The feather link
researchers are convinced that birds are the descendants of dinosaurs. This theory gets credence from the recent discovery of fossil that has clear traces of feathers from head to tail. The fossil also supports the theory that some dinosaurs developed feathers not to fly but to keep themselves warm.
The New York-based American Museum of Natural History unveiled the fossil, which is on loan from the National Geological Museum of China. The fossil, embedded in two slabs of fine-grained rock, is estimated to be around 130 million years old. It was unearthed by farmers in Liaoning province in northeastern China last year. The fossil resembles a duck with a reptilian tail. Its head and tail are edged with the imprint of downy fibres. The rest of the body, except for bare lower legs, shows distinct traces of tufts and filaments that appear to have been primitive feathers. On the backs of its short forelimbs are patterns of what looks like modern bird feathers.
Several species of dinosaur with feather-like structures have been found in Liaoning's fossil beds since 1995. But in most cases, the fossils have been jumbled or incomplete, making it difficult to prove how the feather-like structures were part of the dinosaur's body. The new fossil is important because it offers far more complete and compelling evidence of feathered dinosaurs than most of the other similar specimens that have been excavated in recent years, claims James Clark, an associate professor of biology at George Washington University, usa .
A team of us and Chinese scientists say that the recently discovered fossilised creature belongs to a group of small, fleet-footed dinosaurs known as dromaeosaurs, which are the most closely related dinosaurs to modern day birds. Dromaeosaurs are a subgroup of dinosaurs known as theropods. Mark Norell, chairperson of the division of paleontology at the American Museum of Natural History, says that the paleontologists based their conclusion on the presence of several anatomical features that are unique to dromaeosaurs, including a hyper-extendable curved claw on the middle toe and stiffening rods in the tail. Because birds and some dinosaurs, particularly theropods, have so many anatomical features in common, many paleontologists have concluded that birds evolved from dinosaurs. The presence of feathers does not necessarily mean that dinosaurs could fly. Some non-avian dinosaurs, especially smaller species, may have acquired a fur to help maintain their body temperature, claim the paleontologists.
Norell said that the new fossil and similar evidence of feathered dinosaurs acquired in the past decades is radically altering common ideas about the nature of dinosaurs such as therpods.
The forelimbs of the Chinese fossil are too short to have supported wings and so it was flightless, asserts Norell. Modern birds are warm-blooded and their feathers play an integral role in keeping them warm, therefore, non-avian dinosaurs developed primitive feathers at the time they developed warm-bloodedness, said Norell. Hans-Dieter Sues, a dinosaur paleontologist at the Royal Ontario Museum in Toronto, Canada, said the discoveries from Liaoning "further strengthen the case for the theropod-bird connection and also establish that feathers originated and eventually diversified in nonflying nonavian theropod dinosaurs. Norell said the feathered fossil showed that there was a more general distribution of feathers than in birds alone.
But this connection between birds and dinosaurs has been questioned by ornithologists. They argue that birds evolved from reptiles. They say that the marks that were being interpreted as feathers in the fossil could be impressions from the dinosaur's skin. The theropod origin of birds has been oversold on the basis of wishful thinking and that fossil evidence suggesting that some dinosaurs had feathers is too sketchy to support these claims. Any feathers that have been documented could have come from birds that nested amid theropods, says Storrs Olson, curator of birds at the Smithsonian Institution's Natural History Museum, usa .
If the claim of the paleontologists proves to be correct, then studying theropods that lived earlier than the first birds can provide an insight into bird evolution. The Liaoning province in northeastern China has yielded fossils that are in a good condition because the animal remains were buried under fine sediment of volcanic ash and muck.