Aye Ko Aung

Reevaluation of some ungulate mammals from the Eocene Pondaung Formation, Myanmar

Abstract We reevaluate some fossil specimens of ungulate mammals from the uppermost middle Eocene Pondaung Formation (central Myanmar), describing some new materials. The taxa studied in this paper are Hsanotherium parvum (Ungulata), Asiohomacodon myanmarensis gen. et sp. nov. (Artiodactyla; Dichobunidae; Homacodontinae), Indomeryx (Artiodactyla; Ruminantia), Indolophus guptai (Perissodactyla; Tapiromorpha; Indolophidae), and Ceratomorpha fam., gen. et sp. indet. (Perissodactyla). (1) The lower molars of Hsanotherium show a similarity to those of Gobiohyus pressidens (Artiodactyla; Helohyidae), and its mesiodistally elongated and trilobed dP4 morphology recalls that of artiodactyls and macroscelideans. However, the unique molar and P4 morphologies of Hsanotherium indicate that Hsanotherium cannot confidently be classified into any present ungulate order, although it can be identified as belonging to the Ungulata because of its large, elongated, and posteriorly projecting hypoconulid on M3. (2) The molar size and morphology of Asiohomacodon recall primitive protoreodontine agriochoerids (Oreodontoidea) such as Protoreodon parvus and derived and agriochoerid-like homacodontine dichobunids such as Pentacemylus, both of which occur in Eocene North America. Asiohomacodon is classified not into the Protoreodontinae but into the Homacodontinae because of the lack of molar metastylid. The lower molar morphology of Asiohomacodon also resembles that of an unusual and agriochoerid-like anthracotheriid, Atopotherium, from Eocene Thailand, although the affinity between these two genera cannot be tested because of the lack of the P4 material of Asiohomacodon. (3) The Pondaung Indomeryx consists of large and small species, I. cotteri (including I. pilgrimi) and I. arenae (including I. minus). Dental morphology in each species of the Pondaung Indomeryx indicates relatively high variation, and the two species are not separable based on their dental morphology. Indomeryx shows many primitive characteristics among ruminants and lacks any critical derived features referable to any ruminant family. (4) Indolophus is referable to primitive tapiromorphs in having a somewhat lophodont dentition and in lacking lingual and buccal cingula and molar metaconule, paraconule, and metastylid. It differs from other tapiromorphs in having a smaller parastyle on the upper dentition and a unique P2–4 morphology with large protocone, high and acute preprotocristid, and no postprotocristid. (5) Although the material of the indeterminate ceratomorph is poorly preserved, its preserved tooth is not identical to any other ceratomorph from the Pondaung Formation, indicating an occurrence of an additional ceratomorph species in the Pondaung fauna.

A new anthracotheriid artiodactyl from Myanmar, and the relative ages of the Eocene anthropoid primate-bearing localities of Thailand (Krabi) and Myanmar (Pondaung)

Abstract A fragmentary maxillar of a small anthracotheriid has been discovered in the middle Eocene locality of Kyawdaw in the Pondaung Formation (Myanmar). This specimen represents a primitive new species (Siamotherium pondaungensis, sp. nov.), possibly ancestral to Siamotherium krabiense from the late Eocene of Krabi (Thailand). The occurrence of S. pondaungensis in Myanmar suggests that Krabi is younger than the localities of the Pondaung Formation, and it further supports the role that southern Asia played in the origin and evolution of several groups of mammals.

A NEW GENUS AND SPECIES OF HYAENODONTID CREODONT FROM THE PONDAUNG FORMATION (EOCENE, MYANMAR)

NAOKO EGI1*, PATRICIA A. HOLROYD2, TAKEHISA TSUBAMOTO1, NOBUO SHIGEHARA1, MASANARU TAKAI1, SOE THURA TUN3, AYE KO AUNG4, and AUNG NAING SOE4, 1Primate Research Institute, Kyoto University, Inuyama, Aichi 484-8506 Japan, egi@anthro.zool.kyotou.ac.jp; 2Museum of Paleontology, University of California, Berkeley, California 94720 U.S.A.; 3Department of Geology, University of Yangon, Yangon, Myanmar; 4Department of Geology, Dagon University, Yangon, Myanmar