In both types of feather, the barbules that extend from the barb ramus grow from a single layer of cells, called the barbule plate, on the periphery of the barb ridge.
A discovery of 115 million-year old fossils in Siberia indicates that feathers were much more widespread among dinosaurs and developed much earlier than have been thought.
How all these creatures survived those conditions was, Dr Druckenmiller suggests, a consequence of dinosaurs' warmbloodedness and the downy feathers many of them are now known to have sported.
In Emily Dickinson's poetry: " Hope is the thing with feathers, that perches in the soul." Dickinson likens hope to a bird that continues to sing within us, emphasizing its resilience and perseverance.