Eocene Pondaung Formation Research Articles

Neochorlakkia myaingensis n. gen., n. sp., a new Dichobunidae (Mammalia, Cetartiodactyla) from the middle Eocene Pondaung Formation, Myanmar

The diversity of basal ungulates is significant in the late middle Eocene Pondaung Formation (Myanmar). However, the precise identification or attribution of some fossils is sometimes difficult because of the scarcity and poor preservation of the material. We describe here a new genus and species of a Dichobunidae from Paukkaung Kyitchaung 2 locality, that is morphologically and probably phylo­genetically close to a taxon from the early-middle Eocene of Pakistan, and we discuss the attribution of dental material to Myanmarius chitseini Tsubamoto, Egi, Takai, Htike & Zin-Maung-Maung-Thein, 2013, an inderterminate artiodactyl from Pondaung. This study also confirms that dispersals were possible between the Indian subcontinent and Southeast Asia during the first part of the Eocene.

First report of the lower dentition of Siamotherium pondaungensis (Cetartiodactyla, Hippopotamoidea) from the late middle Eocene Pondaung Formation, Myanmar

First report of the lower dentition of Siamotherium pondaungensis (Cetartiodactyla, Hippopotamoidea) from the late middle Eocene Pondaung Formation, Myanmar

New basal ruminants from the Eocene of the Pondaung Formation, Myanmar

ABSTRACT Two new genera and species of small basal ruminants are described from the middle Eocene Pondaung Formation in Myanmar. One form, Paukkaungmeryx minutus, gen. et sp. nov., is attributed to a primitive Archaeomerycidae, and the other, Stenomeryx bahinensis, gen. et sp. nov., very likely represents the oldest known Tragulidae, a family unknown in Pondaung so far. The fossil record of primitive ruminants in Pondaung is now represented by five genera, and the occurrence of both of these taxa in the Paleogene of Myanmar supports the hypothesis that the initial radiation and diversification of basal ruminants probably occurred during the first part of the Eocene in southern Asia. These discoveries also demonstrate that the fossiliferous sediments of the Pondaung Formation continue to yield new vertebrate taxa that help documenting the evolutionary history of several groups of small mammals.

Astragalus of Pondaungimys (Rodentia, Anomaluroidea) from the late middle Eocene Pondaung Formation, central Myanmar

ABSTRACTA well-preserved astragalus of the anomaluroid rodent Pondaungimys anomaluropsis is described from the late middle Eocene Pondaung Formation of central Myanmar. This specimen is the first postcranial element of a rodent from the Pondaung Formation and the oldest postcranial fossil currently known for Anomaluroidea. It illuminates plesiomorphous postcranial conditions in early anomaluroids and provides a basis for reconstructing the evolution of arboreal locomotion in this group of rodents. In contrast to those of living anomaluroids, the astragalus of Pondaungimys bears features indicating a less mobile ankle, specifically including a reduced range of plantarflexion at the upper ankle joint and a diminished capacity for inversion at the lower ankle joint. Its anatomy suggests that early anomaluroids were generalized quadrupeds, with intermediate arboreal adaptations between those of paramyids and modern anomaluroids. A cladistic analysis based on astragalar characters corroborates a basal position for Pondaungimys among anomaluroids. The phylogenetic signal derived from astragalar morphology is consistent with recent assessments of relationships among living anomaluroids based on craniodental characters and molecular data. Stem anomaluroids such as Pondaungimys apparently lacked the ability to glide, a locomotor pattern that is retained in extant Zenkerella.

New hyaenodonta (Mammalia) from the middle Eocene of Myanmar

The middle Eocene Pondaung Formation in Myanmar has yielded a rich mammalian fauna including several Primate taxa. Hyaenodonta are known by the genera Kyawdawia, Yarshea, Orienspterodon, and two other indeterminate taxa. We describe here new material of Kyawdawia, including some morphological details, a new species of the hypercarnivorous genus Propterodon and an indeterminate species, different from those described earlier in Myanmar, and characterized by a reduction of m3 and would belong to a third lineage with the same evolutionary trend as Galecyon and the Limnocyoninae. The hyainailourines (Orienspterodon) and hyaenodontines (Propterodon) are recorded for the first time in Southeast Asia and these subfamilies appeared in quasi the same time in Europe illustrating probably a profound change in the carnivorous fauna among Laurasia.

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 …

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

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

Body mass estimation from the talus in primates and its application to the Pondaung fossil amphipithecid primates

The relationship between talar size and body mass in extant primates is examined to provide the regression equations for estimating the body mass of extinct primate species based on the talar size. The results indicate that, among the linear talar dimensions, the whole talar size and the tibial trochlear size are good body mass estimators for primates. As an example, the regression equations presented here were applied to the body mass estimates of the fossil tali (NMMP-39 and NMMP-82) of the amphipithecid primates from the middle Eocene Pondaung Formation of Myanmar. Based on the estimated body masses determined by this study, NMMP-39 (estimated body mass: ca. 2.7 kg) should likely be assigned to Ganlea megacanina or Myanmarpithecus yarshensis, while NMMP-82 (estimated body mass: ca. 4.9 kg) should likely be assigned to ‘Amphipithecus’ mogaungensis or Pondaungia cotteri.

Late middle Eocene fossil wood of Myanmar: Implications for the landscape and the climate of the Eocene Bengal Bay

The late middle Eocene Pondaung Formation, Myanmar, has yielded a diversified assemblage of silicified wood including some of the earliest recorded Dipterocarpaceae. However, mid-Palaeogene fossil wood from Asia remains rarely described. We present here three additional species of fossil wood from the upper member of the Pondaung Formation, including a new species of Menispermoxylon (M. mowglii nov. spec.) with successive cambia and included phloem, and two specimens of the fossil genera Glutoxylon (G. burmense Chowdhury) and Heritieroxylon (H. arunachalensis Lakhanpal, Prakash et Awasthi). These three fossil species are related to modern taxa of mangrove and coastal forests in the Bengal Bay and complete the floral assemblage already identified in the Pondaung Formation. The late middle Eocene fossil woods of Myanmar followed a toposequence with mangroves along the seashore, riparian elements similar to those of modern Terai ecosystem in the upper delta plain, and dry dipterocarp forests in the upstream areas of the drainage basin. The latter two assemblages and their association in the landscape are typical of monsoonal areas with significant rainfall and a marked dry season, thus confirming recent studies showing that the Bengal Bay has experienced a significant monsoonal regime as early as 40Ma ago. The climatic parameters obtained by two quantitative botanical approaches on the Pondaung fossil wood, the coexistence and wood anatomical approaches, suggest similar-to-modern rainfall amount, marked dry season, and warmer annual temperature for the Eocene of Myanmar. They thus support the hypothesis that monsoonal rainfall at that time may have been favored by Eocene greenhouse conditions. However, despite the homogeneity of the Pondaung floral assemblage, several resulting climatic parameters, such as the mean annual temperature (for the coexistence approach) or the mean annual rainfall (for the wood anatomical approach), display large but incomplete uncertainty intervals or unlikely values (for the coexistence and wood anatomical approaches respectively). These limitations can be attributed to the lack of super-warm and super-seasonal stations in their modern databases. It thus indicates that results from both quantitative approaches should be interpreted with caution for palaeo-monsoon reconstruction.

Fossil woods from the late middle Eocene Pondaung Formation, Myanmar

Twelve species of fossil wood were identified from silicified specimens collected in the late middle Eocene Pondaung Formation, Myanmar. These species display affinities with modern Fabaceae, Moraceae, Combretaceae, Sapindaceae, Malvaceae, Dipterocarpaceae and Theaceae. They include five new species of the fossil genera Ficoxylon (F. mogaungense sp. nov.), Sapindoxylon (S. burmense sp. nov.), Bombacoxylon (B. pondaungense sp. nov.), Shoreoxylon (S. panganense sp. nov.) and Schimoxylon (S. benderi sp. nov.). This material represents the oldest record of fossil dipterocarps so far reported outside the Indian subcontinent. It reflects different ecotones of a dry dipterocarp forest, with coastal, riparian, and inland elements. The Burmese fossil assemblage further contrasts with the common idea that lowland rainforests were widespread in Southeast Asia during the Eocene. It suggests that the climate in the proto-Bengal Bay was more seasonal than previously thought. This confirms that early Dipterocarpaceae were adapted to seasonally dry climates, despite the modern prevalence of warm humid tropical species.

A New Genus and Species of Bunodont Artiodactyl from the Eocene Pondaung Formation, Myanmar

Abstract A new genus and species of small bunodont artiodactyl (Mammalia), Myanmarius chitseini, is established on the basis of molar specimens from the upper middle Eocene Pondaung Formation, Myanmar. The specimens consist of upper molars and one m3. The m3 is provisionally referred to this species. Myanmarius is characterized by a low crown, bunodont cusps, a wide crushing trigon basin, a large metaconule, a reduced paraconule, a protocone distinctly larger than the other main cusps, an obtuse angled and inverted V-shaped centrocrista, a mesiodistally oriented postprotocrista and premetacristule, a buccally shifted and almost mesiodistally oriented cristid obliqua, no hypocone, no styles, and no lingual separation into two (mesial and distal) lobes of the upper molars. Our cladistic analysis supports the raoellid affinity of Myanmarius, which is nested with Khirtharia. However, if the m3 is excluded from the hypodigm of Myanmarius, the cladistic analysis rather supports the suoid affinity of Myanmarius....

Role of permeability barriers in alluvial hydromorphic palaeosols: The Eocene Pondaung Formation, Myanmar

AbstractThis study examines the lateral distribution of hydromorphy in the fine‐grained alluvial deposits of the Eocene Pondaung Formation, central Myanmar. Through detailed outcrop analysis and using a combined sedimentological and pedological approach, this study proposes a reconstruction of Pondaung overbank floodplain palaeoenvironments. The variations of hydromorphic features in the different overbank sub‐environments are then discussed and used to build a model of hydromorphic variability in alluvial deposits. Two main architectural associations with distinctive lithofacies and pedogenic features were identified, corresponding to different sub‐environments: heterolithic deposits and extensive mudstone successions. The heterolithic deposits display variegated fine‐grained lithofacies and contain poorly developed palaeosols with gley and vertic features, which are interpreted to reflect a seasonal wetlands landscape, developed in actively aggrading avulsion belts. Extensive mudstone successions with Vertisols that locally exhibit mukkara‐style pseudogley features are interpreted to represent a distal open‐forested environment. The palaeosols of both sub‐environments display dense local hydromorphic variations they are also characterized by a gradual shift from gley‐dominated to pseudogley‐dominated features with increasing distance from the avulsion belt. The clay‐dominated lithology of the floodplain parent material, which forms numerous subsurface permeability barriers, is shown to have acted as a fundamental control in limiting water‐table dynamics in coarse‐grained parts of the succession, thereby favouring hydromorphic variability. Palaeosol sequences of the Pondaung Formation contrast with the soil‐landscape associations described in other studies and provide an alternative model with which to account for the hydromorphic variability in poorly drained, alluvial soils. The model proposed as an outcome of this study demonstrates that hydromorphic variations can be dramatic in floodplains where permeability barriers are numerous. Further, the model stresses the importance of undertaking detailed lateral palaeosol analyses prior to making interpretations regarding hydromorphic variability.

Giant lizards occupied herbivorous mammalian ecospace during the Paleogene greenhouse in Southeast Asia

Mammals dominate modern terrestrial herbivore ecosystems, whereas extant herbivorous reptiles are limited in diversity and body size. The evolution of reptile herbivory and its relationship to mammalian diversification is poorly understood with respect to climate and the roles of predation pressure and competition for food resources. Here, we describe a giant fossil acrodontan lizard recovered with a diverse mammal assemblage from the late middle Eocene Pondaung Formation of Myanmar, which provides a historical test of factors controlling body size in herbivorous squamates. We infer a predominately herbivorous feeding ecology for the new acrodontan based on dental anatomy, phylogenetic relationships and body size. Ranking body masses for Pondaung Formation vertebrates indicates that the lizard occupied a size niche among the larger herbivores and was larger than most carnivorous mammals. Paleotemperature estimates of Pondaung Formation environments based on the body size of the new lizard are approximately 2–5°C higher than modern. These results indicate that competitive exclusion and predation by mammals did not restrict body size evolution in these herbivorous squamates, and elevated temperatures relative to modern climates during the Paleogene greenhouse may have resulted in the evolution of gigantism through elevated poikilothermic metabolic rates and in response to increases in floral productivity.

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.

The oldest anthropoid primates in SE Asia: Evidence from LA-ICP-MS U–Pb zircon age in the Late Middle Eocene Pondaung Formation, Myanmar

The Late Middle Eocene Pondaung Formation, central Myanmar hosts the richest deposit of terrestrial mammals in SE Asia. The Pondaung Formation contains anthropoid primates, such as Eosimiidae, Amphipithecidae and the new Afrotarsiidae, plus adapiform primates and is a critical locality in discussions on anthropoid origins and biogeography. The sands of the Pondaung Formation were derived from the erosional unroofing of a dissected andesitic volcanic arc and deposited on the forested floodplains of a large tropical river. Previously, the age of the Pondaung Formation was estimated to be Middle to Late Eocene based on stratigraphic evidence, Late Middle Eocene (Bartonian) based on comparisons with mammals from North America and Europe, 37.2±1.3Ma and 38.8±1.4Ma based on fission track dating and 37.4–37.0Ma based on questionable magnetostratigraphic correlations. Here, we report a new LA-ICP-MS, U–Pb age for zircons from a tuffaceous bed in the Pondaung Formation of 40.31±0.65Ma and 40.22±0.86Ma which is slightly older than the debatable magnetostratigraphic ages of 37–36Ma and 38–39Ma for the anthropoids from Egypt and Libya. Pending the acquisition of similarly reliable radiometric dates from all the North African and Asian sites, this new date provides support for an Asian origin for the anthropoids. Our new dates are close to the molecular clock date for the origin of the anthropoid primates and may provide a reliable calibration point for the molecular phylogenetic method.

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.

The phylogenetic affinities of the Pondaung tali

The phylogenetic affinities of the primates of the late middle Eocene Pondaung Formation of Myanmar have long been disputed. The discovery of the NMMP 39 talus (Marivaux et al.: Proc Natl Acad Sci USA 100 (2003) 13173-13178) provided the first clear evidence from the postcranium that a relatively large-bodied haplorhine primate is represented in the Pondaung fauna. Another talus (NMMP 82; Marivaux et al., 2010). Talar morphology, phylogenetic affinities and locomotor adaptation of a large-bodied amphipithecid primate from the late middle Eocene of Myanmar, Am J Phys Anthropol DOI: 10.1002/ajpa.21307) has been recently recovered which also pertains to Haplorhini. The metric and nonmetric features supporting the hypothesis of anthropoid affinities for NMMP 39 have been criticized by Gunnell and Ciochon (Gunnell GF, Ciochon RL. 2008. Revisiting primate postcrania from the Pondaung Formation of Myanmar. In: Fleagle JG, Gilbert CC, editors. Elwyn Simons: a search for origins. New York: Springer. p 211-228). Their analysis, however, was based on a very limited choice of variables, taxa, and individuals. Based on an extended sample, we are able to produce both principal components and discriminant functions that yield a rather clear separation of extant haplorhine and strepsirhine tali. Both principal components and discriminant function scores of the Pondaung tali fall with those of haplorhine primates. In addition, the Pondaung tali lack all the derived nonmetric features characteristic of strepsirhine primates, but exhibit all the features characteristic of haplorhine primates. We dispute the features Gunnell and Ciochon (2008) claim are uniquely shared by the Pondaung tali and adapiforms. Their rejection of the phylogenetic significance of the features shared by these tali and haplorhines is unwarranted by the evidence. Based on both metric and nonmetric features, the Pondaung tali are structurally most similar to the tali of haplorhines, particularly anthropoids.

A new primate from the Eocene Pondaung Formation of Myanmar and the monophyly of Burmese amphipithecids

The family Amphipithecidae is one of the two fossil primate taxa from Asia that appear to be early members of the anthropoid clade. Ganlea megacanina, gen. et sp. nov., is a new amphipithecid from the late middle Eocene Pondaung Formation of central Myanmar. The holotype of Ganlea is distinctive in having a relatively enormous lower canine showing heavy apical wear, indicating an important functional role of the lower canine in food preparation and ingestion. A phylogenetic analysis of amphipithecid relationships suggests that Ganlea is the sister taxon of Myanmarpithecus, a relatively small-bodied taxon that has often, but not always, been included in Amphipithecidae. Pondaungia is the sister taxon of the Ganlea + Myanmarpithecus clade. All three Pondaung amphipithecid genera are monophyletic with respect to Siamopithecus, which is the most basal amphipithecid currently known. The inclusion of Myanmarpithecus in Amphipithecidae diminishes the likelihood that amphipithecids are specially related to adapiform primates. Extremely heavy apical wear has been documented on the lower canines of all three genera of Burmese amphipithecids. This distinctive wear pattern suggests that Burmese amphipithecids were an endemic radiation of hard object feeders that may have been ecological analogues of living New World pitheciin monkeys.