A Feathery Pedigree

Image: Scansor chick, Matt Martyniuk, 2014, creative commons attribution license 3.0

A feathered, finch-sized tree-climber that lived 164 million years ago in Liaoning, China may force a rewrite of the textbooks.

It has long been believed that modern birds evolved from ground-dwelling dinosaurs which had developed the power of flight. But Scansoriopteryx (Latin for "climbing wing"), wasn't a dinosaur - it came from a much more ancient lineage, and was a tiny tree-climbing creature with the ability to glide, much like modern flying squirrels.

According to University of North Carolina paleontologists Stephen Czerkas and Alan Feduccia, Scansoriopteryx had been mistakenly classified as a ground-dwelling theropod (Greek for "beast foot") dinosaur, from which experts thought flying dinosaurs and eventually birds evolved.

Using 3D microscopy, high resolution photography and special lighting to reveal never-before-seen features of the fossil, the team found that Scansoriopteryx "unequivocally lacks" the skeletal features of a dinosaur. They add that this is further evidence that birds are not descended from dinosaurs, but from much tree-climbing archosaurs (Latin for "ruling reptiles"), an ancient lineage that long predated the dinosaurs, and would eventually also evolve into the crocodilians.

The fossil contains feather imprints and shows that Scansoriopteryx had an elongated third finger, nearly twice as long as its second - most theropod dinosaurs have an elongated second finger. Its bird-like feet and claws had been adapted for an arboreal (tree-dwelling) lifestyle, optimized for climbing and perching.

Scansoriopteryx also had several other distinctly birdlike features, such as wing- and hindlimb feathers, long forelimbs, wing membranes distal (opposite) to its elbow, but, rather than flying, it would only have been capable of gliding or parachuting from trees.

Although Czerkas and Feduccia's conclusions have drawn skepticism, the discovery apparently bears out early 1900s predictions that evidence would show modern birds are derived from tiny, tree-dwelling archosaurs with feathers for gliding. This "trees down" view contrasts with the "ground up" view long held by many modern paleontologists who say birds evolved from ground-dwelling theropod dinosaurs.

Source: "Birdlike fossil challenges notion that birds evolved from ground-dwelling dinosaurs", press release, July 9, 2014, Springer Science and Business Media