Three discoveries changed how dinosaurs look
Our visions of smooth and scaled dinosaurs – as we know them from the Jurassic Park films – is being superseded by increasing evidence of feathers being found all over the dinosaur family tree.
Tyrannosaurus rex was a fluffy killer
1 Scientists used to think that bigger dinosaurs would not have had feathers, since large animals do not lose heat as easily as small ones. Then in 2012 a 9-metrelong T. rex ancestor, Yutyrannos, which existed some 125 million years ago, was discovered in China. The big predatory dinosaur had primitive fluffy feathers, and though no featherlike structures have yet been found on any T. rex, there is every likelihood that it also had some kind of feathers.
Raptor feet were covered in feathers
2 While it turns out that feathers cannot originate from scales, the opposite is possible. Small predatory dinosaurs are often portrayed with scaly feet, but fowls (chicken, ducks and geese, the closest modern dinosaur relatives) have two types of scales on their feet: small, round, reptile scales and bigger scales that developed from feathers. Fossils from Liaoning, China, indicate that some raptors even had feathers on their toes.
Triceratops had bristles
3 Palaeontologists had long been convinced that the big horned Triceratops dinosaur had neither hair nor feathers. But as it is related to the much smaller Psittacosaurus, which we now know to have had long bristles on its tail, they are no longer so sure. An impression of the Triceratops’ skin indicates that it might have had similar bristles. Scientists are less certain, however, whether the bristles have anything to do with feathers.
Dr. David Unwin from the University of Leicester in the UK is a pterosaur expert, and he denies that pterosaur wings were covered in a type of feathers. He emphasises the discovery of some 30 pterosaurs, several of them with well-preserved wings, yet all naked and smooth. On the other hand, the wing membrane includes structures that, in a state of decay, could be misinterpreted as ‘fluffy’ and feather-like under a microscope. The lack of knowledge of decay processes is a major current problem, according to David Unwin, as it makes palaeontologists’ efforts to identify structures in the fossils prone to error. These relics have spent millions of years deep in the ground, being both compressed and heated.
Professor and dinosaur evolution expert Paul Barrett from the Natural History Museum in London has contributed to a new book about the origin of feathers. He and two other scientists have worked with computer modelling and probabilities, trying to calculate backwards towards the first feathers.
The scientists fed the computers data relating to 77 dinosaur species that have been found with well-preserved skin showing traces of scales, hair, or feather-like structures. The dinosaurs were placed on a family tree, and in the places where fossils are missing, the scientists inserted hypothetical fossils. In one model, they placed a pterosaur with protofeathers; in another model, they used a pterosaur without feathers. In this way, they could predict different lines of development and calculate the likelihood of the hypothetical lines being the true ones.
The models revealed that any common ancestor of dinosaurs and pterosaurs is highly unlikely to have had feathers.
“I had expected that models based on a pterosaur with protofeathers would result in all dinosaurs having feathers. It surprised me that that was not the case,” Paul Barrett says.
Plumed piece is missing
The results of the computer models reveal that in spite of the many finds made in recent years, we still lack important information. And although the study denies a plumed common ancestor, Paul Barrett thinks that this could change.
“It is still possible that feathers played an important role in the history of dinosaurs. And just one or a few finds of early dinosaurs or dinosaur relatives with feathers would change our approach considerably,” he says.
The ancestor of all dinosaurs originated in the Triassic 251-200 million years ago, and according to palaeontologist Bent Lindow from the Natural History Museum of Denmark, it would require immense luck to find a feather from such an ancient beast.
“It is difficult to find such old fossils, as very special conditions are required to preserve soft tissue,” he says. “But it is not impossible – and we can begin by looking specifically for them.”
The closest relatives of birds, dinosaurs, and pterosaurs are crocodiles, as they all belong to the group of archosaurs. The first crocs originated in the Triassic, and although they do not have feathers, the ability to develop plumage is in the genes of modern crocodiles.
So perhaps somewhere a fossil of some remote plumed crocodile relative is hiding in the ground, waiting to be found – just like Sinosauropteryx 25 years ago. Just one single feather may be all we need.