It has been decades since we received the astonishing news that dinosaurs – some of the largest and most fearsome creatures ever to have roamed our Earth – were actually covered in feathers.

But exactly how these feathers looked – and how the biological structures ultimately became those we see on our feathered friends now – has been something of a controversial topic of debate amongst scientists ever since the news first dropped.

And now two researchers from the University of Geneva (UNIGE) have unveiled the clearest picture yet of how dinosaurs’ proto-feathers became the soft and vibrant feathers we know today.

Feathers are fundamental for the survival and life processes of birds. They are responsible for everything from insulating and waterproofing the bird, to assisting in their communication and mating rituals. And that is not to mention flying, which would be impossible without a bird’s feathery wings.

But exactly how proto-feathers became these crucial and often ostentatious displays of plumage remained a question mark until the University of Geneva’s Michel Milinkovitch and Rory Cooper began their observations of the embryonic development of chickens.

And what they discovered, in their research which was recently published in the journal PLOS Biology, is a ground-breaking stepping stone toward a firm and certain answer about feather development.

The pair – specialists in molecular signalling pathways – discovered that scales, hair, and feathers develop thanks to specific signals sent along these pathways, and in particular, one curiously known as the Sonic Hedgehog (Shh) pathway.

And in their previous studies, the Swiss researchers proved that by injecting pathway-activating molecules into chicken embryos, scales on a bird’s feet can be transformed into feathers. This proved that the Shh pathway was crucial to the development of these kinds of structures.

So, to understand this evolutionary change, the researchers turned the tables on their experiment to understand what would happen if the Shh pathways were prevented from sending their messages, as Rory Cooper noted in a statement:

‘‘Since the Shh pathway plays a crucial role in feather development, we wanted to observe what happens when it is inhibited.’’

And, surprisingly, they found that the result was buds on the chicken’s skin that in many ways resembled proto-feathers.

However, the feather development did not prove to be fully inhibited, with just some patches of these follicles present on the chicks, as Michel Milinkovitch continued:

‘‘Our experiments show that while a transient disturbance in the development of foot scales can permanently turn them into feathers, it is much harder to permanently disrupt feather development itself. Clearly, over the course of evolution, the network of interacting genes has become extremely robust, ensuring the proper development of feathers even under substantial genetic or environmental perturbations. The big challenge now is to understand how genetic interactions evolve to allow for the emergence of morphological novelties such as proto-feathers.’’

Though the chickens ultimately developed to have the feathers that evolution intended, their temporary inhibition of growth was crucial to the researchers.

It showed a reversal – albeit a temporary one – of the process that feathers have followed to develop into what we know now.

And that gives scientists an even greater insight into what kind of feathers the dinosaurs might have had.

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