Région Poitou-Charentes, and the University of Poitiers (the ANR-05-BLAN-0235 and ANR-09-BLAN-0238-02-EVAH programs). We thank Electricity Generating Authority Thailand (EGAT) for giving us access to Mae Moh mine and in providing logistic and technical assistance. Finally, we would like to thank J. Theodor, X. Wang, G. E. Rössner, and two anonymous reviewers for their helpful comments on the manuscript.

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Handling editor: Jessica Theodor