Archaeopteryx could fly: a fossil reveals how its wings worked

Archaeopteryx could fly, and an exceptionally preserved fossil is helping scientists understand how its wing worked in the air. In roughly 150-million-year-old limestone, the specimen preserves an almost complete skeleton together with traces of skin and feathers that had never been seen this clearly in Archaeopteryx.

Archaeopteryx is famous for its unusual combination of features. It had teeth, clawed fingers and a long bony tail inherited from its dinosaur relatives, yet it also possessed wings and well-developed feathers. For more than 160 years, its fossils have provided a window into the early evolution of birds.

The specimen now housed at Chicago’s Field Museum is the fourteenth Archaeopteryx described scientifically. It is nearly complete and relatively uncrushed. In the Nature study, researchers examined it using computed tomography, ultraviolet illumination and detailed anatomical comparisons.

Feathers that had never been seen before

The most intriguing feature appeared on the wings.

The fossil preserves long feathers along the upper portion of the wing, known as tertials. In living birds, these feathers help cover the space between the body and the main flight surface of the wing.

That matters because Archaeopteryx had a relatively long upper-arm bone. Without additional feathers, a substantial gap could have existed between the body and the main flight feathers. Air passing through such a gap would reduce the wing’s ability to generate lift.

The tertials filled this space, allowing the plumage to form a more continuous aerodynamic surface.

This is particularly important because closely related non-avian dinosaurs do not show the same arrangement of long feathers along the upper arm. The authors therefore interpret these feathers as an adaptation associated with flight.

This is not the first evidence that Archaeopteryx could become airborne. Previous research on its wing and bone geometry had already supported some capacity for powered flight. The Chicago specimen adds another piece of evidence by showing how the feathers themselves could have completed a functional wing surface.

More than feathers

The fossil also preserves valuable information from the skull, vertebral column, hands and feet.

The palate has an anatomy intermediate between some non-avian dinosaurs and more derived birds. This fits with a gradual evolutionary transition from a relatively rigid theropod skull toward the more mobile skull architecture found in birds. In modern birds, parts of the upper jaw can move relative to the braincase, allowing the beak to function in a wide variety of ways.

Skin traces on the hand suggest that one of the smaller fingers retained some mobility. The foot pads, meanwhile, appear better suited to ordinary terrestrial locomotion than to grasping prey with specialized raptorial feet.

The phrase “soft tissues” also needs some care. It does not mean that ordinary skin or intact cells survived for 150 million years. What remains are fossilized traces of structures that were once soft. Ultraviolet light helped reveal these subtle features because of the unusual preservation chemistry of the Solnhofen limestone fossils.

What the fossil can — and cannot — tell us

A single fossil cannot tell us how fast Archaeopteryx flew, how far it could travel or how long it could remain airborne. An aerodynamically functional wing provides evidence about flight capability, not a complete record of the animal’s behaviour.

Nor should Archaeopteryx be imagined simply as an animal halfway through turning into a modern bird. Bird evolution was a branching process involving many feathered dinosaurs with different combinations of anatomical features. Archaeopteryx represents one early version of that evolutionary experiment.

Claims that this fossil has once again “proved Darwin right” make for an eye-catching headline, but they oversimplify the science. Its real contribution is more specific and more interesting.

A 150-million-year-old animal has preserved a small but crucial feature: feathers that closed the gap in its wing. Details like these allow palaeontologists to reconstruct, step by step, how the feathered forelimbs of dinosaurs became effective avian wings.