Hop, hop and away: On the take-off of Archaeopteryx using a multiple leaping mechanism.

Archaeopteryx, the iconic 150-million-year-old basal bird, lies at the heart of the debate on the origin of avian flight. While its asymmetric wing feathers indicate some flight capability, its limited shoulder mobility and reduced feather asymmetry suggest it lacked the capacity for the single, powerful leap used by modern birds for rapid take-off. Observations of extant birds reveal that many species, including corvids, employ multiple bipedal leaps with minimal wing assistance to gradually accelerate during take-off, particularly in low-stress contexts. Given Archaeopteryx's robust hindlimbs, we hypothesized that it could have used a similar multi-leap strategy to become airborne. We therefore tested the hypothesis that Archaeopteryx could generate sufficient take-off velocity via multiple hops or leaps. To test this, we developed a biomechanical model based on experimental take-off data from living birds, adapted to Archaeopteryx's anatomy. By analysing joint moments at the hip, knee, and ankle, alongside muscle capacity, we estimated its take-off velocity. Our results demonstrate that Archaeopteryx could have achieved its minimum sustainable flight speed in as few as two to three leaps, without requiring the energetically demanding single leap of modern birds. This study provides the first quantitative support for a ground-up, multi-leap take-off mechanism in early birds, distinct from the single-leap strategy usually observed today. We propose that the modern avian take-off may have evolved from this primitive multi-leap behaviour, offering new insights into the biomechanical transition from terrestrial locomotion to powered flight.