However, flying squirrels are currently recognized as a monophyletic clade, as supported by a set of synapomorphies in the wrist ( Thorington, 1984). The fact that presumed fossil flying squirrels are at least as old as (or maybe even older than) the oldest tree squirrels (36.6 – 35.8 Ma) may support the latter hypothesis. They have been classically regarded as a distinct subfamily among the Sciuridae ( McKenna and Bell, 1997 McLaughlin, 1984 Simpson, 1945), and even sometimes considered a separate family derived from a different group than the remaining sciurids ( De Bruijn and Ünay, 1989 Forsyth Major, 1893 Mein, 1970). Discovering older fossils, or even transitional forms, could help to retrace how flying squirrels took a leap from the rest of their evolutionary tree.įlying squirrels (Sciurinae, Pteromyini) are the only group of gliding mammals to have achieved a significant diversity (52 species in 15 genera) and wide geographical distribution across Eurasia and North America ( Koprowski et al., 2016). Molecular and paleontological data are often at odds, but this fossil shows that they can be reconciled and combined to retrace history. In fact, their skeletons are so similar that the large species that currently inhabit the tropical and subtropical forests of Asia could be considered living fossils. In addition, the results show that Miopetaurista is closely related to Petaurista, a modern group of giant flying squirrels. Evolutionary analyses that combined molecular and paleontological data demonstrated that flying squirrels evolved from tree squirrels as far back as 31 to 25 million years ago, and possibly even earlier. The wrist bones reveal that the animal belongs to the group of flying squirrels that have large sizes. describe the 11.6 million years old fossil, the oldest ever found. From the mud emerged the minuscule specialized wrist bones: the primate-turned-rodent was in fact Miopetaurista neogrivensis, an extinct flying squirrel. As the specimen – nearly an entire skeleton – was being prepared, paleontologists insisted that all the ‘dirt’ attached to the bones had to be carefully screen-washed. In fact, and much to the disappointment of paleoprimatologists, further excavating revealed that it was a rodent. ![]() In 2002, the digging of a dump site in Barcelona unearthed a peculiar skeleton: first a tail and two thigh bones, big enough that the researchers thought it could be the fossil of a small primate. However, recent studies show that the dental features used to distinguish between gliding and non-gliding squirrels may actually be shared by the two groups. The origin of flying squirrels is a point of contention: while most genetic studies point towards the group splitting from tree squirrels about 23 million years ago, the oldest remains – mostly cheek teeth – suggest the animals were already soaring through forests 36 million years ago. Tiny specialized wrist bones, which are unique to flying squirrels, help to support the cartilaginous extensions. To drift from tree to tree, these small animals pack their own ‘parachute’: a membrane draping between their lower limbs and the long cartilage rods that extend from their wrists. With 52 species scattered across the Northern hemisphere, flying squirrels are by far the most successful group that adopted this way of going airborne. Mammals can walk, hop, swim and fly a few, like marsupial sugar gliders or colugos, can even glide. They also show that flying squirrels experienced little morphological change for almost 12 million years. Our phylogenetic analyses combining morphological and molecular data generally support older dates than previous molecular estimates (~23 Ma), being congruent with the inclusion of some of the earliest fossils (~36 Ma) into this clade. Here we report the oldest fossil skeleton of a flying squirrel (11.6 Ma) that displays the gliding-related diagnostic features shared by extant forms and allows for a recalibration of the divergence time between tree and flying squirrels. Therefore, fossils attributed to this clade may indeed belong to other squirrel groups. Thus far, identification of extinct flying squirrels has been exclusively based on dental features, which, contrary to certain postcranial characters, are not unique to them. However, their evolutionary story is not well known. ![]() Flying squirrels are the only group of gliding mammals with a remarkable diversity and wide geographical range.
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