A new study of ancient feathers adds weight to the theory that primitive birds, close relatives of feathered dinosaurs, were less versatile fliers than their modern descendants. (Photo : (Illustration by Carl Buell, courtesy Jakob Vinther/Bristol University)

Prehistoric birds possessed a more primal version of wings as compared to modern birds, a new study reveals.

A team of international researchers studied the fossils of prehistoric Jurassic bird Archaeopteryx lithographica and the feathered dinosaur Anchiornis Huxley. Archaeopteryx lithographica lived around 155 million years ago and is touted to be the earliest known bird, which carries a combination of dinosaur and bird characteristics.

Upon close examination of the fossils, the research team found that the wings of the prehistoric bird and the bird-like dinosaur were different from those of modern birds. The birds had multiple overlapping layers of long wing feathers that were difficult to separate, in contrast to modern birds, which have a single primary layer of long feathers that can be easily separated. Short feathers were found to lie on top of the long feathers.

The wing structures of these prehistoric birds suggest that it would have been difficult for them to liftoff from the ground or carry out low-speed flight. Instead, these birds could have possibly climbed trees and used their wings to produce strong airfoils for gliding from a height or indulging in a flapping flight, researchers said.

Although the wing feathers of both Anchiornis Huxley and Archaeopteryx lithographica have similarities, they are not the same. While Archaeopteryx had multiple layers of long flight feathers, Anchiornis had strip-like feathers that overlapped. The only bird today that has something remotely similar to the wing feathers of Anchiornis is the penguin.

The difference in the wing structure of the ancient birds represents "early experiments in the evolution of the wing." Moreover, the dissimilarities between the wing feathers of the early and modern birds shed light on the origins of wing design, researchers noted.

"We are starting to get an intricate picture of how feathers and birds evolved from within the dinosaurs," co-author Jacob Vinther, from University of Bristol in the United Kingdom, said in a statement.

"We now seem to see that feathers evolved initially for insulation. More complex vaned or pinnate feathers evolved for display. These display feathers turned out to be excellent membranes that could have been utilized for aerial locomotion, which only very late in bird evolution became what we consider flapping flight," he said.

The findings of the study, "Primitive wing feather arrangement in Archaeopteryx lithographica and Anchiornis huxleyi", are published in the journal Current Biology.