Jean-Jacques Jaeger

A Middle Miocene hominoid from Thailand and orangutan origins

The origin of orangutans has long been debated. Sivapithecus is considered to be the closest ancestor of orangutans because of its facial–palatal similarities, but its dental characteristics and postcranial skeleton do not confirm this phylogenetic position. Here we report a new Middle Miocene hominoid, cf. Lufengpithecus chiangmuanensis n. sp. from northern Thailand. Its dental morphology relates it to the Pongo clade, which includes Lufengpithecus, Sivapithecus, Gigantopithecus, Ankarapithecus and possibly Griphopithecus. Our new species displays striking dental resemblances with living orangutans and appears as a more likely candidate to represent an ancestor of this ape. In addition, it originates from the geographic area of Pleistocene orangutans. But surprisingly, the associated flora shows strong African affinities, demonstrating the existence of a temporary floral and faunal dispersal corridor between southeast Asia and Africa during the Middle Miocene, which may have played a critical role in hominoid dispersion.

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.

Ages and paleoenvironment of Miocene mammalian faunas from Thailand

Abstract The geological survey of continental basins in northern Thailand has led to the discovery and the study of several mammalian assemblages in that area. All localities from northern Thailand occur in a time span ranging from about 16 to 14 Ma. In addition, a diachronism is apparent among the different localities and is indicated by the different stages of evolution in the tooth morphology of rodents, ruminants, rhinos and mastodonts. Mae Long (Li Basin) would be the oldest locality (about 16 Ma), followed by Had Pu Dai (Lampang Basin), and then Huai Siew and Ban San Klang (both in Pong Basin). Ban Na Sai (Li Basin) and Mae Teep would be contemporaneous with Ban San Klang, and Mae Moh is thought to be the youngest locality. In order to study the paleoenvironment of the Thai Neogene faunas, we have used the cenogram method in which structure reflects the general environment of a faunal community. We also compared the faunal communities from Thailand with those from the Pakistan Siwaliks and from China. In the latter areas, the microfauna is well represented and the large mammals are numerous, thus suggesting a wet environment with a likely monsoonal climate. The Middle Miocene paleoenvironment in South Asia seems to have been quite open, and small areas of forests were probably intermixed with grassland. The cenogram structure completely excludes an environment dominated by primary forest or by steppe.

New Phiomorpha and Anomaluridae from the Late Eocene of North-West Africa: Phylogenetic Implications

Until recently, the ancient fossil family Phiomyidae (suborder Hystricognathi) was recorded only from the early Oligocene site of the Fayum, Egypt (Andrews, 1906; Osborn, 1908; Schlosser, 1910, 1911; Wood, 1968). As defined by Lavocat (1973), the infraorder Phiomorpha includes many other representatives that occurred in the middle or late Oligocene of the Balearic islands (Adrover and Hugueney, 1975; Adrover et al., 1978), in the Miocene of Africa (Stromer, 1926; Lavocat, 1973), of India and Pakistan (Black, 1972; Flynn and Jacobs, 1982; Flynn et al., 1983; Jaeger et al., 1980), and of the eastern Mediterranean (Chios, Greece) (Tobien, 1968). Phiomorphs are still represented in Africa by two living families: the Thryonomyidae and Petromyidae (or Petromuridae). At the Fayum site, Wood (1968) described five new genera and nine species of phiomyids, showing a great variety of dental patterns (three to six crests in upper and lower molars, for example), but possessing already in the Oligocene all the characteristics of the modern representatives of the thryonomyoids: retention of dP4/4; hystricomorphy; hystricognathy; and multiserial enamel on the incisors.

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.

A new genus of Macroscelidea (Mammalia) from the Eocene of Algeria: a possible origin for elephant-shrews

Abstract Nementchatherium senarhense, gen. et sp. nov. from the Middle–Late Eocene of Bir El Ater (Algeria) is described and assigned to the subfamily Herodotiinae (Macroscelidea). This genus and the other primitive elephant-shrews are compared with the Louisininae (Hyopsodontidae, Condylarthra) from the Early Paleogene of Europe. These groups have been included in a phylogenetic analysis based on dental characters, in order to clarify the origin of Macroscelidea. Phylogenetic reconstruction suggests that Louisininae are belonging in the polyphyletic Hyopsodontidae except for Microhyus which is considered here as the sister-group the Macroscelidea. These results suggest a terrestrial interchange between Africa and Eurasia during the Early Eocene. The phylogenetic analysis suggests also that the Macroscelidea-Microhyus clade is closely related to the Proboscidea. Like molecular phylogenies, especially those concerning the African molecular clade (=Afrotheria), our results, provide evidence for a macroscelid-tethytherian relationship. However, if the Macroscelidea emerged from European “condylarth” at the Early Eocene as our data suggest, the Proboscidea are already differentiated in Africa during this period. Then, it seems that Macroscelidea and Proboscidea are paraphyletic. The assumption of a unique group of condylarthran type at the origin of Afrotheria (macroscelids, tethytherians, tubulidentates, tenrecid and chrysochlorid insectivores) cannot be excluded, but the current paleontological data do not fit with that hypothesis.

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.

Magnetostratigraphy of the Middle Miocene continental sedimentary sequences of the Mae Moh Basin in northern Thailand: evidence for counterclockwise block rotation

Abstract A magnetostratigraphic study has been performed on the Mae Moh basin, well known for its lignite mining in the Lampang province. Paleomagnetic samples were collected from 66 stratigraphic levels. Rock magnetic investigations indicate the presence of low coercivity minerals. Specimens subjected to progressive thermal (or alternating field) demagnetization procedures show that nearly all of them exhibit a low temperature magnetization component, and a high temperature characteristic component (ChRM), with either positive or negative virtual geomagnetic pole latitudes and opposite polarity, considered as the characteristic Miocene magnetization. The overall mean paleomagnetic direction (incl.=22.2°, decl.=358.3°, κ =15, α 95 =4) documents a counterclockwise vertical axis rotation of about 13°±1.32 with respect to the expected Miocene direction derived from the Eurasian polar wander curve (incl.=42°, decl.=11°). Our paleomagnetic results are not consistent with the previously reported paleomagnetic data. The rotation observed in the Mae Moh basin can be the response to local tectonics. A section sampled for magnetostratigraphy reveals a polarity sequence of nine magnetozones that can reliably be correlated to the geomagnetic polarity time scale. According to biochronological constraints, the magnetostratigraphic results from the mammal-bearing succession correlate with chron C5ABn–C5An2n, between 13.5 and 12.1 Ma. According to the mean sedimentation rate of about 17.5 cm/ka, ages of 12.5 and 12.8 Ma are proposed for the fossiliferous levels (J5 and K1, K2 lignite zones) were the mammal remains were found.

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 lower jaw of Siamopithecus eocaenus from the Late Eocene of Thailand.

We describe here a nearly complete lower jaw of Siamopithecus eocaenus from the Late Eocene of Peninsular Thailand. It displays several new characters, such as the symphysis, the horizontal branch, part of the vertical branch and most of its anterior dentition. The symphysis is nearly vertical and bears most characteristics of that of derived anthropoids but is unfused. Incisors were not preserved. A large canine, P/2 alveolus and P/3-M/3 were preserved. P/2 is rooted and reduced. The morphology of P/3 and P/4 is characteristic of that of anthropoids, with an oblique position in the tooth row, a labially displaced anterior root of P/3 and P/4 and the presence of a lingually developed metaconid on P/4. The premolars display a primitive stage of anthropoid evolution. This discovery confirms the anthropoid status of Siamopithecus, its attribution to the family Amphipithecidae and demonstrates the importance of Asia in the evolution of anthropoid primates.