Scaly-tailed Flying Squirrels: The fossil record

So far only one species of fossil scaly-tailed flying squirrel has been discovered with modern day ancestors of the genus Anomalurus. In addition there is an extinct genus called Paranomalurus that has three described species from Kenya and Uganda in Africa. It appears that the scaly-tailed flying squirrels have arisen from an extinct group known as the Family Zegdoumyidae, which is thought to be a sister group of the squirrels of the Family Sciuridae and the European dormice of the Family Gliridae. Several related extinct genera known as Nementchamys and Pondaugimys share characters with some fossil and living scaly-tailed flying squirrels, especially of the genus Anomalurus. However these cannot be formally included within the Anomaluridae because of their peculiar dentition and the current lack of diagnostic postcranial remains to confirm whether they were able to glide. Nonetheless these genera are thought to be the closest relatives of the Family Anomaluridae within the Superfamily Anomaluroidea, and are placed in their own family called the Nementchamyidae.

The discovery of the fossil species named Pondaugimys anomaluropsis in Burma provides evidence for the presence of anomaluroid rodents outside Africa since at least the middle Eocene some 40 million years ago. The close relationship of the genera Pondaugimys and Nementchamys emphasises the previously widespread south Asian—north African distribution of the anomaluroid rodents, thus suggesting faunal exchange between southern Asia and Africa during the Paleogene (between 65 and 23 mya). This is also supported by discoveries in the late Eocene of Thailand in the Krabi Basin and the early Oligocene of Pakistan (Bugti Hills) that confirm the occurrence of anomaluroid rodents in southern Asia. It has been proposed that they probably became extinct in southern Asia at the end of the Oligocene as a consequence of major environment changes in this area resulting from significant paleogeographic and geomorphologic events.

The retreat of the Paratethys Sea, a large shallow sea that stretched from the region north of the Alps over Central Europe to the Aral Sea in western Asia, which occurred at the end of the Paleogene during the formation of the Himalayan highlands, played an important role in reforming atmospheric circulation leading to climatic deterioration. Although tropical conditions in southern Asia were maintained at least during some of the Oligocene, tectonic events at the end of the Paleogene and during the Miocene seem to have involved drastic climatic changes; as testified by some late Oligocene mammal communities from Pakistan, suggesting locally drier and more open environments. In contrast, more stable climatic conditions in Africa during the Neogene (24–1.8 mya) favoured the adaptive radiation of anomalurid rodents. Anomaluroid rodents are thought to be deeply rooted in the early Paleogene radiation of the Zegdoumyidae in Africa. However, the Zegdoumyidae are too poorly represented to strongly claim an African origin for anomaluroid rodents. In the absence of a comprehensive early Paleogene fossil record both in Africa and in South Asia, the question of their higher phylogenetic and paleobiogeographic origins remains still open.