The Namdapha flying squirrel (Biswamoyopterus biswasi) is a rare species of flying squirrel native to India. It was the sole member in the genus Biswamoyopterus until the description of the Laotian giant flying squirrel (Biswamoyopterus laoensis) in 2013. In 2018, Quan Li from the Kunming Institute of Zoology at the Chinese Academy of Sciences discovered a new squirrel in the same genus while studying specimens in their collection called the Mount Gaoligong flying squirrel (Biswamoyopterus gaoligongensis), based on the region it was discovered in.
The Namdapha flying squirrel has reddish, grizzled fur with white above. Its crown is pale grey, its patagium is orangish and its underparts are white. Flying squirrels are not capable of flight like birds or bats; instead, they glide between trees. The direction and speed of the animal in midair are varied by changing the positions of its limbs, largely controlled by small cartilaginous wrist bones. There is a cartilage projection from the wrist that the squirrel holds upwards during a glide. This specialized cartilage is only present in flying squirrels and not other gliding mammals. This cartilage along with the manus forms a wing tip to be used during gliding. After being extended, the wing tip may adjust to various angles, controlling aerodynamic movements. The wrist also changes the tautness of the patagium, a furry parachute-like membrane that stretches from wrist to ankle. The tail acts as an adjunct airfoil, working as an air brake before landing on a tree trunk.
Namdapha flying squirrels are native to Arunachal Pradesh in northeast India, where a single specimen was collected in Namdapha National Park in 1981. They inhabit tall Mesua ferrea jungles, often on hill slopes in the catchment area of the Dihing River (particularly on the western slope of the Patkai range) in northeastern India.
Namdapha flying squirrels are very elusive; due to this, all of them have been described relatively recently. They live in trees and are active during the nighttime hours. They prefer to spend time singly but during cold months they may share one nest in order to keep warm.
Namdapha flying squirrels are herbivores (frugivores, granivores). They eat various fruits, nuts, seeds, fungi, flowers, and tree sap.
Little information is available about the reproductive habits of Namdapha flying squirrels. Females are known to give birth to up to 6 young per litter. The young are born in a nest and are at first naked and helpless.
The range of the Namdapha flying squirrel may be restricted to a single valley and it is threatened by poaching of animals for food from within the park, and possibly by habitat destruction. It is among the 25 "most wanted lost" species that are the focus of Global Wildlife Conservation's "Search for Lost Species" initiative.
The IUCN Red List and other sources don’t provide the number of the Namdapha flying squirrel total population size. Currently, this species is classified as Critically Endangered (CR) on the IUCN Red List, and its numbers today are decreasing.