First report of snakes (Serpentes) from the Late Middle Eocene Pondaung Formation, Myanmar

Abstract

Department of Anthropology, University of Iowa, Iowa City, IA 52242, USAThe reptile fauna of the Eocene Pondaung Formation of central My-anmar (Fig. 1) has received little attention compared to its well-knownmammalian fauna (e.g., Colbert, 1938; Tsubamoto et al., 2000). In priorreports, Buffetaut (1978) described indeterminate crocodylians and dy-rosaurids. Hutchison et al. (in press) described carettochelyid, trionychid,testudinoid, and pelomedusoid turtles from the formation. They addi-tionally noted the presence of agamid lizards, a pristichampsine croco-dilian, and snakes. The snakes are described here.The occurrence of snakes in the Pondaung Formation is significantbecause the fossil history of Paleogene South Asian snakes has histori-cally been under studied relative to the North American and Europeanrecords (e.g., Rage, 1984; Szyndlar, 1984; Holman, 2000), despite hypoth-eses predicting the region as the origin of extant clades (e.g., Underwoodand Stimson, 1990; Rage et al., 1992). The South Asian record consistsprimarily of marine palaeophiid taxa as well as terrestrial/terrigenousspecimens referred to Boidae (Boinae + Erycinae, Table 1). The onlyderived snakes from the South Asian Paleogene are six colubrid verte-brae from the late Eocene Krabi Basin of Thailand (Rage et al., 1992)and a single vertebra referred to Colubroidea (possibly Colubridae) fromthe early Eocene of India (Rage et al., 2003). The absence of coevalcolubroids elsewhere (Rage, 1988), combined with the occurrence of theKrabi Basin record, led Rage et al. (1992) to conclude that Asia repre-sents the center of origin for Colubridae, the most speciose and diverseextant snake clade.The Pondaung snake record consists of two specimens derived fromterrestrial sediments occurring in the upper 100+ meters of the otherwisemarine Pondaung Formation as it crops out to the west and northwest ofMogaung village, Myaing Township, central Myanmar (Fig. 1). Thesnake localities are interpreted as swale-fills and/or paleosols depositedin an ancient floodplain (Soe et al., 2002; see also Ciochon and Gunnell,2002, and Gunnell et al., 2002 for more detailed discussions of the lithol-ogy and stratigraphy of these localities). Traditionally, the age of thePondaung fauna was considered to be late Eocene (e.g., Pilgrim, 1928;Bender, 1983); however, Holroyd and Ciochon (1994) concluded that thePondaung fauna is latest middle Eocene (Bartonian) in age and broadlycontemporaneous with Asian faunas assigned to the SharamurunianLand Mammal Age, a finding confirmed by fission-track dates of 37.2 ±1.3 Ma (Tsubamoto et al., 2002). These findings indicate that thePondaung fauna is slightly older than the Krabi Basin record, which hasbeen dated between 33.54 and 34.65 Ma in age based on paleomagneticcorrelations (Benammi et al., 2001).Here we describe the Pondaung snakes and discuss their relativeimplications for paleoecology, divergence timings, and biogeographichistories. We refrain from erecting new taxa for the Pondaung speci-mens because the record is limited to just the two elements and neitheris complete. Additional material will be necessary to determine wheth-er or not the Pondaung record represents new, distinct taxa, or indi-vidual or intracolumnar variants of previously known South Asiansnakes.