Feather Evolution: How did feathers evolve?

Flight feathers, with their intricate microstructure, are impressive examples of natural engineering. But how did they 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.

Scientists recently worked out a hypothesishypothesisan explanation that is testable through study and experimentation to explain how flight feathers could have evolved.3 They probably began as simple tufts, and then gradually developed through stages of increasing complexity into interlocking structures capable of supporting flight.

Evolutionary stages:
Feather evolution stages illustration by Andrew Leach

1. The earliest feather was a simple hollow tube.

2. The simple tube evolved into a cluster of barbsbarbone of the main branches off the central shaft of a feather.

3. (a) The base of the barbs fused together to form a central rachisrachisRAY-kissthe stiff central shaft of a feather from which barbs branch and (b) barbulesbarbulebarb-YOOLone of the secondary branches off a feather barb branched from the barbs, as we see in modern-day down feathers.

4. The barbules evolved hooks that interlock to make flat vanes as in current contour feathers.

5. The feather structure evolved asymmetry with the aerodynamic properties of modern-day flight feathers.

Fossil evidence recently unearthed in China and Canada has confirmed that bird ancestors did indeed possess feathers from each of the steps in this proposed evolutionary pathway. Surprisingly, many theropodtheropodTHAIR-o-podbelonging to a bipedal subgroup of dinosaurs from which birds likely evolved dinosaurs had simple stage 1 feathers covering their bodies. This “dino fuzz” even covered close relatives of the great Tyrannosaurus rex. These early feathers may have been insulating, or when colorful, may have helped dinosaurs show off or stay camouflaged. There is also intriguing evidence of more complex Stage 3 and 4 feathers from finds like Ornithomimus edmontonicus. As adults, these large, bulky creatures sported feathers arranged along wing-like structures, but no wing feather traces have been found among the juvenile specimens. This suggests that even as dinosaurs started to evolve wings, the wing feathers were likely used for courtship or territorial display, not flight.4

Ancient feathers (dino fuzz) covering Yutyrranus in the Cretaceous period Illustration: Yutyrannus and other smaller dinosaurs from the Cretaceous by Brian Choo

Though it may take time for people to get used to the idea of fuzzy or elaborately plumed meat-eating dinosaurs, this scientific breakthrough reminds us that asking questions from multiple perspectives helps generate new testable hypotheseshypothesisan explanation that is testable through study and experimentation and scientific knowledge. For this reason, it is becoming more and more common for scientists to work across disciplines. In fact, the active field of evolutionary-developmental biologyevolutionary-developmental biology (evo-devo)a field of biology that investigates the relationship between an organism’s development and its evolutionary origins (“evo-devo”) focuses on discovering a structure’s evolutionary past by observing its process of growth and development.

Further Learning

aabb-xxl-icons-featuresNavigate a cartoon about feather growth and evolution to learn more about how “dino fuzz” evolved into elegant flight feathers
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