LIFE × EVOLUTION

The Origin of Feathers

~240 to 160 million years ago

Phanerozoic · Mesozoic · Triassic

Feathers appeared on animals that could not fly, between about 240 and 160 million years ago, and a single network of genes builds scales, feathers and hair.

Feathers are the skin covering of birds. They occur on animals incapable of flight, so their origin is separate from flight, their best-known function. A single network of developmental genes, the genes that act while the body of the embryo forms, builds scales, feathers and hair. Scales, feathers and hair are therefore variants of one another. Pan and colleagues (2019) analysed the proteins of a dinosaur feather from the Jurassic period. Feathers are made of keratins, a family of proteins. The Jurassic feather consists of a softer mixture than a modern feather. It is richer in alpha keratin and poorer in beta keratin, the form that gives a flight feather, a long feather of the wing or tail, its stiffness. The shift towards the stiffer composition accompanies the transition from dinosaur to bird.

Why it matters

According to the classic account, a structure evolves towards the function it performs today. Feathers contradict that account. They served first for insulation, display and touch, and the stiffer composition used in flight came only afterwards. Hair probably appears at the same period in the mammal lineage. The lineage with feathers and the lineage with hair both show evidence of a higher metabolism, the rate at which the body uses energy, at the moment when life on land was rebuilding after the end-Permian catastrophe, a mass extinction.

Dating & uncertaintyDisputed

Researchers report filaments in dinosaurs remote from the bird lineage and in pterosaurs, the flying reptiles. If the filaments are feathers, feathers are eighty million years older than birds. If the filaments are another structure, feathers are not that old. The fossils are too incompletely preserved to decide between the two readings.

Earth history as one day

22:43:521 h 16 min before midnight

if Earth’s 4.54 billion years were compressed into a single day