In “The belly of the beast: A chance discovery from China suggests some dinosaurs lived in trees” (Economist , Nov 12 2011), we learn that the remains of an as-yet unidentified bird have been found inside a species of (feathered) Microraptor from about 66 mya. The bird has a long third toe, which is inferred to mean,
The size of the prey’s third toe is important because, among birds, long third toes are helpful for grasping branches and perching in trees. Indeed, the trait is so useful for arboreal life that it is used by many avian palaeontologists to decide whether newly excavated species of fossil birds lived in trees or on the ground. And the last meal of this particular specimen of Microraptor did, indeed, have a long third toe.
That elongated toe suggests to Dr O’Connor that Microraptor, too, was arboreal, …
(which would explain how it caught the bird, presumably) … Paleontologists are divided as to whether birds had terrestrial or arboreal ancestors; the only contribution this find makes to the debate is
… it does suggest feathers may have helped promote life in the trees, even for creatures that could not actually fly.