Intro: Origins and evolution

In order to better understand the different species of gliding mammals that exist today and where they have come from, we need to look at the hidden treasures of the fossil record. This will help us to understand how the present-day gliding mammals evolved and where they previously occurred.

The age of the fossil record of the different groups of gliding mammals varies enormously, ranging from as far back as the early Eocene (50 mya) for the scalytailed flying squirrels to the late Eocene (40 mya) for the flying squirrels. The fossil record of the enigmatic colugos also appears to extend as far back as the Eocene (50 mya). The gliding marsupials have more recent origins with the fossil record dating back to the late Oligocene to Early Miocene (approximately 24–18 mya).

In addition to the groups of gliding mammals we know today, there are at least three extinct species of gliding mammals from different families that have no surviving relatives. The first extinct glider is from the Family Gliridae. This species, Glirulus lissiensis (meaning ‘little dormouse from Lissieu’), was first collected from the upper Miocene (c. 10 mya) deposits in Lissieu, France, and was initially described in 1965 as a non-gliding rodent.

However, subsequent discoveries of similar fossils from the upper Miocene deposits of Saint-Bauzile (Ardèche) in southern France indicate the presence of a gliding membrane. This species appears to be a distant relative of the Japanese Dormouse (Glirulus japonicus), which is a non-gliding arboreal rodent and the only surviving member of this genus that lives in the montane forests of Japan. The anatomy of the fossil glider differs slightly from living forms by the proportions of the segments of the limbs and the greatly elongated bushy tail which is typical of gliding mammals of that size.

Another extinct glider with no subsequent gliding relatives is from the extinct rodent Family Eomyidae, which once had a wide distribution in North America, Europe and Asia. The modern rodent groups that are most closely related to this family include the New World pocket mice (Family Heteromyidae) and the pocket gophers (Family Geomyidae). So far, the only gliding species found of this family is the early or dawn mouse Eomys quercyi from Oligocene deposits in Quercy in southern France.

When described in 1987, it was not at first recognised as a gliding species, and it was not until 1996, after a well-preserved specimen was discovered from Oligocene deposits in Enspel, Germany, that it was identified as a glider. Eomys quercyi was approximately 20 centimetres in length, with its gliding membrane having a low wing loading thus giving it a manoeuvrability which allowed slow glides in densely forested areas where there is little air turbulence. Abundant fossils of leaves, fruits and seeds where the rodent was found suggest it inhabited a thick mesophytic forest, which was widespread in western and central Europe during the late Oligocene.

In 2006 another extinct species of gliding mammal, Volaticotherium antiquus or ‘ancient gliding beast’, was discovered from Inner Mongolia. This incredibly strange creature is so unusual that it has no known relatives and has been placed in its own family known as the Volaticotheriidae within a new Order of mammals, called the Volaticotheria.

This species is also the oldest species of gliding mammal ever found. It extends the earliest record of gliding for mammals to the Cretaceous some 125 mya. This is 75 million years older than any previously discovered gliding mammal. Volaticotherium antiquus was the size of a squirrel and had an estimated body mass of about 70 grams, similar to that of the modern Southern Flying Squirrel from the United States of America.

A fourth species of extinct mammal that has been proposed to be a glider is an undescribed marsupial from Palaeocene deposits (65–56 mya) in Brazil. The conclusion that this species was a glider was derived from features of the humeri and femora including its exceptionally long and slender structure, similar to living gliding mammals.