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In December 2008, researchers at the SLAC National Accelerator Laboratory used the Stanford Synchrotron Radiation Lightsource (SSRL) to shine intense X-ray beams on the so-called "dinobird" to reveal secrets that have been hidden from view for millions of years. The prehistoric bird that goes by the half familiar name of Thermopolis archaeopteryx is probably one of the most well-known fossils after Tyrannosaurus rex. It represents a keystone in evolutionary theory bridging the gap between land-locked creatures and those with wings that can take to the air. However, for decades archaeologists have been limited in their studies to what can be seen with naked eye when investigating fossils. Now, the SLAC team is revealing what lies beneath the surface of this critical evolutionary fossil known as Darwin's dinobird. 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 fossilized remains of this half-dinosaur/half-bird creature just half a metre in height, offered the first strong physical evidence for Darwin's theory of evolution. The first specimen was discovered near Solnhofen, in Germany, and is known in German as Urvogel, meaning original bird. Its scientific name is derived from the Greek, archaios meaning 'ancient' and pteryx meaning wing. The specimen examined at SLAC, which is one of ten known, is owned bv the Wyoming Dinosaur Center. The WDC specimen was fossilised after the animal sank to the bottom of a shallow lagoon and was entombed in limestone some 150 million years ago. The various specimens have undergone extensive visual analyses and even computerised tomography (CT) scans in the past. However, this is the first time they have been subjected to a comprehensive analysis using the X-ray fluorescence imaging facilities available at the SSRL. The same technique has been used previously and in a non-invasive to analyse historical documents including a van Gogh painting and the Archimedes Palimpsest, the latter of which SSRL staff scientist Uwe Bergmann worked previously. With this technology, the researchers have made the first maps of the chemical elements hidden within one of the best preserved specimens, possibly including remnants of soft tissue. According to Bergmann, the chemical elements, silicon, calcium, potassium, and iron, can be preserved during fossilisation although the soft tissues from which they were originally derived may not be visible to the naked eye. The unique characteristics of each element becomes visible to high intensity X-rays, however, and reveal the position of particular tissues, calcium for bone, perhaps. He says, that by determining the distribution of various chemicals within the fossil it might be possible to recreate anatomical details. The results of the study will not only reveal much about Archaeopteryx, but could also provide scientists with new insights into the fossilisation process 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. While archaeopteryx provides a missing link between dinosaurs and birds, earlier this year the discovery of a flightless, yet feathered fossil from the Middle to Late Jurassic of China, complicated the picture somewhat. The pigeon-sized creature lived a little before Archaeopteryx although is still very much bird-like in many ways, including the presence of four very long ribbon-like tail feathers and a short tail. Fucheng Zhang of the Chinese Academy of Sciences, Beijing, China and colleagues described in the journal Nature how this species shows no sign of flight feathers as seen in other bird-like dinosaurs such as Microraptor. This new fossil adds yet more complexity to the early history of evolution from dinosaurs to birds. Related links:
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