The colour displays of birds are one of the many wonders of the natural world. These displays are primarily involved in courtship behaviours by messaging reproductive fitness to potential mates. One of the more impressive feather colours is iridescence, which consists of multiple luminous colours that seem to change when seen from different angles. An example of this is observed in Ribbon Tailed Astrapias, from Papua New Guinea, which shows how iridescence can otherwise turn a black ordinary-looking bird into a vibrantly coloured one by changing from one angle to another .
These wonderful colours are generated from pigments and a variety of nanostructures that make up the feather. As coherent light scatters through crystal-like structures, called melanosomes, they produce iridescence , even a slight organization of these melanosomes can produce weakly iridescent colour. These nanostructures are diverse and have evolved independently numerous times in extant birds  and maybe even a little bit earlier.
Before 2012, the evolution of melanosomes and feather colour was unknown in dinosaurs. Till then, the only fossil evidence of iridescent plumage was limited to a 47-million-year-old isolated avian feather from Germany . That was until researchers in China found a well-preserved dinosaur specimen in one of the top global fossil hotspots, Jianchang County, western Liaoning Province. The specimen found was that of an early Cretaceous dinosaur named Microraptor.
To investigate potential feather colour, samples were taken from the Microraptor’s right forelimb and the melanosome structures compared with extant bird feathers. From this, it was found that the Microraptor had iridescent feathers most similar to the Brazilian teal duck. This discovery allowed for a conservative reconstruction of Microraptor with glossy black feathers with a slight iridescent sheen .
These findings found that dinosaurs and modern birds share iridescent colour and shed further light on the colourful world before the rise of Mammals. This pushed back the date of feather colour evolution by 73-103 million years from the Eocene back to the Cretaceous. It opened the possibility of more extinct feathered dinosaurs that were potentially just as colourful as the birds of today. Then in 2018, it was found that feather iridescence may have developed even earlier in the Late Jurassic, in a small theropod dinosaur called Caihong . The discovery of feathers and iridescence in specimens, such as Caihong and Microraptor, show a clear evolutionary pathway from the dinosaurs to the modern birds we have today.
Birds are famous for their amazing colours, yet these wonderful displays may have existed a few hundred millions before birds had even evolved.
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- “File:Dinosauria – Microraptor 02.jpg” by Tylwyth Eldar is licensed under CC BY-SA 4.0
- “Ribbon-tailed Astrapia Astrapia mayeri” by nik.borrow is licensed under CC BY-NC 2.0
- Prum, R.O., 2006. Bird Coloration, Vol. 1, Mechanisms and Measurements.
- Stoddard, M.C. and Prum, R.O., 2011. How colorful are birds? Evolution of the avian plumage color gamut. Behavioral Ecology, 22(5), pp.1042-1052.
- Vinther, J., Briggs, D.E., Clarke, J., Mayr, G. and Prum, R.O., 2010. Structural coloration in a fossil feather. Biology Letters, 6(1), pp.128-131.
- Li, Q., Gao, K.Q., Meng, Q., Clarke, J.A., Shawkey, M.D., D’Alba, L., Pei, R., Ellison, M., Norell, M.A. and Vinther, J., 2012. Reconstruction of Microraptor and the evolution of iridescent plumage. Science, 335(6073), pp.1215-1219
- “CC462 – Brazilian Teal” by Aaron Maizlish is licensed under CC BY-NC 2.0
- “Four winged thieves” by Durbed is licensed under CC BY-SA 3.0
- Hu, D., Clarke, J.A., Eliason, C.M., Qiu, R., Li, Q., Shawkey, M.D., Zhao, C., D’Alba, L., Jiang, J. and Xu, X., 2018. A bony-crested Jurassic dinosaur with evidence of iridescent plumage highlights complexity in early paravian evolution. Nature Communications, 9(1), pp.1-12
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