Soft-centred fossils reveal dinosaurs' true colours
27 January 2011 by Jeff Hecht
Magazine issue 2796. [Subscription needed/Requer assinatura]
Newly discovered traces of soft tissue provide unprecedented insights into how animals that died millions of years ago looked and lived
PETE LARSON and Phil Manning mount the dinosaur fossil on a small motorised platform inside the lead-lined chamber. The two palaeontologists make a few final adjustments, then exit the chamber and bolt it tight. At the console, geochemist Roy Wogelius flips a switch, sending a beam of X-rays sweeping over the fossil's surface.
The scene, at the Stanford Synchrotron Radiation Lightsource in California, is reminiscent of Dr Frankenstein animating his monster. And that is essentially what Larson, Manning and Wogelius are trying to do.
Their project is one of several challenges to the conventional wisdom that when animals fossilise, all the original organic material, from the bones to the blood, is lost. Larson, of the Black Hills Institute in South Dakota, and Manning and Wogelius of the University of Manchester, UK, have already detected chemicals in a 145-million-year-old bird fossil that they believe were present in the living creature. Other groups have reported finding proteins and blood vessels inside dinosaur bones, and traces of pigments in 108-million-year-old feathers. The claims are controversial, but if true they promise to breathe new life into our understanding of ancient life.
Source/Fonte: New Scientist
The research could also help locate new deposits of extraordinarily well preserved fossils, says Patrick Orr of University College Dublin in Ireland - sites like the Burgess shale in Canada and Chinese feathered dinosaurs beds that have given us tremendous insights into evolution. Such deposits are usually found by accident, but the more we understand about the conditions that create them the more chance we have of discovering new ones.
First, however, researchers like Manning must convince other palaeontologists that their fossils really do preserve original material, which won't be easy.
Palaeontologists have long studied the process of fossilisation - a field known as taphonomy - by observing the fate of dead animals and measuring what happens to the organic matter. Most of the time soft tissues are completely consumed by predators, scavengers and decay, leaving just scattered and fragmentary bones and teeth. If these fossilise they become mineralised, with all of the original material turned to rock.
Pristine preservation
Occasionally, though, nature is kind and fossilisation preserves details of an animal's soft tissue. For example, the animals of the Burgess shale were buried rapidly in anoxic mud, allowing their soft tissues to be fossilised in amazing detail. Dinosaur "mummies" such as Dakota, a spectacularly well-preserved specimen of the duck-billed dinosaur Edmontosaurus, form when thick-skinned animals are buried quickly in fine river-bed sands, capturing impressions of the skin before the tissue decays. Impressions of feathers from Archaeopteryx were preserved in fine lime deposits on the bottom of a stagnant lagoon, and China's celebrated feathered dinosaurs were fossilised in fine silts and layers of volcanic ash settling to the bottoms of lakes 125 million years ago.
However, even these exceptional conditions were not thought to preserve original organic material. The Chinese fossils are covered in a thin black film of carbon, but this is believed to be remains of bacteria that consumed the soft tissue before being entombed in rock. Convincing evidence of original soft tissue older than the Ice Age was lacking.
That wasn't for lack of trying. The biggest prize was DNA, because it could reveal so much about extinct animals and their relations to living ones.
The 1993 movie Jurassic Park pumped up interest in the search for dinosaur DNA, and a year later Scott Woodward of Brigham Young University in Provo, Utah, claimed to have found dinosaur DNA in 80-million-year-old bone fragments (New Scientist, 26 November 1994, p 12). His report in Science (vol 266, p 1229) made headlines across the world, but the DNA was soon found to be contamination from humans who had handled the fossil.
Technology has advanced tremendously since then. DNA has now been extracted and sequenced from mammoths, the bones of Neanderthals, and extinct cave bears. But recovering DNA from dinosaurs remains the stuff of fiction. DNA degrades much faster than proteins and other soft tissue components and nobody thinks it is possible to recover DNA that is older than about a million years.
But DNA is not the only game in town. The controversy surrounding the supposed dinosaur DNA made a lasting impression on Mary Schweitzer, who was then a graduate student at Montana State University in Bozeman. Ten years later, she reported recovering soft, flexible tissues from inside the leg bone of a 68-million-year-old Tyrannosaurus rex which she claimed were blood vessels (Science, vol 307, p 1952).
The T. rex was discovered in a remote South Dakota canyon in 2000 by a team from the Museum of the Rockies. Its femur was intact but too heavy for a helicopter to lift in one piece, so they had to break it. To everyone's surprise the interior was hollow - fossilised bones are usually filled with minerals - so the excavation team took samples and sent them to Schweitzer for analysis. She soaked the samples in a solution to dissolve the calcium compounds in the fossil, and was surprised to be left with flexible tissue which she identified as blood vessels.
Schweitzer's claim was met with scepticism, in part because of the immense age of the bone. "The cynics think it's far too old," says Derek Briggs of Yale University. Tom Kaye of the University of Washington in Seattle suggested that what she had found was a biofilm left by bacteria that had feasted on the dead animal (PLoS One, vol 3, p e2808).
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PERGUNTA INDISCRETA DESTE BLOGGER:
Tecidos moles em fóssil de Archaeopteryx? 120 milhões de anos atrás??? E os outros casos de tecidos moles? Até Tiranossauro rex??? Onde que esta onda de tecidos moles em fósseis de animais de eras antigas vai parar? Ué, mas isso é possível? Como? Alguém me belisque...
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PERGUNTA INDISCRETA DESTE BLOGGER:
Tecidos moles em fóssil de Archaeopteryx? 120 milhões de anos atrás??? E os outros casos de tecidos moles? Até Tiranossauro rex??? Onde que esta onda de tecidos moles em fósseis de animais de eras antigas vai parar? Ué, mas isso é possível? Como? Alguém me belisque...
