By Ashley Strickland, CNN
Updated: Tue, 13 Mar 2018 18:48:09 GMT
For more than 150 years, researchers have been studying the fossils of bird-like dinosaur Archaeopteryx and attempting to answer this question: Did it fly?
Although it may sound simple, the fossils of the feathery-winged dinosaur, found largely in Germany, don't give up their secrets so easily. The bones are preserved in limestone slabs, and attempting to remove them for greater analysis would damage them. These fossils are some of the most valuable in the world, according to researchers.
But X-ray imaging techniques available at the European Synchrotron Radiation Facility in Grenoble, France, allow for visualizing obscured properties of fossils without causing damage. This gave researchers the opportunity to take a closer look at Archaeopteryx. Their findings are detailed in a new study in the journal Nature Communications on Tuesday.
Scientists know that birds evolved from dinosaurs, and Archaeopteryx is part of that evolutionary path. Archaeopteryx preceded the oldest bird by 75 million years. And as we know from looking at modern birds like penguins and ostriches, just because they have wings doesn't mean they can fly. The same could be said of Archaeopteryx, which has caused questions as to whether it was a flightless land-dweller, a glider or a flier.
Because its fossils are well-studied, researchers knew that if Archaeopteryx could fly, it wasn't comparable to how birds do, because it had a primitive shoulder structure that wouldn't support the downward power and upward recovery wing strokes that modern birds use.
Of course, flight motion itself does not fossilize, and the flight pattern of Archaeopteryx cannot be studied in a living animal anymore, which makes determining flight style even more difficult, lead study author Dennis Voeten wrote in an email. Voeten works with the European Synchrotron Radiation Facility and is a PhD candidate at Palacký University in the Czech Republic.
But the X-rays revealed new finds within the arm bones of Archaeopteryx.
"It was surprising to see that the wing bone geometry of Archaeopteryx looks remarkably more like those of modern birds than expected. The variation within modern flying birds is much larger than the differences between Archaeopteryx and the short-flying birds in our data set," Voeten said. "Although the anatomy of Archaeopteryx was incapable of executing the flight stroke of modern birds, this similarity accounts for the strongest evidence for active flight in this animal presented in 150 years of research."
The bones themselves were hollow, a trait exclusively shared with flying birds and pterosaurs, which suggested that Archaeopteryx could fly.
Statistical comparison placed the bones of Archaeopteryx very close to those of mostly ground-dwelling birds such as pheasants and roadrunners, Voeten said. This supported the idea of active flight for Archaeopteryx, meaning it could fly to escape predators or over short distances to reach new locations, as pheasants and roadrunners do.
About 150 million years ago during the Jurassic period, when Archaeopteryx lived, the southeastern part of Germany where the fossils were found would've been a tropical archipelago. So they could have flown from island to island.
Voeten and his colleagues also noticed that the bones were well-developed for blood vessels, which could suggest active flight, but they believe that more research is needed regarding this point.
So what would active flight look like, if it's not the up and down flapping of modern birds? Archaeopteryx was probably incapable of raising its wings over its back, Voeten said, because of its primitive shoulder structure and lack of a strongly keeled breastbone attached to the flight muscles.
The study does not attempt to definitively describe the flight style, but Voeten and his team believe that because of the shoulder girdle, it's possible that Archaeopteryx had a flight stroke that oriented forward and up, followed by a power stroke oriented rearward and down -- almost like the butterfly stroke. Future research is needed to refine their hypothesis.
There's a reason why this type of flight is not observable in birds today: It went extinct because it wasn't effective.
"Archaeopteryx is not a direct ancestor to modern birds but rather a member of a larger group of elaborately feathered dinosaurs that appears to have engaged in a variety of experimental modes of dinosaurian flight," Voeten said. "Today, 150 million years later, all styles of dinosaurian volancy (flying) except the flight modes of modern birds have gone extinct. We feel our study supports that the evolution of dinosaurian flight was not simply a straight line towards the flight of modern birds but involved an exotic diversity of alternative, experimental and intermediate solutions that ultimately proved to be evolutionary dead-ends."
During the Jurassic period over the German archipelago, the only company Archaeopteryx would've had in the skies were primitive pterosaurs. But this study shows that by the late Jurassic, dinosaurian flight had already evolved.
"This implies that the search for the first free flying dinosaurs, which will add to our understanding of the very origin of dinosaurian flight, should focus on fossils older than Archaeopteryx," Voeten said.
Voeten and his colleagues want to answer new questions raised by this latest research, especially refining how Archaeopteryx flew, as well as other aspects of its lifestyle and physiology.
"Untangling the competing evolutionary forces that acted on now-fossilized bones towards bringing long-extinct animals back to life, so to speak, is a very rewarding occupation, especially when it considers the beautifully preserved fossils of the still-enigmatic Archaeopteryx," Voeten said. "From a historical perspective, it is clear that Archaeopteryx represents a true icon of evolution: It played an important role in both the early communication of Darwin's theory of biological evolution and, later, in the recognition that birds are, in fact, dinosaurs.
"With 11 specimens of Archaeopteryx presently known, which makes Archaeopteryx a comparatively well-sampled dinosaur, it is quite remarkable that this taxon remains somewhat mysterious to this very day. Having been able to contribute to our knowledge on this animal has been a very satisfying experience."