Chit Sein

Late Middle Eocene primate from Myanmar and the initial anthropoid colonization of Africa

Reconstructing the origin and early evolutionary history of anthropoid primates (monkeys, apes, and humans) is a current focus of paleoprimatology. Although earlier hypotheses frequently supported an African origin for anthropoids, recent discoveries of older and phylogenetically more basal fossils in China and Myanmar indicate that the group originated in Asia. Given the Oligocene-Recent history of African anthropoids, the colonization of Africa by early anthropoids hailing from Asia was a decisive event in primate evolution. However, the fossil record has so far failed to constrain the nature and timing of this pivotal event. Here we describe a fossil primate from the late middle Eocene Pondaung Formation of Myanmar, Afrasia djijidae gen. et sp. nov., that is remarkably similar to, yet dentally more primitive than, the roughly contemporaneous North African anthropoid Afrotarsius. Phylogenetic analysis suggests that Afrasia and Afrotarsius are sister taxa within a basal anthropoid clade designated as the infraorder Eosimiiformes. Current knowledge of eosimiiform relationships and their distribution through space and time suggests that members of this clade dispersed from Asia to Africa sometime during the middle Eocene, shortly before their first appearance in the African fossil record. Crown anthropoids and their nearest fossil relatives do not appear to be specially related to Afrotarsius, suggesting one or more additional episodes of dispersal from Asia to Africa. Hystricognathous rodents, anthracotheres, and possibly other Asian mammal groups seem to have colonized Africa at roughly the same time or shortly after anthropoids gained their first toehold there.

Talar Morphology, Phylogenetic Affinities, and Locomotor Adaptation of a Large-Bodied Amphipithecid Primate From the Late Middle Eocene of Myanmar

A well-preserved fossil talus [National Museum of Myanmar Primates (NMMP) 82] of a large-bodied primate is described from the late middle Eocene Pondaung Formation of central Myanmar. The specimen was collected at Thandaung Kyitchaung, a well-known amphipithecid primate-bearing locality near the village of Mogaung. NMMP 82 adds to a meager but growing sample of postcranial remains documenting the large-bodied primates of the Pondaung Formation. This new talus exhibits a suite of features that resemble conditions found in living and fossil haplorhine primates, notably anthropoids. As such, the phylogenetic signal deriving from the morphology of NMMP 82 conflicts with that provided by NMMP 20, a partial skeleton (including a fragmentary calcaneus) of a second large-bodied Pondaung primate showing undoubted adapiform affinities. Analysis subtalar joint compatibility in a hypothetical NMMP 82/NMMP 20 combination (talus/calcaneus) reveals a substantial degree of functional mismatch between these two tarsal bones. The functional incongruence in subtalar joint morphology between NMMP 20 and NMMP 82 is consistent with the seemingly divergent phylogenetic affinities of these specimens, indicating that two higher level taxa of relatively large-bodied primates are documented in the Pondaung Formation. On the basis of its size and morphology, we refer the NMMP 82 talus to the large-bodied amphipithecid Pondaungia. The occurrence of anthropoid-like tali in the Pondaung Formation obviates the need to invoke homoplasy to explain the shared, derived dental characters that are common to amphipithecids and undoubted anthropoids. Functionally, the NMMP 82 talus appears to have pertained to a primate that is engaged in active quadrupedalism in an arboreal environment along broad and subhorizontal branches. The primate taxon represented by NMMP 82 was capable of climbing and leaping, although it was not particularly specialized for either of these activities.

A RHINOCEROTID PERISSODACTYL FROM THE LATE MIDDLE EOCENE PONDAUNG FORMATION, MYANMAR

PATRICIA A. HOLROYD, TAKEHISA TSUBAMOTO, NAOKO EGI, RUSSELL L. CIOCHON, MASANARU TAKAI, SOE THURA TUN, CHIT SEIN, and GREGG F. GUNNELL, Museum of Paleontology, University of California, Berkeley, California 94720 U.S.A. pholroyd@berkeley.edu; Primate Research Institute, Kyoto University, Inuyama, Aichi 484-8506 Japan; Laboratory of Physical Anthropology, Graduate School of Science, Kyoto University, Kyoto 606-8502 Japan; Departments of Anthropology and Pediatric Dentistry, University of Iowa, Iowa City, Iowa 52242 U.S.A; Department of Geology, University of Yangon, Yangon, Myanmar; Museum of Paleontology, University of Michigan, Ann Arbor, Michigan 48109 U.S.A

Uniquely derived upper molar morphology of Eocene Amphipithecidae (Primates: Anthropoidea): Homology and phylogeny

The extinct Southeast Asian primate family Amphipithecidae is regularly cited in discussions of anthropoid origins, but its phylogenetic position remains controversial. In part, the lack of consensus regarding amphipithecid relationships can be attributed to uncertainty regarding the homology of upper molar structures in this group. Here, we describe a virtually pristine upper molar of Pondaungia cotteri from the late middle Eocene Pondaung Formation of Myanmar, which is the first example of a relatively unworn and well-preserved amphipithecid upper molar ever recovered. The distolingual upper molar cusp in this new specimen of Pondaungia appears to be a lingually displaced and enlarged metaconule, rather than a hypocone or pseudohypocone as previous workers have thought. Reassessment of the upper molar morphology of other amphipithecids and putative amphipithecids reveals a very similar pattern in Siamopithecus, Myanmarpithecus and Ganlea, all of which are interpreted as having upper molars showing many of the same derived features apparent in Pondaungia. In contrast, the upper molar morphology of Bugtipithecus diverges radically from that of undoubted amphipithecids, and the latter taxon is excluded from Amphipithecidae on this basis. Phylogenetic analyses of several character-taxon matrices culled from the recent literature and updated to reflect the new information on amphipithecid upper molar morphology yield similar results. Consensus tree topologies derived from these analyses support amphipithecid monophyly and stable relationships within Amphipithecidae. Amphipithecids appear to be stem members of the anthropoid clade.

Additional materials of Myanmarpithecus yarshensis (Amphipithecidae, Primates) from the middle Eocene Pondaung Formation

Myanmarpithecus yarshensis is an amphipithecid primate from the middle Eocene Pondaung Formation in Myanmar. It was previously known based on maxillary fragments with P4–M3 and mandibular fragments with C–P3 and M2–3. This study reports new materials for the genus, including a humeral head fragment, a lingual fragment of the right M2, a lingual fragment of the right M3, and a left I1. These new materials were collected from approximately the same point, and likely belonged to the same individual. The upper molar morphology and size of the new materials show similarity to those of the type specimen, indicating that the new materials can be assigned to M. yarshensis. The humeral head is the first postcranial element that is associated with dental materials for amphipithecids. The morphological similarity between the previously reported larger humerus and this specimen confirms the assignment of the former specimen to Amphipithecidae and suggests common locomotor adaptations in the family. The upper central incisor is large relative to the molar fragments, but is within the variation among extant platyrrhines. The tooth is spatulate-shaped and high crowned, and lacks the mesial process, indicating similarity to I1 of haplorhines and clear differences from that of adapoids. It has been suggested that amphipithecids, including Myanmarpithecus, have affinities with notharctine adapoids, but the morphology of I1 does not support the notharctine hypothesis of the Amphipithecidae.

New remains of Siamotherium pondaungensis (Cetartiodactyla, Hippopotamoidea) from the Eocene of Pondaung, Myanmar: Paleoecologic and phylogenetic implications

ABSTRACT We describe an exceptionally well preserved skull of a small anthracothere from the late middle Eocene of the Pondaung Formation that can be confidently attributed to Siamotherium pondaungensis, a species that was first diagnosed on the basis of a fragmentary maxilla preserving two upper molars. The new material confirms that Siamotherium pondaungensis is an anthracothere and not a helohyid as repeatedly suggested. According to its dentition and skull structure, Siamotherium pondaungensis was most likely a terrestrial, open-forest animal with an omnivorous diet that showed no significant adaptation to folivory. A phylogenetic analysis that includes both species of Siamotherium confirms their basal position within the Hippopotamoidea.

Chapter 9 Review of the investigation of primate fossils in Myanmar

Since the discovery of fossil primates in the early twentieth century, the later Eocene Pondaung Formation in central Myanmar has attracted the attention from many palaeoprimatologists (Fig. 9.1). There were two large-bodied primates, Pondaungia cotteri and Amphipithecus mogaungensis (Fig. 9.2), known from two localities (Pangan and Mogaung) in the Pondaung area (Fig. 9.3), and many researchers have argued over the phylogenetic position of these two monkeys, that is, whether or not the Pondaung primates are anthropoids, higher primates which includes the clades of New and Old World monkeys, apes and humans. However, due to the scarcity of the fossil specimens, the controversy concerning the phylogenetic position of the Pondaung primates was not resolved until the 1970s. Some authorities believed they are primitive anthropoids, while others regarded them as adapiforms or non-primate, such as condylarthrans (Pilgrim 1927; Colbert 1937; von Koenigswald 1965; Szalay 1970; Simons 1971; Szalay & Delson 1979). Another problem confusing the taxonomy of the Pondaung primates is whether these two animals belong to the same taxonomic group or not. For example, Szalay & Delson (1979) discussed the Pondaung primates, allocating Amphipithecus to the adapiforms and Pondaungia to the early catarrhines. At that time, only a mandibular fragment preserving P3–M1 for Amphipithecus (Fig. 9.2d) had been found, while a mandibular but also a maxillary fragment preserving M1–2 had been discovered for Pondaungia (Fig. 9.2a). The upper molars of Pondaungia likely retained the ‘true hypocone’ which has been considered the definitive feature of anthropoid primates, but there was no information on the upper molars for Amphipithecus . Fig. 9.1. Geological map of central Myanmar showing primate fossil localities. Pondaung Formation: BHN, Bahin; MGN, Mogaung. Irrawaddy Sediments: YSK, Yinseik; GBN, Gwebin; CHZ, Chaingzauk (including Myokhinthar). (Modified after Geological Map of Myanmar, Myanmar …

First record of a diacodexeid artiodactyl in the middle Eocene Pondaung Formation (Myanmar)

A fragmentary maxilla referred to a new diacodexeid artiodactyl, Magwetherium burmense, n. gen. and sp., is described from Sabapondaung locality in the middle Eocene Pondaung Formation in Myanmar. Comparisons with other basal artiodactyls known in the Eocene of Asia, Europe, and North America reveal that this unexpected new taxon displays an unusual combination of derived and primitive features. Magwetherium further displays more morphological affinities with the diacodexeid Jiangsudon from the middle Eocene Shanghuang fissure fillings in eastern China than with any other Holarctic dichobunoids. This study also suggests that fossil remains from Pondaung recently described as indeterminate artiodactyls can likely be referred to dichobunids. The occurrence of a diacodexeid artiodactyl in Southeast Asia extends the fossil record of the family in this part of the continent, it represents the youngest representative of the family, and it further documents the adaptive radiation of diacodexeids in Asia during the Eocene.KurzfassungWir beschreiben hier ein fragmentarisches Oberkiefer von einer neuen diacodexeiden Paarhufer Art, Magwetherium burmense, n. gen. und n. sp., aus der Sabapondaung Lokalität in der mittel-eozänen Pondaung Formation in Myanmar. Der Vergleich mit anderen basalen Paarhufern aus dem Eozän Asiens, Europas, und Nord-Amerikas, zeigt, daß diese unerwartete, neue Art, eine ungewöhnliche Kombination primitiver und fortgeschrittener Merkmale besitzt. Darüber hinaus weist Magwetherium mehr morphologischen Ähnlichkeiten mit dem diacodexeiden Jiangsudon aus der mittel-eozänen Shanghuang Spalten-Füllung in Ost-China auf, als mit vielen anderen holarktischen Dichobunoiden. Zudem schlägt diese Studie vor, daß die fossilen Überreste aus Pondaung, die kürzlich als unbestimmte Artiodactyla beschrieben wurden, sehr wahrscheinlich den Dichobuniden zugeordnet werden können. Das Vorkommen eines diacodexeiden Paarhufers in Südostasien, erweitert den Fossilbericht dieser Familie auf diesem Kontinent. Es repräsentiert den jüngsten Vertreter dieser Familie und dokumentiert darüber hinaus die adaptive Radiation der Diacodexeiden während dem Eozän in Asien.

Erratum to: First record of a diacodexeid artiodactyl in the middle Eocene Pondaung Formation (Myanmar)

Kurzfassung Wir beschreiben hier einen fragmentarischen Oberkiefer einer neuen diacodexeiden Paarhufer-Art (Magwetherium burmense n. gen. et n. sp.) aus der Sabapondaung-Fundstelle der mittel-eozänen PondaungFormation in Myanmar. Vergleiche mit anderen basalen Paarhufern, die aus dem Eozän Asiens, Europas, und Nordamerikas bekannt sind, zeigen, dass dieses unerwartete, neue Taxon eine ungewöhnliche Kombination abgeleiteter und primitiver Merkmale besitzt. Darüber hinaus weist Magwetherium mehr morphologische Ähnlichkeiten mit der diacodexeiden Gattung Jiangsudon aus der mittel-eozänen Shanghuang-Spaltenfüllung (östliches China) auf als mit vielen anderen holarktischen Dichobunoiden. Unsere Studie legt überdies nahe, dass die kürzlich von Pondaung als unbestimmte Artiodactyla beschriebenen Fossilreste, mit großer Wahrscheinlichkeit, den Dichobunoiden zugeordnet werden können. Das Vorkommen eines diacodexeiden Paarhufers in Südostasien erweitert den Fossilbericht dieser Familie auf diesem Teil des Kontinents. Außerdem stellt es den jüngsten Vertreter dieser Familie dar und dokumentiert damit darüber hinaus die adaptive Radiation der Diacodexeiden in Asien während des Eozäns.