Researchers report today in Science Express that they have taken a big step in determining what the first birds looked like more than 100 million years ago, when their relatives, the dinosaurs, still ruled the Earth. At the Department of Energy’s SLAC National Accelerator Laboratory, they discovered chemical traces of a pigment, an important component of color, that once formed patterns in the feathers of the fossilized birds. Pictured here is a synchrotron rapid scanning x-ray fluorescence image of the calcium distribution in a fossil specimen of Confuciusornis sanctus, an ~120 million year old avian species, the oldest documented to display a fully derived beak. Calcium is high in the bones as shown by the bright white areas, but calcium is also high in the areas corresponding to residue of downy feathers in the neck region. This is interpreted to be due to the distribution of calcium being controlled by eumelanin chelates in the neck feathers, indicating that these soft tissues were originally darkly pigmented. Credit: Data were collected at SLAC’s Stanford Synchrotron Radiation Lightsource, image created by Gregory Stewart (SLAC). |
Scientists
report today that they have taken a big step in determining what the
first birds looked like more than 100 million years ago, when their
relatives, the dinosaurs, still ruled the Earth. At the Department of
Energy’s SLAC National Accelerator Laboratory, they discovered chemical
traces of a pigment, an important component of color, that once formed
patterns in the feathers of the fossilized birds.
The
pigment, eumelanin, is one of the coloring agents responsible for brown
eyes and dark hair in many modern species, including humans. It would
have been one of the factors that determined the birds’ color patterns,
along with structural properties of the birds’ feathers and other
pigments they ingested as part of their diets.
The discovery, reported June 30 in Science
Express, will help give textbook illustrators, diorama makers and
Hollywood special-effects artists a more realistic palette for their
depictions of ancient animals. Understanding these pigment patterns is
important for science, too, since they play a role in a wide range of
behaviors that are important in evolution such as camouflage,
communication and selecting mates.
“This
is a pigment that evolved a very, very long time ago but is still
actively synthesized by organisms on the planet, and we found a way to
map it and show its presence over 120 million years of geological time
passing,” said geochemist Roy Wogelius of the University of Manchester,
one of the leaders of an international team that reported the discovery.
“It is a direct relationship between you, me, and some extremely old
organisms.”
Said
report co-author Uwe Bergmann of SLAC, “If we could eventually give
colors to long extinct species, that in itself would be fantastic.
Synchrotron radiation has revolutionized science in many fields, most
notably in molecular biology. It is very exciting to see that it is now
starting to have an impact in paleontology, in a way that may have
important implications in many other disciplines.”
Working at SLAC’s Stanford Synchrotron Radiation Lightsource, the researchers examined two fossilized birds. Confuciusornis sanctus,
which lived 120 million years ago, was one of many evolutionary links
between dinosaurs and birds, sporting the first known bird-like beak. Gansus yumenensis, considered the oldest modern bird, lived more than 100 million years ago and looked a bit like a modern grebe.
Scientists
had previously found melanosomes—the biological “paint pots” where
melanin pigments are made and stored—in both ancient and living
organisms. They used information about the structures of the melanosomes
to make an educated guess about the colors of the pigments inside. But
the newly published research shows that this prior approach has
limitations. The team looked instead for chemical traces of the pigments
themselves with two sophisticated X-ray techniques developed at SSRL.
The
first technique identifies specific chemicals or elements in a sample,
and it can examine whole fossils rather than the tiny fragments used in
previous methods, revealing pigment patterns across the whole specimen.
With it, the researchers unveiled traces of specific elements in and
around the tissues, bones and surrounding rock of Confuciusornis sanctus. These traces provide an image of the pigmentation patterns from this long-dead bird in eerie detail.
The
most striking of these trace elements was copper. As Bergmann points
out, copper, which can be toxic in high levels, has persisted in the
fossil in significant amounts, appearing in the images as a ghostly glow
in places where feathers remained. What was it doing there? Before they
could answer that, the researchers had to determine what chemical form
the copper took.
SSRL
staff scientist Sam Webb used the second X-ray imaging technique to
study the fossil of a single feather from Gansus yumenensis. His
analysis revealed that the copper in the fossil took the same form as
copper trapped by eumelanin pigment. What’s more, Webb said, “When we
looked outside the feather we didn’t see the copper at all.”
Couple
that chemistry with the way the copper was distributed, and the
research team was faced with a mind-boggling conclusion: They had seen
actual color patterns in the fossil bird feathers. “There is a
stunningly remarkable preservation of pigments,” Wogelius said. The team
found the same relationship between copper and pigments in samples from
modern feathers and squid.
“These
new techniques for teasing out evidence of pigmentation will take a lot
of the guesswork out of reconstructing the appearance of extinct
dinosaurs and birds,” said renowned dinosaur illustrator James Gurney,
author of the best-selling Dinotopia series.
The
discovery opens a window on the biochemistry of ancient creatures, and
could lead to a far greater understanding of what they ate and the
chemistry of their surroundings.
“The
fossils we excavate have vast potential to unlock many secrets about
the original organism’s life, death and subsequent events impacting its
preservation,” said paper co-author Phil Manning, a paleontologist at
the University of Manchester. “In doing this, we unlock much more than
just paleontological information. We now have a chemical roadmap to
track similar pigments in all life.”
