Stéphane Ducrocq

New Myanmar middle Eocene anthropoids. An Asian origin for catarrhines

Abstract In April 1997, several new lower jaw fragments of the primates Amphipithecus and Pondaungia were discovered in the Eocene Pondaung Formation in Central Myanmar by the Pondaung Fossil Expedition headed by the Office of Strategic Studies. These new fossils, when compared together and to Siamopithecus from the Late Eocene of Peninsular Thailand, show additional characters that testify to their anthropoid status, to their common origin and to their resemblance to some African relatives. In this paper we describe the new data displayed by these new Myanmar fossils, we identify the characters that unite these Southeast Asian primates as anthropoids and we examine the relationships of this Southeast Asian group with its African counterparts.

Mammalian faunas and the ages of the continental Tertiary fossiliferous localities from Thailand

Abstract The paleontological study of the mammalian fossils of Tertiary fossiliferous localities from Thailand, has led to the description of numerous new taxa, the modification of several extant paleobiogeographical patterns and identification of accurate dates for the Tertiary continental basins. The Krabi Basin yielded 27 distinct mammal species, most of them representing new forms, and an Upper Eocene age is now well established for this southern locality. The use of the Krabi assemblage as a reference fauna also led to the reassessment of the ages of several other Asian localities and suggests that the Thai assemblage lived in a forest under a tropical climate. All localities from northern Thailand occur in a time span ranging from 16 to 14 Ma. The use of the cenogram method, allowed the paleoenvironment of the Neogene Thai localities to be compared with contemporaneous faunal communities from the Pakistan Siwaliks and China. The middle Miocene environment in South Asia seems to have been quite open, with a likely monsoonal climate. Finally, the ages of different fossiliferous localities from Thailand are correlated with the geodynamic events following the India-Asia collision.

Eocene Krabi basin (southern Thailand): Paleontology and magnetostratigraphy

We present the magnetostratigraphy of the late Eocene Krabi section from the Krabi basin, Thailand. The investigated section is about 105 m thick and consists of red and yellow siltstones, sandstones, gray claystones, lignites, and limestones. We collected 86 samples at 43 different stratigraphic levels from the 105-m-thick section. The samples yielded a paleomagnetic direction, and paleomagnetic analyses give favorable demagnetization behaviors; two magnetic components can be isolated. Rock magnetic experiments show that the natural remanent magnetization generally results from the presence of titanomagnetite. The first component has roughly the direction of the present-day field. The second component displays only reversed polarity, with a mean direction: declination = 192.34, inclination = −15.5, N = 71, α 95 = 4.7, k = 14 (after bedding correction). Mammalian biostratigraphy indicates a late Eocene age. Correlation to the Geomagnetic Polarity Time Scale relies on biostratigraphic data previously proposed for the fauna found in the same section. These correlations have been achieved by comparing variations in the sedimentation rate derived from the alternative correlation. The proposed correlation puts the Krabi section in chron C12r or chron C13r. This suggests sedimentation rates of 4.9 and 9.4 cm/k.y., respectively. This correlation suggests that the Krabi section is older than 31 Ma and younger than 34 Ma.

Sedimentary facies of the late Middle Eocene Pondaung Formation (central Myanmar) and the palaeoenvironments of its Anthropoid Primates

Abstract The primate-bearing Pondaung Formation (northwestern part of central Myanmar) is mainly composed of cyclic sequences of sandstones and variegated clays that are divisible into 12 lithofacies and are grouped under seven facies associations. These established facies associations represent the deposition in a fluvio-deltaic environment. The anthropoid primate remains occur in swale-fill sediments, sometimes in carbonate nodules of pedogenetic origin and also, in small crevasse channel deposits of the upper part of the Pondaung Formation. The sedimentary facies associated to these anthropoid primates contribute to the understanding of their morpho-anatomic features. To cite this article: A.N.xa0Soe etxa0al., C.xa0R. Palevol 1 (2002) 153–160.

NEW REMAINS OF PONDAUNGIMYS ANOMALUROPSIS (RODENTIA, ANOMALUROIDEA) FROM THE LATEST MIDDLE EOCENE PONDAUNG FORMATION OF CENTRAL MYANMAR

Abstract Except for the few specimens previously reported from the late middle Eocene of North Africa (Algeria) and more recently from South Asia (Myanmar), the fossil record of anomaluroid rodents is relatively scarce for the Paleogene Period. In this paper, we describe new material, notably a skull, of the anomaluroid taxon Pondaungimys anomaluropsis Dawson et al., 2003, recently described from the latest middle Eocene Pondaung Formation in Central Myanmar (South Asia). Pondaungimys shows a dental pattern very similar to that of Nementchamys, an anomaluroid rodent previously reported from roughly coeval deposits in Algeria. Although Nementchamys and Pondaungimys have a dental pattern relatively more primitive in some respects than that of Miocene and modern anomalurids, in other respects they show a derived dental complexity that leads us to consider both taxa as the closest outgroups of the Anomaluridae sensu stricto (the true scaly-tailed flying squirrels) within the Anomaluroidea. Pondaungimys clearly demonstrates that the evolutionary history of the anomaluroid rodents is not limited to Africa. The widespread South Asian-North African distribution of the late middle Eocene forms strongly suggests that faunal exchanges between Africa and Asia took place during the Paleogene, a statement supported by other mammalian groups.

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.

Palaeogene anthropoid primates from Africa and Asia: new phylogenetical evidences

Abstract New discoveries of fossil primates from the Asian Palaeogene have led to reconsider the phylogenetical relationships between anthropoid primates from Asia and Africa. The data support a Tarsiidae–Anthropoidea relationship, a sister-group relationship between amphipithecids and propliopithecids, and a weak support for oligopithecid monophyly. Two biogeographical scenarios are proposed from the new phylogenies and are discussed.

EOCENE NIMRAVID CARNIVORANS FROM THAILAND

Abstract Dental remains assigned to nimravid carnivores have been discovered in southern Thailand. These specimens come from the upper Eocene Krabi Basin that has already yielded numerous vertebrate taxa important for the knowledge of mammal evolution. The fossils described here are among the oldest remains belonging to the Nimravidae, and they are attributed to Nimravus cf. intermedius and Hoplophoneus sp. The occurrence of nimravid carnivores in Southeast Asia implies exchanges between Asia and North America during the Late Eocene, and it supports a larger geographical distribution and an origin of the family older than previously known.

Discovery of new ruminant dental remains from the Middle Eocene Pondaung Formation (Myanmar): reassessment of the phylogenetic position of Indomeryx

Two new species of Indomeryx are described from the Late Middle Eocene Pondaung Formation, central Myanmar. These two species differ from I. cotteri by their more primitive dental features, thus challenging the inclusion of Indomeryx in the new Pecora family Prodremotheridae. Despite poor knowledge of this genus, we rather suggest a basal position within ruminantia, close to Archaeomeryx with which it displays several affinities.

First discovery of Helohyidae (Artiodactyla, Mammalia) in the Late Eocene of Thailand: a possible transitional form for Anthracotheriidae

Dental remains of the earliest known helohyid artiodactyl are described from the Late Eocene of Krabi in South Thailand. This new form, Progenitohyus thailandicus n.g. n.sp., is distinct from Gobiohyus, a specialized genus from the Middle Eocene of Mongolia, and it displays strong affinities with the primitive anthracotheriid Siamotherium krabiense from Krabi. Both Thai species certainly testify to an ancestor-descendant relationship, but an even earlier differentiation of Helohyidae and Anthracotheriidae should be searched for in the Middle Eocene or even earlier.