The discovery that all birds are dinosaurs is one of the greatest scientific achievements in recent years. This link has been illuminated by the unearthing of numerous feathered dinosaurs in China – previously unknown species whose bones have helped us map the evolutionary road from dinosaur to bird. These fossil finds have also helped researchers begin to understand one of the key characteristics that all birds share: feathers.
Though we once thought feathers evolved purely for flight, the fossil record shows us that many dinosaurs possessed ‘protofeathers’, feather precursors that were not actually capable of helping an animal to fly.
Most dinosaurs we know that possessed different types of feathers were on the evolutionary branch that gave way to birds. Known as theropods, the diverse group of ‘beast-footed’ bipedal dinosaurs includes the largest terrestrial carnivores, like the notorious T. rex. However, some other distantly related dinosaur cousins also possessed these strange filamentous structures. Some pterosaurs, the flying cousins of dinosaurs, even had a strange but similar fibrous coating over their bodies.
The discovery of protofeathers forced scientists to revisit some complicated questions: What caused feathers to evolve in the first place? What was their role? And were all dinosaurs feathered to some degree? Unfortunately for palaeontologists, the answers to these questions aren’t as nicely laid out as they would like – largely because the process of fossilisation can distort bone or hide details that would have been visible on a live animal (just because we don’t see feathers preserved on a fossil doesn’t mean that dinosaur didn’t have them).
So, what about DNA? Could DNA help shed some light on these questions? You’re probably thinking, ‘DNA isn’t preserved in fossils …’ and you’d be right for the most part. But it’s actually the DNA from modern, living dinosaurs (birds!) that can help us solve this mystery.
In a new study, a team of researchers led by Dr Craig Lowe attempted to crack open some of these riddles by comparing the genetic makeup of birds, alligators, turtles, lizards and a range of other animals. (It may seem like a random assortment of species, but all of these animals share a common ancestor with dinosaurs!) Through this genetic investigation, Lowe and his team were able to see just how far back in time specific genes key in the development of feathers could be found.
Amazingly, they discovered that the 'genetic toolkit' for feather making can be found nearly 150 million years before the oldest known birds flew and seems to line up with major shifts in evolutionary history. The evolution of the genes that control feather patterning, for example, seems to correspond with the development of the first hard-shell egg, in a group known as amniotes, which includes reptiles, birds and most recently … mammals like us! And keratin, a protein required to make feathers, first shows up with the origin of the archosaurs (the group that relates birds, dinosaurs, crocodiles and pterosaurs).
Palaeontologists have often speculated that all dinosaurs may have been feathered to some degree based on fossil evidence, but Lowe’s work proves the genetic tools for creating feathers were long in place even before the first dinosaur. In fact, 86 percent of genes regulating feather development may have been present long before. So, were all dinosaurs primitively feathered? We’re not sure yet. But the answers to these questions are likely buried deep beneath our feet … we just have to find them. This is exciting for palaeontologists, who now look forward to finding the most ancient ancestors of dinosaurs with some sort of proto-fuzz covering!
Top header image: Norma Desmond, Flickr
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