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An international research team led by The Chinese University of Hong Kong (CUHK)’s School of Life Sciences has uncovered that early multi-winged dinosaurs were already capable of utilising sophisticated aerodynamic features found in modern birds and insects while gliding. The study focuses on Microraptor, a bird-like dinosaur from the Cretaceous period (about 143 to 66 million years ago). The research uses quantitative computer simulations for the first time to analyse how airflow interacted with Microraptor’s forewings and hindwings during gliding. The findings have been published in the prestigious scientific journal Proceedings of the National Academy of Sciences of the United States of America (PNAS).

The secrets behind Microraptor’s flight

Microraptor possessed feathers on both its arms and legs, forming a unique four-winged body plan. For decades, palaeobiologists have debated how this strange body plan was used. To address this, Professor Michael Pittman, Assistant Professor at CUHK’s School of Life Sciences, with his Postdoctoral Research Fellow Dr Csaba Hefler, combined anatomical fossil data with state-of-the-art computational aerodynamics and analysis. They discovered that the generation of lift in Microraptor was aided by vortices[1] bound to the leading edge and tips of its wings, together with forewing to hindwing downwash flows[2] and other inter-wing aerodynamic interactions that enhanced gliding performance.

Professor Pittman said: “This is to our knowledge the first study to use quantitative computer simulations to understand advantageous forewing-hindwing interactions in a multi-winged vertebrate flyer. We conducted first-principle Navier-Stokes equations-based investigations[3] to compute airflow and the generated aerodynamic forces over our Microraptor model to estimate flight benefits in this multi-winged configuration. The results show that Microraptor was a proficient glider that used its wings synergistically to boost lift generation. Furthermore, its specialised hindwing shape helped to extract lift from the wingtip vortex, adding to flight efficiency.”

Co-author Professor Wang Xiaoli from Linyi University in Shandong Province said: “The study made use of the latest anatomical insights from over 100 fossilised Microraptor specimens at the Shandong Tianyu Museum of Nature, including wing profile and body outline information only observable under Laser-Stimulated Fluorescence (LSF) imaging, providing a crucial basis for accurately reconstructing its body plan.”

Another co-author, Professor Shyy Wei, Professor Emeritus and former President of The Hong Kong University of Science & Technology (HKUST), currently Chair Professor at HKUST (Guangzhou) and a leading authority on avian aerodynamics, commented: “Microraptor appears to have specialised anatomically to more efficiently utilise highly unsteady airflow patterns and interactions between the forewings and hindwings.”

Implications for the evolution of flight

Professor Pittman added: “Our results suggest that effective utilisation of unsteady aerodynamic features was a crucial step in early flight evolution. Through wing shape specialisations and adjustments to the relative position and angle of their forewings and hindwings, early multi-winged dinosaurs experimented widely with flight. This likely paved the way for the evolution of the two-winged flight mode seen in modern birds that freed their legs to focus more on other functions including prey capture.” He added that this research pushes back the timeline for the discovery of complex aerodynamic features in flight and will help with further exploration of the different stages of flight evolution.

For the full research paper, please visit: https://www.pnas.org/doi/10.1073/pnas.2518106123

[1] In fluid dynamics, a vortex is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved.

[2] Downwash flows are the downward deflection of air caused by an object like a wing or rotor, essential for generating lift but also creating turbulence and affecting the effective angle of attack.

[3] First-principle NS equation-based numerical investigations use computational methods to solve the governing equations for fluid motion and simulate complex flows, focusing on accuracy, stability and physical realism, and often comparing results with theory or experiments for validation.