Yaowalak Chaimanee

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 Middle Miocene tarsier from Thailand and the reconstruction of its orbital morphology using a geometric–morphometric method

Tarsius is an extant genus of primates endemic to the islands of Southeast Asia that is characterized by enormously enlarged orbits reflecting its nocturnal activity pattern. Tarsiers play a pivotal role in reconstructing primate phylogeny, because they appear to comprise, along with Anthropoidea, one of only two extant haplorhine clades. Their fossils are extremely rare. Here, we describe a new species of Tarsius from the Middle Miocene of Thailand. We reconstructed aspects of its orbital morphology using a geometric–morphometric method. The result shows that the new species of Tarsius had a very large orbit (falling within the range of variation of modern Tarsius) with a high degree of frontation and a low degree of convergence. Its relatively divergent lower premolar roots suggest a longer mesial tooth row and therefore a longer muzzle than in extant species. The new species documents a previous unknown Miocene group of Tarsius, indicating greater taxonomic diversity and morphological complexity during tarsier evolution. The current restriction of tarsiers to offshore islands in Southeast Asia appears to be a relatively recent phenomenon.