2024-10-21 19:00:00
In 2018, a South Korean team described the smallest known footprints attributed to a carnivorous dinosaur, likely a microraptor. These traces were discovered near the city of Jinju, in the south of the country. Measuring no more than a centimeter, they fossilized after the animal’s passage on the muddy banks of a lake more than 100 million years ago. Their discoverer, Kyung Soo Kim (Chinju National University of Education, Gyeongnam), noted that their spacing might suggest that the bipedal, sparrow-sized creature could approach at an impressive speed of 40 km/h (about 10 km/h). .5 m/s).
In a new study published Monday, October 21 in PNAS, collaborated with an international team to try to determine how such a small animal could run so fast. The conclusion? Perhaps it did not ultimately reach that speed, as its long stride was rather the result of using wing flaps to aid propulsion. A mode of movement that would shed light on the origin of flapping flight in birds – even if microraptors do not belong to the dinosaur lineage that generated them.
To reach this conclusion, the researchers started from a tool borrowed from fluid mechanics: it is a version of the Froude number which expresses a relationship between the speed of an animal and the size of the presumed limbs that push it, for a given gravitational force. In the case of the Korean footprints, Froude’s estimated number was 238, almost double that of the cheetah, the fastest land animal, while the ostrich is measured at 54 and man at 15, and that small dinosaurs hover we are a little higher.
“A brief impulse”
The bipedal movement of the microraptor at 10.5 m/s therefore did not seem realistic from a biophysical point of view: it would have required leg muscle strength unprecedented in the animal kingdom. However, we know that microraptors also have forelimbs covered in feathers. By introducing wings into the equation, “We found that the tracker could move at a much more reasonable speed (e.g., around 6 m/s) to produce the observed track, if its running benefited from the assistance of its wings”explains Michael Pittman (Chinese University of Hong Kong).
Did it proceed in leaps followed by a semblance of a glide? “What is likely, if it wasn’t trying to take off, is that the flapping of its wings gave it a brief impulse to accelerate much faster than without wings, perhaps to escape predators.”suggests his co-author Alexander Dececchi (Dakota State University, Madison). A behavior that would have put it on an evolutionary take-off path: starting from a certain speed, the wings would generate enough lift to escape gravity. “I calculated that a larger specimen – of the order of 1 kg compared to the 25 g of our microraptor – could fly away by flapping its wings at this speed of 10 meters per second”explains the researcher. For species weighing between 10 and 15 kg, which we know did not fly or glide, flapping might give a boost of the order of 10% to 25%.
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