Most people would associate feathers with birds; if one were to describe a bird, the first thing one would say is: “they have feathers”. However, China has recently wielded many fossils of non-avian dinosaurs that have feathers, proving that feathers are strictly not for birds.
It appears that coelurosaurian theropods, non-avian, had feathers. These dinosaurs were relatively small, about 3m maximum, which lived through the mid-Triassic to Early Jurassic. Below is a diagram showing the relationship between archosaurs, namely dinosaurs. As you can see, ‘Coelurosauria’ is seen a couple of nodes before ‘Aves’- birds.
So if feathers aren’t specifically for birds alone, where did they come from? And who grew them first?
For starters, it must be said that feathers might not have evolved first for flight. Theropod dinosaurs’ arms were too short and their bodies were too heavy for powered flight. Also, the first feather was not a typical feather that we would think of- it was more a wiry fuzz that we could perhaps see on baby birds today. They might have first adapted for protection; for camouflage; for insulation or for sexual display, we’re not really sure. It took many millions of years for feathers to evolve from small wiry fluff to the complex and long feathers found on modern birds. Below is a proposed hypothesis of the stages of feather evolution. As you can see, feathers started off to be one strand, then began to branch.
Early birds, such as Archaeopteryx still contained some reptile-like features, such as simply teeth, a long bony tail and claws. Reptiles also have scales. Dinosaurs too have scales, so it is possible that these flat scales started to stretch out, maybe even fray and become feathers. If these small dinosaurs needed to run around a lot, feathers on their arms and flapping would give them momentum. This is another idea as to how feathers developed.
Furthermore, small dinosaurs that lived in a harsh environment, filled with nooks and crannies would benefit from powered flight. It takes a lot of energy and time to climb from rock to rock, so developing a way to glide, even fly, would be a much easier mode of transportation. This is definitely a main theory behind pterosaur (sister taxon to dinosaurs) flight.
So already we have two disputing ideas; feathers were evolved for social or sexual reasons or feathers were created to assist gliding through a tough terrain. But which is right?
To make this decision, we must look at the facts for both arguments and deduce from there. First, we will look at the ‘feathers for flight’ argument. In the 70’s, palaeontologist John Ostrom noticed many similarities between theropod dinosaurs, such as Velociraptor, and birds. For example, they both have wish bones. Ostrom concluded from this that birds were indeed the living representatives of theropod dinosaurs.
A following discovery in 1996 superficially supported this theory; the fossil of Sinosauropteryx was found in China, containing a layer of thin, hollow filaments covering its tail and back- primitive feathers. This may at first seem like a ‘missing link’ between feathered birds and dinosaurs but, feathers down the animals back suggest that feathers were not for flight. (Cool fact, Sinosauropteryx was venomous).
Soon, many fossils of feathered theropods were being found and soon a detailed story of the feather was beginning to be pieced together…
First came simple filaments. Then, different theropod groups evolved different types of feathers; some fluffy, some had symmetrical barbs, some had stiff ribbons and some had broad filaments. These broad, hollow filaments can be found on modern baby birds. Fossil evidence also shows that feathers had bright colours, such as reds and blues. This could have been for display, like peacocks. Also, Gigatoraptors have been found in death position sheltering their nests. Their feathers could have been to insulate and keep their eggs warm.
So once we decide for ourselves why feathers were first invented, we come back to the question: who had them first? In 2009, in China (again), a bristly-backed creature, Tianyulong was discovered. (Image below) This dinosaur comes from the ornithischian branch of the dinosaur family tree, very far away from the theropod branch. So, could the ancestor of all dinosaurs have bristles? Moreover, does that mean that some dinosaurs secondarily lost their feathers? Pterosaurs also contain ‘fuzz’- could the ancestor that led to dinosaurs and pterosaurs also have fluff?
I know I haven’t really answered the question: where do feathers come from? But to be quite honest with you, no one really knows. As new discoveries of our feathered friends come out of China, we will unravel the history even more. Now people are beginning to think that the origin of the feather goes back into the archosaurs that even alligators might have had them! (Sceptical? I am). To conclude…watch this space!