Archaeopteryx is one of the most famous fossils ever found, a crow-size creature with big legs, a bony tail, a mouthful of teeth -- and feathers. Discovered only two years after publication of Charles Darwin's "Origin of Species," it became an instant sensation as the epitome of evolution -- a bird, yes, but only just.
For decades, scientists studied the aerodynamics of archaeopteryx to determine whether it could fly. The consensus was that it probably could, but not well: "It is an unusual animal," said paleontologist Angela Milner of London's Natural History Museum. "It's like a dinosaur skeleton with feathers."
But in a study released today, a multinational team of experts that included Milner presented new evidence that bolstered the case that the creature was a capable flier. Archaeopteryx's tiny brain -- about the size of a little-finger joint -- has much more in common with those of modern birds than it does with those of the reptiles that were its forebears.
Using modern X-ray scanning techniques to examine the inside of the fossil skull, Milner and her colleagues found that archaeopteryx's brain emphasized vision and a highly developed spatial sense and had the tools to coordinate these attributes in a sophisticated way.
"These are the parts of the brain concerned with flight control," Milner said. "The brain of archaeopteryx does not look like a living reptile at all." The team reports the new findings in today's issue of the journal Nature.
The research, however, does little to illuminate how archaeopteryx, 147 million years old, relates to more recently discovered -- and much more recent -- feathered dinosaurs regarded by many paleontologists as the precursors of modern birds.
"The assumption for a long time has been that we would and should find evidence of these advanced predatory [feathered] dinosaurs at least as old as archaeopteryx," said Ohio University evolutionary biologist Lawrence Witmer, who wrote a commentary accompanying the new findings. "After all, you can't be older than your grandparents."
There are seven known examples of archaeopteryx, all of them excavated from a German limestone quarry. The "London specimen," used in Milner's study, was the first one found, in 1861, and was sold to the British Museum in 1862.
"Archaeopteryx is the textbook example of the missing link," Witmer said. "It is important beyond its value as a biological specimen. It's truly an icon, and when you're in the presence of it, you feel different."
But archaeopteryx was difficult to characterize. Wings and feathers marked it as a bird, but it had a full set of teeth, as a reptile has, as well as strong, heavy reptile legs and claws on its wings. Its bony tail was good for balance, as a reptile's is, but the tail had feathers, perhaps to help as an airfoil.
"Did it live in trees or on the ground? The debate's been going for decades," Witmer said. "We have no data. Archaeopteryx is about the size of crow, so it's not too big to climb, but it also had nice back legs for running on the ground. It's hard to decide what the major mode was. It was a generalist."
Until the advent of modern X-ray techniques, Milner noted, it was impossible to assess archaeopteryx's sensory abilities without cutting into the skull -- unthinkable for such a priceless artifact. But the new study opened a non-destructive window into its brain.
"Our research is in line with the idea that archaeopteryx was capable of at least limited flapping flight, rather than just gliding," Milner said. "It didn't have a big breastbone, so it had less power."