Insights on flight origins and how winged dinosaurs lived

21 December 2022

Palaeontologists have analysed the shapes and patterns of foot structures in exceptionally preserved fossils to find clues on the ecological transitions and lifestyles of early theropod flyers from the Late Jurassic and Early Cretaceous.

Near-complete, semi-articulated right pes of Microraptor fossil: a) under a white light, b) laser-stimulated fluorescence, and c) close-up of reticulate and scutellate scales on digit IV, and d) interpretive drawing. Credit: Nature Communications

In living birds, foot shape varies greatly relative to function, function, and diet. The shape and pattern of the toe pads and foot scales, hinging of foot joints, and claw shape and size all inform the grasping ability, running proficiency and feeding style. An international research team assessed more than 1,000 fossils from northeast China of early birds and their close flying relatives. They used the laser-stimulated fluorescence technique to find a handful of specimens in which the soft tissue had been particularly well preserved.

“The feet of living birds tell us a lot about their lifestyles," Dr Michael Pittman, assistant professor at the Chinese University of Hong Kong and lead author of the study, said. "On this basis, we were able to refine what we know about the lifestyles of early birds and their closest flying relatives, and how this changed through time.”

The first flying birds like Anchiornis and Archaeopteryx from the Jurassic period show adaptations that suggest ground-dwelling lifestyles. Birds then diversified into aerial lifestyles in the Early Cretaceous, tendencies shown by generalists such as the Confuciusornis and specialists like the climbing Fortunguavis. Some early birds like the Early Cretaceous Sapeornis show complex lifestyles that seem to be unique compared with living birds.

Pedal morphology of select early theropod flyers: schematic of select early theropod flyers showing the proportions and arrangement of the toe bones and the morphology and arrangement of the toe pads. Credit: Nature Communications

One surprise in the study involved Microraptors, four-winged dromaeosaurid dinosaurs from the Early Cretaceous. The researchers found that this close flying-relative of birds likely had a specialised, raptorial lifestyle. Their hawk-like characteristics had been rare amongst known early flyers, suggesting that some early non-bird flyers performed specialised roles that are filled by birds such as hawks today.

“Our [laser-stimulated fluorescence] data allowed us to see soft tissues preserved around the feet that we didn’t know were there," said Thomas G Kaye from the US-based Foundation for Scientific Advancement. He is a co-author of the study and pioneer of the technique. "Our work nicely illustrates how palaeontology is advancing through new imaging techniques.”

The findings were published in Nature Communications.