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Oldest Skeleton of a Fossil Flying Squirrel Casts New Light on the Phylogeny of the Group

Penelitian - Scientists report the oldest fossil skeleton of a flying squirrel 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.

Phylogenetic analyses combining morphological and molecular data generally support older dates than previous molecular estimates, being congruent with the inclusion of some of the earliest fossils into this clade and show that flying squirrels experienced little morphological change for almost 12 million years.

Penelitian Oldest Skeleton of a Fossil Flying Squirrel Casts New Light on the Phylogeny of the Group

Mammals can walk, hop, swim and fly, a few, like marsupial sugar gliders or colugos, can even glide. With 52 species scattered across the Northern hemisphere, flying squirrels are by far the most successful group that adopted this way of going airborne.

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. Tiny specialized wrist bones, which are unique to flying squirrels, help to support the cartilaginous extensions.

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. However, the dental features used to distinguish between gliding and non-gliding squirrels may actually be shared by the two groups.

Isaac Casanovas-Vilar of the Universitat Autònoma de Barcelona and colleagues describe the 11.6 million years old fossil. The wrist bones reveal that the animal belongs to the group of flying squirrels that have large sizes.

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.



In addition, the results show that Miopetaurista is closely related to Petaurista, a modern group of giant flying squirrels. 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.

Molecular and paleontological data are often at odds, but this fossil shows that they can be reconciled and combined to retrace history. Discovering older fossils, or even transitional forms, could help to retrace how flying squirrels took a leap from the rest of their evolutionary tree.

Journal : Isaac Casanovas-Vilar et al. Oldest skeleton of a fossil flying squirrel casts new light on the phylogeny of the group, eLIFE, Oct 9, 2018, DOI:10.7554/eLife.39270

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