Over the past few years, we’ve heard gathering evidence that dinosaurs were not the cold-blooded, scaly-skinned beasts of the past, but fluffy, feathered, and brightly colored. Well, a new study published in Biology Letters seems to suggest that they might have been more right to begin with, and that most dinosaurs probably didn’t have feathers.

By examining the fossil record of dinosaur skin impressions preserved in rock, researchers from the Natural History Museum, London, have concluded that feathers were far less prevalent than previously believed. Whilst they certainly covered many of the carnivorous dinosaurs, such as velociraptors and tyrannosaurus, the suggestion that some of the larger herbivores were also clad in downy feathers is probably wrong.

“Most of our analyses provide no support for the appearance of feathers in the majority of non-avian dinosaurs,” says Professor Paul Barrett, who co-authored the study. “Although many meat-eating dinosaurs were feathered, the majority of other dinosaurs, including the ancestor of all dinosaurs, were probably scaly.”

It’s fairly well accepted that many theropod dinosaurs, the ones that eventually gave rise to birds, were no doubt covered in what are called “protofeathers.” But some recent discoveries of larger herbivores that also appear to be covered in these feather-like filaments have raised the question of whether the last common ancestor to all dinosaurs was also fluffy. Are feathers in dinosaurs the norm rather than the exception?

Well, by looking at which beasts were downy and which weren’t, and then building an evolutionary tree of how they all related to each other, the scientists discovered that it was most likely that the majority of the dinosaurs were covered in scales, and feathers only evolved in the theropods. But what about the few, stray herbivores that seem to have been covered in quills? It’s possible that those odd exceptions were probably experimenting independently.

“As palaeontologists we are at the mercy of available data, which given the interest in the field are ever changing,” explained Nicolàs Campione, another of the researchers. “Our study shows that dinosaurs experimented extensively with their 'outer look' and potentially independently along separate evolutionary lineages. That is what the data allow us to say at present.”

As dinosaur biology is a hotly debated and hugely competitive area of research, the team working on this study suspect there might be a few vocal objections to their finding, but they accept that this is how science works. “This is a hypothesis that can only be tested with the discovery of new fossils with preserved skin or feathers. In particular, we need fossils that fill key locations in the evolutionary tree of dinosaurs,” says Campione.