Bright ideas Why birds evolved into colourful show-offs
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It opens the door to many new discoveries of dazzling displays in fossil birds and other dinosaurs
Dr Jakob Vinther
SCIENTISTS have gained new insights into how birds evolved to have colourful feathers, thanks to Bristol research.
Iridescence is responsible for some of the most striking visual displays in the animal kingdom, and a new study of feathers from almost 100 modern bird species has helped uncover how this colour diversity evolved.
The phenomena of iridescence refers to colour changes when an object is viewed from different angles.
Melanosomes are animal cell structures responsible for trapping, synthesising, storing and moving the lightabsorbing pigment melanin, and are responsible for colour and protection from sunlight.
A team of University of Bristol researchers used scanning electron microscopy to quantify melanosome extracts from the feathers of 97 species of modern birds with iridescent plumage, taken from the collections of the Zoological Museum of Copenhagen.
The study showed that iridescent feathers contain the most varied melanosome morphologies of all types of bird coloration sampled to date.
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 mela- nosomes to achieve ever greater diversity in colour.
“I wanted to find out if we could improve current predictive models for fossil colour based on melanosome morphology by including all types of melanosomes found in iridescent feathers.”
Dr Jakob Vinther, co-author of the study and a leading researcher in the field of paleocolour at Bristol’s School of Biological Sciences, 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.
“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.”