First discovery of colobine fossils from the Late Miocene/Early Pliocene in central Myanmar.

Here we report two kinds of colobine fossils discovered from the latest Miocene/Early Pliocene Irrawaddy sediments of the Chaingzauk area, central Myanmar. A left mandibular corpus fragment preserving M1-3 is named as a new genus and species, Myanmarcolobus yawensis. Isolated upper (M(1)?) and lower (M2) molars are tentatively identified as Colobinae gen. et sp. indet. Although both forms are medium-sized colobines, they are quite different from each other in M2 morphology. The isolated teeth of the latter show typical colobine-type features, so it is difficult to identify their taxonomic position, whereas lower molars of Myanmarcolobus have unique features, such as a trapezoid-shaped long median lingual notch, a deeply concave median buccal cleft, a strongly developed mesiobuccal notch, and rather obliquely running transverse lophids. Compared with fossil and living Eurasian colobine genera, Myanmarcolobus is most similar in lower molar morphology to the Pliocene Dolichopithecus of Europe rather than to any Asian forms. In Dolichopithecus, however, the tooth size is much larger and the median lingual notch is mesiodistally much shorter than that of Myanmarcolobus. The discovery of Myanmarcolobus in central Myanmar is the oldest fossil record in Southeast Asia not only of colobine but also of cercopithecid monkeys and raises many questions regarding the evolutionary history of Asian colobine monkeys.

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 P(4)-M(3) and mandibular fragments with C-P(3) and M(2-3). This study reports new materials for the genus, including a humeral head fragment, a lingual fragment of the right M(2), a lingual fragment of the right M(3), and a left I(1). 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 I(1) 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 I(1) does not support the notharctine hypothesis of the Amphipithecidae.

The extinct river shark Glyphis pagoda from the Miocene of Myanmar and a review of the fossil record of the genus Glyphis (Carcharhiniformes: Carcharhinidae).

We redescribe an extinct river shark, Glyphis pagoda (Noetling), on the basis of 20 teeth newly collected from three different Miocene localities in Myanmar. One locality is a nearshore marine deposit (Obogon Formation) whereas the other two localities represent terrestrial freshwater deposits (Irrawaddy sediments), suggesting that G. pagoda from the Irrawaddy sediments was capable of tolerating low salinity like the extant Glyphis. Glyphis pagoda likely reached up to at least 185 cm in total body length and was probably piscivorous. The fossil species occurs in rocks of Myanmar and eastern and western India and stratigraphically ranges at least from the Lower Miocene (Aquitanian) to the lower Upper Miocene (mid-Tortonian). It has been classified under at least eight other genera to date, along with numerous taxonomic synonyms largely stemming from the lack of understanding of the heterodonty in extant Glyphis in the original description. Our literature review suggests that known Miocene shark faunas, particularly those in India, are manifested with unreliable taxonomic identifications and outdated classifications that warrant the need for a comprehensive taxonomic review in order to evaluate the evolutionary history and diversity pattern of Miocene shark faunas. The genus Glyphis has a roughly 23-million-year-long history, and its success may be related to the evolution of its low salinity tolerance. While extant Glyphis spp. are considered to be particularly vulnerable to habitat degradation and overfishing, the fossil record of G. pagoda provides renewed perspective on the natural history of the genus that can be taken into further consideration for conservation biology of the extant forms.

[Jaws of primitive mammals].

Some of main osteological differences between mammals and reptiles are seen in the number of bones that constitute lower jaw and in jaw articulation. A lower jaw of mammals consists of only one bone, while in reptiles it consists of several bones (e.g., four to six in lizards and five in crocodiles). The jaw articulation in mammals is performed by squamosal of the skull and the mandible ( = dentary), while in reptiles it is done by quadrate of the skull and articular of the lower jaw. When mammals first appeared about 200 million years ago in the Mesozoic Era, the jaws of primitive mammals were morphologically intermediate between those of reptiles and typical mammals. Here, I briefly introduce the evolution of lower jaw morphology from the reptilian one to the mammalian one, showing lower jaw features of some mammal-like reptiles and primitive mammals.

Endocranial cast and morphology of the olfactory bulb of Amphipithecus mogaungensis (latest middle Eocene of Myanmar).

A detailed endocranial cast of the olfactory bulb of Amphipithecus mogaungensis, a latest middle Eocene primate from the Pondaung Formation (Myanmar), was studied in comparison with some Paleogene primates, the olfactory bulb of which has been reported. The olfactory bulb of Amphipithecus is located just anterior to the postorbital constriction, that is, within the interorbital septum. It is relatively large and pedunculate, not overlapped by the frontal lobe, and consists of two parallel aligned bodies. The relative volume of the olfactory bulb shows the same pattern as in adapiforms, but the location and bilobed form are more similar to those of omomyoids than of adapiforms.

Variation in maxillary sinus anatomy among platyrrhine monkeys.

Variations in the maxillary sinus anatomy of extant and fossil catarrhine primates have been extensively examined using computed tomography (CT), and have potential utility for phylogenetic analyses. This approach has also been used to demonstrate its anatomical variation in eight of the 16 extant genera of platyrrhines and the absence of the sinus in Saimiri and Cacajao. We used this approach to evaluate the three-dimensional anatomy of the maxillary sinus in all extant platyrrhine genera, and here argue the phylogenic implications of this variation. This study confirms, for the most part, previous CT studies and augments them with the six genera not studied previously: Ateles, Lagothrix, Callithrix, Cebuella, Pithecia and Chiropotes. The entire maxilla is pneumatized by the sinus in the atelines, Cebus, and Callicebus, whereas the sinus pneumatizes only the medial part of the maxilla in the callitrichines and Aotus. Pithecia has a unique conformation in which the maxillary sinus and the expanded inferior meatus pneumatize the posteromedial and anterolateral parts of the entire maxilla, respectively. Chiropotes has no sinus, and the inferior meatus possibly expands into the area between the middle meatus and medial surface of the maxilla to disturb sinus formation, as in the case of its close relative Cacajao. Finally, we argue that the sinus that pneumatizes the entire maxilla is a primitive feature in extant platyrrhines and was probably shared by the last common ancestor of the anthropoids.

Mammalian dispersal at the Paleocene/Eocene boundary.

A profound faunal reorganization occurred near the Paleocene/Eocene boundary, when several groups of mammals abruptly appeared on the Holarctic continents. To test the hypothesis that this event featured the dispersal of groups from Asia to North America and Europe, we used isotope stratigraphy, magnetostratigraphy, and quantitative biochronology to constrain the relative age of important Asian faunas. The extinct family Hyaenodontidae appeared in Asia before it did so in North America, and the modern orders Primates, Artiodactyla, and Perissodactyla first appeared in Asia at or before the Paleocene/Eocene boundary. These results are consistent with Asia being a center for early mammalian origination.