How well could "early bird" dinosaurs actually fly?
The dinosaur Archaeopteryx may not be a household name, but its fossils are some of the most interesting and important ever found. With its feathers and light, thin, bird-like bones, the creature is widely regarded as one of the earliest ancestors of modern birds, but the question of whether or not it could actively fly has been debated for decades. Now, scientists have taken X-ray scans of fossil specimens, and concluded that the answer is yes – sort of.
First discovered in 1861, Archaeopteryx captured the imagination of a scientific community just learning about the idea of evolution – Charles Darwin's On the Origin of Species had only been published two years earlier. Looking remarkably like a bird but possessing some distinctly dinosaurian features like teeth and a tail, the strange creature appeared to be a clear transitional fossil.
At a glance, it looks like the creature would have been at home soaring through the Late Jurassic skies, but closer examination revealed that it probably wasn't a strong flier. Studies have found that the animal's shoulder joints are oriented differently to most birds, meaning it probably wouldn't have been able to lift its wings above its back. That's a key component of the flapping method of powered flight seen today, which suggests that Archaeopteryx might have been more of a glider or a short-distance hopper instead.
To help shed new light on the question, an international team of scientists has now conducted synchrotron microtomography scans of several Archaeopteryx fossils. Conducted at the European Synchrotron Radiation Facility (ESRF) in France, this non-invasive technique involves scanning the specimens with X-rays to create a cross-sectional digital 3D model.
"Fortunately, today it is no longer necessary to damage precious fossils," says Dr. Paul Tafforeau, a beamline scientist at the ESRF. "The exceptional sensitivity of X-ray imaging techniques for investigating large specimens that is available at the ESRF offers harmless microscopic insight into fossil bones and allows virtual 3D reconstructions of extraordinary quality."
While much attention had been given to the creature's inefficient shoulder joints, the researchers focused their efforts on the wing bones instead. In birds, some clear flight-related signals can be found there, and the team wanted to check whether Archaeopteryx had these modern adaptations or not.
"We immediately noticed that the bone walls of Archaeopteryx were much thinner than those of earthbound dinosaurs but looked a lot like conventional bird bones," says Dennis Voeten, lead author of the study. "Data analysis furthermore demonstrated that the bones of Archaeopteryx plot closest to those of birds like pheasants that occasionally use active flight to cross barriers or dodge predators, but not to those of gliding and soaring forms such as many birds of prey and some seabirds that are optimised for enduring flight."
Due to its primitive bone structure, the researchers say that Archaeopteryx is probably part of evolution's earliest experiments with active dinosaurian flight. The actual mechanism it used remains unknown, but might be the subject of further study.
"Because Archaeopteryx lacked the pectoral adaptations to fly like modern birds, the way it achieved powered flight must also have been different," says Voeten. "We will need to return to the fossils to answer the question on exactly how this Bavarian icon of evolution used its wings."
In the long run, Archaeopteryx may not have been the most efficient flier, but it would have helped its descendants eventually get off the ground.
The research was published in the journal Nature Communications.