Feathers

In October 1996, Michael Benton was in New York City attending the annual meeting of the Society of Vertebrate Palaeontology at the American Museum of Natural History. The atmosphere was electric. He recalled hurried encounters in hallways featuring black and white photographs and stunned reactions. Yale University’s John Ostrom – the leading expert on fossil birds and dinosaurs at the time – said the images left him “in a state of shock”. Another dinosaur expert, Phil Currie, then at the Royal Tyrrell Museum of Palaeontology in Drumheller, Canada, described being “bowled over”.

At the centre of all the fuss was a specimen that had recently been uncovered in China. No paper had yet been published describing the animal, but Pei-ji Chen at the Nanjing Palaeontology Institute had pictures, and they were jaw dropping. They showed a feathered dinosaur – the first ever seen in the West. It confirmed what Ostrom, Currie and others had long been arguing: birds are dinosaurs. As Malcolm Browne wrote in The New York Times: “Rarely are scientific findings of this possible importance presented so casually.”

Since then, excavations in China have unearthed some 55 species each of dinosaurs and birds, including more than 30 dinosaur species with feathers. For example, even though fossils show that Tyrannosaurus rex had scaly skin, tyrannosauroids unearthed in China had rich feather coverings, so Benton argues that we assume that all members of the group had feathers, at least as juveniles.

However, what is a feather? This is one of the biggest challenges when it comes to determining whether or not a dinosaur had feathers. Over the millions of years of evolution the skin of animals have developed in different ways such as armour plating (crocodiles) or fur (mammals). Feathers are just another example of what animals have done with the structure of skin and to be a proper feather, there are characteristics that need to be fulfilled. The structures must be made from a protein called beta-keratin, they must be branched, and finally they must originate from a follicle.

Tupandactylus imperator

But why would dinosaurs develop feathers at all? Maria McNamara at University College Cork in Ireland and her colleagues found preserved feathers on a fossilised partial pterosaur skull excavated in Brazil. Specimens of this particular species, Tupandactylus imperator, have prominent crests on their heads; the feathers on this skull were found on either side of the crest.

The researchers found two types of feathers: whisker-like monofilaments and more complex branching feathers. When examined under a microscope, each type of feather contained different sorts of melanosomes, tiny pieces of cells that synthesise and store the pigment melanin.

“The specific colours don’t really matter from an evolutionary sense; what matters is that they have these different colours,” says McNamara. “It probably means that the ability to impart colour is something that’s really ancient and that’s tied up in the whole way that feathers were evolved.” Because both pterosaurs and some dinosaurs had multicoloured feathers, the feathers were probably passed down from a common ancestor in the early Triassic period, around 250 million years ago, she says.

These illustrations of an Ornithomimus and an Ostrich show the link between past and present:

Michael Benton states that if the feathers were all the same colour, they might have been used only for insulation, but the finding of multiple colours indicates that they were probably used for signaling as well, perhaps for camouflage or attracting mates.

While I was finding all this out I started to wonder whether it would make me feel safer being chased by a scaly or a fluffy colourful dinosaur. I haven’t decided yet.

The Coloration of Feathers

For glory and brilliance the colours of feathers
are unsurpassed. Yet the pigments which produce
those shades are few. Some (called subjective
or optical colours) are illusions formed
by the quills' pattern and its achromatic,
horny surface. Is other creatures' vision
of them different, paler or darker than ours?

Melanin, from blood-plasma or haemoglobin,
makes black, brown and grey; turacin, which fades
when wet, will flush to purple. Darwin wrote
that natives of the Amazonian region
feed fatty fish to green parrots so the lipochromes
will streak them red and yellow (the sacred
tints of royal Inca's feather garments).

Prismatic and metallic tones: blue, gold
and glossy black, are the structural colours.
Only the white lacks underlying pigment.
The evolution of vivid plumage began with
the struggle to win a mate. But the drab hues
of survivors disturb: such complex beauty
unnecessary after that triumph.

                                             Ruth Fainlight (1931 - )

Thanks for reading,
Terry Q