The secrets of Darwin's dinobird

The Archaeopteryx “Thermopolis specimen” is considered one of the most highly preserved examples of a transitional species linking dinosaurs and birds.

A keystone of evolutionary history, the Thermopolis Archaeopteryx fossil, visited SLAC National Accelerator Laboratory in December 2008 to undergo a revolutionary type of analysis. Using intense X-ray beams, scientists searched for characteristics of the "dinobird" that have eluded all previous scientific analyses.

Researchers at SLAC's Stanford Synchrotron Radiation Lightsource (SSRL) are attempting to uncover secrets of the Archaeopteryx hidden from view since the creature sank to the bottom of a shallow lagoon and became entombed in limestone some 150 million years ago. Only ten Archaeopteryx fossils have been found and studied. These specimens have undergone extensive visual analyses and even CT scans in the past, but never anything as comprehensive as the X-ray imaging researchers utilized at SSRL. Here, researchers made the first maps of the chemical elements hidden within one of the best preserved specimens, possibly including remnants of soft tissue—not just bone.

Paleontologist Peter Larson seals the Archaeopteryx fossil in preparation for X-ray imaging studies in a chamber that will be filled with helium.

Archaeopteryx holds a unique place in history. A century and a half ago, just a year after Charles Darwin published On the Origin of Species, the discovery of this fossilized half-dinosaur/half-bird species provided the strongest evidence yet for the theory of evolution. Approximately 16 by 16 inches in size, the Thermopolis specimen was originally discovered near Solnhofen, Germany, and is now owned by the Wyoming Dinosaur Center.

By tuning SSRL's hair-thin X-ray beam to specific energies and sweeping it across the fossil, researchers have revealed detailed maps of the chemical remains, which are currently being analyzed. This technique, called X-ray fluorescence imaging, is more commonly applied to very small samples, but has recently been used on historical documents including the Archimedes Palimpsest and a van Gogh painting.

In addition to offering an entirely new view on a long-extinct animal, this work may also reveal more about fossilization itself. By understanding how fossilization occurs and what exactly is preserved in the process, researchers will be able to deduce much more about ancient organisms and evolution.