Analysis: remarkable new evidence has found that flying reptiles could change and control the colour of their feathers
Pterosaurs are flying reptiles with long leathery wings and are some of the most evocative fossils. Powerful flyers but ungainly and awkward on land, they appeal to our sense of mystery but also inspire mild bemusement, especially forms that appear top-heavy because of their large exaggerated headcrests. A common misconception is that pterosaurs are dinosaurs, but they are in fact a separate branch on the reptile family tree.
The scientific study of pterosaur biology has always been contentious. They are thought to have had various unique body features not found in dinosaurs, but this is not universally agreed. An especially controversial aspect of pterosaur biology is the nature of their body covering. Palaeontologists have known for many years that pterosaurs had a fuzzy outer coat, but assumed that it was made of features called pycnofibres, thought unique to those animals.
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From RTÉ Radio 1's Drivetime in 2019, Prof Maria McNamara from UCC on her research into dinosaurs, birds, feathers and flying reptiles
In 2019, the boat was rocked by our discovery that pycnofibres are, in fact, feathers when we found branched feathers in two juvenile pterosaurs from China. Not everyone agreed, partly because the style of feather branching is different to modern-day birds. The feathers have tufts of branches at the base, tip, or mid-way along the shaft (like some dinosaurs). Some scientists argued that the fossil branched structures could be the decayed remnants of other body features.
Now, we have discovered branched feathers in a new pterosaur specimen from Brazil, and the style of branching is more bird-like. In these specimens, there are closely spaced branches all along the length of the feather shaft. This puts to rest any doubts that pterosaurs had feathers - and supports our earlier claims that feathers must have evolved in the common ancestor of pterosaurs and dinosaurs.
Where things got really exciting is when we studied the pterosaur feathers with powerful electron microscopes. We discovered preserved melanin granules – melanosomes – in the feathers. This in itself is not new – melanosomes are fossilised in many different fossil species – but what was completely unexpected was that the melanosomes had different shapes in the different feather types.
In modern day birds, and in many dinosaurs, feather melanosomes have different shapes. The different melanosome shapes are linked to different colours: ball-shaped melanosomes and reddish-ginger colours, sausage-shaped melanosomes to black and dark browns, and stubby rods to greys and other colours. Melanosomes with different shapes have different proportions of melanin pigments inside. Since these pigments absorb light of different wavelengths, they produce different colours. Birds use this ability to produce different colours and colour patterns for camouflage, mating displays and to advertise fitness.
The fact that we found the same feature – melanosomes of different shapes in different feathers – in pterosaurs is strong evidence that this too was a common feature between the two groups of animals. It probably originated in the common ancestor of birds (and other dinosaurs) and pterosaurs, back in the Early Triassic, 200 million years ago.
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From UCC, Prof Maria McNamara on the new evidence that the flying relatives of dinosaurs were able to control the colour of their feathers using melanin pigments
The complex network of genes that is responsible for tuning melanosome shape was therefore probably present in those Early Triassic reptiles, telling us that colour – and colourful visual signals – were a feature of early feathers. Therefore the driving force behind the early evolution of feathers was not just the need to keep warm, but the need to be coloured and have colour patterns.
Going forwards, the palaeontological community should turn its gaze to other pterosaurs to examine their feathers in more detail. Any preserved colour patterns could give us further insights into pterosaur coloration and communication. This would allow us to compare the types of visual signals in pterosaurs with those in birds and other dinosaurs, expanding our understanding of the behaviour of these ancient animals and helping to bring the past to life.
The views expressed here are those of the author and do not represent or reflect the views of RTÉ
