Archaeopteryx is an iconic fossil species with feathered wings from the Late Jurassic of Germany. The question of whether this dino-bird was an elaborately feathered ground dweller, a glider, or an active flyer has fascinated paleontologists for many years. European Synchrotron Radiation Facility researcher Dennis Voeten and colleagues have now analyzed new data from three Archaeopteryx specimens and found that the wing bones of the ancient creature were shaped for incidental active flight, but not for the advanced style of flying mastered by modern-day birds.
Was Archaeopteryx capable of flying, and if so, how? Although it is common knowledge that modern-day birds descended from extinct dinosaurs, many questions on their early evolution and the development of avian flight remain unanswered.
Traditional research methods have thus far been unable to answer the question whether Archaeopteryx flew or not.
Using synchrotron microtomography to probe inside Archaeopteryx fossils, Dr. Voeten and co-authors shed new light on this earliest of birds.
Reconstructing extinct behavior poses substantial challenges for paleontologists, especially when it comes to enigmatic animals such as Archaeopteryx. This well-preserved fossil species shows a mosaic anatomy that illustrates the close family relations between extinct raptorial dinosaurs and the birds.
Most modern bird skeletons are highly specialized for powered flight, yet many of their characteristic adaptations in particularly the shoulder are absent in Archaeopteryx specimens.
Although its feathered wings resemble those of modern birds flying overhead every day, the primitive shoulder structure is incompatible with the modern avian wing beat cycle.
“The cross-sectional architecture of limb bones is strongly influenced by evolutionary adaptation towards optimal strength at minimal mass, and functional adaptation to the forces experienced during life,” said Professor Jorge Cubo, from the Sorbonne University, France.
“By statistically comparing the bones of living animals that engage in observable habits with those of cryptic fossils, it is possible to bring new information into an old discussion,” added Dr. Sophie Sanchez, from Uppsala University, Sweden.
Archaeopteryx skeletons are preserved in and on limestone slabs that reveal only part of their morphology. Since these fossils are among the most valuable in the world, invasive probing to reveal obscured or internal structures is therefore highly discouraged.
“Fortunately, today it is no longer necessary to damage precious fossils,” said Dr. Paul Tafforeau, of the European Synchrotron Radiation Facility.
“The exceptional sensitivity of X-ray imaging techniques for investigating large specimens offers harmless microscopic insight into fossil bones and allows virtual 3D reconstructions of extraordinary quality.”
Scanning data unexpectedly revealed that Archaeopteryx’s wing bones, contrary to its shoulder girdle, shared important adaptations with those of modern flying birds.
“We focused on the middle part of the arm bones because we knew those sections contain clear flight-related signals in birds,” said Dr. Emmanuel de Margerie, from CNRS, France.
“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,” Dr. Voeten said.
“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 optimized for enduring flight.”
“We know that the region around Solnhofen in southeastern Germany was a tropical archipelago, and such an environment appears highly suitable for island hopping or escape flight,” said Dr. Martin Röper, from the Bürgermeister-Müller-Museum and the Bayerische Staatssammlung für Paläontologie und Geologie, Germany.
“Archaeopteryx shared the Jurassic skies with primitive pterosaurs that would ultimately evolve into the gigantic pterosaurs of the Cretaceous. We found similar differences in wing bone geometry between primitive and advanced pterosaurs as those between actively flying and soaring birds,” said Dr. Vincent Beyrand, from the European Synchrotron Radiation Facility.
The findings are published in the journal Nature Communications.
Dennis F.A.E. Voeten et al. 2018. Wing bone geometry reveals active flight in Archaeopteryx. Nature Communications 9, article number: 923; doi: 10.1038/s41467-018-03296-8