September–October 2014 77Her research indicated that melanosomes shrink during fos-
silisation, which might aff ect their shape and therefore the
reconstructions of their colour. Jakob’s response was that
the melanosomes shrank almost equally in several dimensions,
so his reconstructions of colour shouldn’t be aff ected. Only
time and more research will tell whether or not the fantastic
new visions of coloured dinosaurs are accurate.B
IRDS, INSECTS AND FISH, however, have another trick
besides pigment up their sleeves, and it allows them to
be decorated in a much brighter, brasher range of gaudy
hues than we comparatively drab mammals could ever hope for.
Iridescence is so-called structural colour, which occurs when
light bounces off physical features in the surface of feathers or
scales and is split into diff erent colours, in much the same way a
prism splits white light into its constituent colours. Some birds- parrots with green plumage, for example – use a mixture of
both yellow pigments and blue iridescence to create their colour.
The structural features that manipulate the light vary, but
include wafer-thin stacks of translucent organic material that
interferes with and refl ects light. These fi lms, made of chitin
in insects, can refl ect and amplify light of one particular colour
or wavelength over and above others. This is how iridescent or
metallic hues are produced, such as those that adorn the feathers
of birds of paradise and peacocks, the wings of butterfl ies and a
whole spectrum of beetles. Sir Isaac Newton, who shed much
light on optics and refraction, was the fi rst to reveal that minute
layered structures were the cause of colour in peacock feathers.
In 2003 I fi rst learnt about the possibility of structural colours
persisting in fossils when I wrote a story about a 50-million-
year-old beetle fossil that still had a brilliant blue iridescent
sheen – in this case, the fossil was so incredibly well preserved
that the ‘multilayer refl ector’ that created the colour in the sur-
face of its exoskeleton was still intact. At the time, the fossil was
the oldest known to retain any bright colour and it may still hold
that record. Australian palaeontologist Professor Andrew Parker
said then that we might one day be able to study the physical
features of dinosaur fossils to predict what colours their feathers
might have been. It seemed like science fi ction to me, so it was
a thrill to see the idea come to fruition just seven years later.
Jakob, Mike and their co-workers at Bristol University
have been able to fi nd evidence of these structural iridescent
colours in fossilised dinosaur feathers by looking at the density,
orientation and stacking of the melanosomes. In some cases,
melanosomes act to produce colour in two ways: through
Birds, insects and fish
have another trick besides
pigment up their sleeves.
RYAN MACKELLAR / SCIENCE / UNIVERSITY OF ALBERTAag0914_JohnsdinosP77 - 73 2014-08-11T16:16:25+10:00