UNITED KINGDOM

UK-CHINA: Flying dinosaur "missing link" discovered

British and Chinese researchers last week announced the discovery of a missing link in the evolution of flying dinosaurs - an animal that not only bridges the gap between long-tailed and short-tailed flying reptiles but also reinforces a controversial evolutionary theory.

They published details of a new pterosaur in the Proceedings of the Royal Society B: Biological Sciences, which fits exactly in the middle of the gap between two different groups of pterosaurs - primitive long-tailed forms and their descendants, advanced short-tailed pterosaurs some of which reached gigantic size.

The researchers from the University of Leicester and the Geological Institute, Beijing, have christened their discovery Darwinopterus, meaning Darwin's wing. The name honours the 200th anniversary of Charles Darwin's birth and the 150th anniversary of the publication of On the Origin of Species.

More than 20 fossil skeletons of Darwinopterus, some of them complete, were found earlier this year in north-east China in rocks dated at around 160 million years old. The long jaws, rows of sharp-pointed teeth and rather flexible neck of this crow-sized pterosaur suggest that it might have been hawk-like, catching and killing other contemporary flying creatures.

These included various pterosaurs, tiny gliding mammals and small, pigeon-sized, meat-eating dinosaurs that, aided by their feathered arms and legs had recently taken to the air, and would later evolve into birds.

"Darwinopterus came as quite a shock to us," said Dr David Unwin, a member of the research team and based at the University of Leicester's School of Museum Studies.

"We had always expected a gap-filler with typically intermediate features such as a moderately elongate tail - neither long nor short - but the strange thing about Darwinopterus is that it has a head and neck just like that of advanced pterosaurs, while the rest of the skeleton, including a very long tail, is identical to that of primitive forms."

Unwin said the geological age of Darwinopterus and bizarre combination of advanced and primitive features revealed a great deal about the evolution of advanced pterosaurs from their primitive ancestors.

"First, it was quick, with lots of big changes concentrated into a short period of time. Second, whole groups of features (termed modules by the researchers) that form important structures such as the skull, the neck, or the tail, seem to have evolved together. But, as Darwinopterus shows, not all these modules changed at the same time. The head and neck evolved first, followed later by the body, tail, wings and legs.

"It seems that natural selection was acting on and changing entire modules and not, as would normally be expected, just on single features such as the shape of the snout, or the form of a tooth. This supports the controversial idea of a relatively rapid 'modular' form of evolution."

The research team says much more work is needed to substantiate the idea of modular evolution but, if it proves to be true, it might help explain many other cases where rapid large scale evolution must have taken place among animals and plants. The extraordinary evolutionary radiation of mammals following the extinction of dinosaurs is just one example.