Feathers Through Time

How did feathers evolve? From the fossil record, we know that birds evolved from dinosaurs, some of which had feathers. But those first feathers had nothing to do with flight—they probably helped dinosaurs show off, hide, or stay warm. Scientists recently worked out a hypothesis to explain how complex flight feathers could have evolved. They probably began as simple tufts, or so-called “dino fuzz”, and then gradually developed into interlocking structures capable of supporting flight.

Explore our interactive feather evolution cartoon to learn more about how “dino fuzz” evolved into elegant flight feathers.

Where Did Feathers Come From?

This songbird is covered in feathers that help her stay warm and dry, to hide or show off, and to fly. But how and why did these feathers evolve? What were the first feathers like, and on what kinds of creatures did they grow?

The First Clue: Fossilized Feathers

To piece the puzzle of feather evolution together, scientists study modern feathers and fossilized traces of ancient feathers. The first major clue was Archaeopteryx, unearthed in Germany in 1861. Perhaps the most famous fossil find of all time, the Archaeopteryx specimen is 150 million years old and contains impressions of feathers that look like modern flight feathers—asymmetric in structure with interlocking branches.

Clues from Feather Growth

Biologists reasoned that the Archaeopteryx specimens were not the first feathers—there must have been a series of simpler feathers that preceded full-blown flight feathers. Evolutionary biologists often look to a structure’s growth pattern for clues to its evolutionary past. Watch the growth process and set yourself up for understanding the innovations that occurred during the evolution of flight feathers.

• Tubular sheath forms
• Branches begin forming
• Branches fuse into central shaft
• Sheath disintegrates
• Feather unfurls

The Evolution of Flight Feathers

Careful study of feather growth inspired scientists to propose the following evolutionary hypothesis. Stage 1: The first feathers were flexible hollow tubes.

The Evolution of Flight Feathers

Stage 2: These simplest feathers then evolved into clusters of hollow tubes, or barbs. Structurally, this stage is similar to the point early in the growth process when the barbs have formed but before they start to fuse into a central shaft.

The Evolution of Flight Feathers

Stage 3a and b: Then side branches, or barbules, developed and bases of the barbs fused together into a central shaft, or rachis. We don’t know which of these innovations came first, but both features were necessary in the evolution of the modern flight feather.

The Evolution of Flight Feathers

Stage 4: The next innovation was the development of small hooks on the barbules that interlock like Velcro to create a smooth surface, or vane, on either side of the central shaft.

The Evolution of Flight Feathers

Stage 5: And finally, feathers evolved asymmetric vanes that support flight by creating a strong leading wing edge. This type of feather was already evident on Archaeopteryx and is what we find on the wings of most modern birds.

Dino Fuzz

Evidence supporting this evolutionary hypothesis has been mounting. In the past 15 years a series of feather traces have been discovered on dinosaur fossils from the Yixian formation in China and in amber from western Canada. We don't think of dinosaurs as being covered in feathers, but dozens of theropod dinosaurs had simple stage 1 and 2 feathers. The scientific community has dubbed these feathers “dino fuzz” and it is likely that some ferocious tyrannosaurs were covered in fuzz—perhaps as an insulating layer.

Displaying Dinos

Some theropod dinosaurs had more than simple fuzz and were adorned with feathers from later evolutionary stages. Ornithomimus for example had large feathers anchored to wing like appendages. But since they only grew on the massive adults, these feathers were likely used for display rather than flight.

Early Feather Functions

In recent years, fossils matching all of the proposed stages of feather evolution have been discovered. What‘s clear is that early feathers were not capable of supporting flight. Whether used for camouflage, insulation or display, ancient feathers evolved through a series of innovations to form the modern flight feather whose evolutionary legacy is etched in its growth process.

Feathers Evolved First on Dinosaurs

So when admiring the plumage on a modern songbird, just remember those feathers began as humble “dino fuzz”.