Plumage pattern revealed in 150 million-year-old bird
According to new findings, bird ancestors first evolved a shiny plumage about 150 million years ago, when feathered dinosaurs began climbing trees.
Scientists say this meant they were protected from predators and could focus on developing iridescent plumage to attract one another.
Some of the most striking visual displays in the animal kingdom are caused by iridescence, which refers to colour variations when an object is viewed from various angles.
To figure out how this colour diversity evolved, researchers compared feathers from nearly 100 modern bird species to fossilized species.
Melanosomes are animal cell structures responsible for trapping, storing and moving the light-absorbing pigment melanin. They are also responsible for colour and protection from sunlight.
‘Many birds have iridescence – such as the hummingbird or magpie – and we have been studying how iridescence is created’, Dr Jakob Vinther, co-author of the study and a leading researcher in the field of pale colour at Bristol’s School of Biological Sciences, told MailOnline.
By looking at fossilised melanosomes, researchers found that dinosaurs started getting shiny feathers around 150 million years ago.
‘There is a massive expansion of melanosome shapes that make all these remarkable colours.
Dr Vinther believes they were probably not as shiny as they are today but they were still iridescent.
‘I think it probably evolved because dinosaurs started to go up into the trees, which made them more safe from predators’, Dr Vinther said.
‘This meant their feathers could become more colourful to attract mates. ‘The ones on the ground would have had typical brown colours.
‘The more exposed you are the more vulnerable you are. The first dinosaurs couldn’t fly so they would have had a bad chance of survival if their feathers were iridescent.’
University of Bristol researchers used scanning electron microscopy to quantify melanosome extracts from the feathers of 97 species of modern birds with iridescent plumage, according to the research published in Evolution.
The feathers were taken from the collections of the Zoological Museum of Copenhagen.
The study showed that iridescent feathers contain the most varied melanosome shapes of all types of bird coloration sampled to date.
‘There has been an expansion to become more colourful up until today’, Dr Vinther said.
‘Perhaps 100,000 years or one million years from now birds will have even more beautiful feathers’, he said.
Unlike black, grey and brown feathers that always contain solid melanosomes, iridescent feathers can contain melanosomes that are hollow and/or flattened.
Lead author Klara Norden, who conducted the study during her undergraduate years at Bristol’s School of Earth Sciences, said: ‘It is already known that structural coloration is responsible for 70 per cent of the colour variability in birds.
‘These two facts might be coupled – birds evolved varied forms of melanosomes to achieve ever greater diversity in colour.
Ms Norden wanted to find out if it was possible to predict what the plumage of fossilised avian ancestors would have looked like based on the shape of the their melanosomes.
Dr Vinther had already collected the perfect fossil samples to test the new model on.
He said: ‘We had sampled Scania Cypselus, related to modern tree swifts, and Primotrogon, ancestor to modern trogons.
‘These groups are iridescent today and have flat and hollow melanosomes. Did their 48-million-year-old ancestors from Germany also have iridescent plumage?’
The model predicted that Primotrogon probably was iridescent, but it used solid rather than hollow melanosomes, unlike its modern descendants, meaning it would not have been as shiny.
‘This demonstrates how we now have the tools to map out the evolution of iridescence in fossil lineages,’ said Ms Norden.
‘It opens the door to many new discoveries of dazzling displays in fossil birds and other dinosaurs.’