Take-off is a key part of powered flight and likely constrains the size of birds, although extinct pterosaurs are known to have grown to much larger sizes. Three different hypothesized take-off movements have been proposed to allow pterosaurs to fly: a vertical burst jump using only the legs similar to those used by mostly ground-dwelling birds, a less vertical jump using only the legs similar to those used by birds that fly frequently, and a quadruped jump using the wings as well in a movement similar to the take-off jump of a bat. Palaeontologists from the University of Bristol, Liverpool John Moores University, ABC Federal University and Keele University built a computational musculoskeletal model of an avian pterosaur with a five-metre wingspan, reconstructed 34 major muscles and estimated muscle moment arms across the three hypothesized take-off movements.

“Powered flight is a form of locomotion that is restricted to only a small number of animals because it is energy-intensive, requires specialized adaptations to take off and requires lift to support thrust and weight,” Dr Benjamin Griffin from the University of Bristol and his colleagues said.

“The most energy-intensive part of powered flight is take-off from the ground. During this stage, the animal needs to get high enough into the air to be able to utilize an unimpeded flapping cycle.”

“Take-off also requires the animal to gain enough speed so that the wings can overcome drag (i.e. thrust) and generate enough lift to support the animal's weight.”

“As size increases, so do altitude and speed requirements, limiting the takeoff size of flying animals.”

“Modern flying animals do not have a mass greater than 25 kg. The heaviest flying animals were Bustard (Otis Tarda)It was recorded to have weighed 22kg.

“Despite this, many extinct animals grew large bodies and are still thought to be capable of flight. Argentavis magnificens and Pelagornis sandersi They are predicted to have masses of 70 kg and 21.8 to 40 kg, respectively.”

“Pterosaurs vary in size, with medium-sized pterosaurs predicted to have a wingspan of 2-5 metres and weigh between 20 and 30 kilograms.”

“They also reached the largest sizes among the largest animals, such as pterosaurs. Quetzalcoatlus Northropii It is predicted to have reached a much larger mass (150 kg, or more commonly 250 kg).”

“Flight at such a large mass challenges our understanding of the functional limits of flight, and understanding pterosaur take-off is crucial for establishing the functional limits of biological flight.”

This new research follows years of analysis and modeling of how muscles in other animals interact with bones to produce movement, which are beginning to be used to answer the question of how the largest known flying animals were able to take off from the ground.

The authors created the first computer model of this kind for a pterosaur analysis, to test three different ways that pterosaurs might have taken flight.

By mimicking this movement, the researchers hoped to understand the leverage principles that could be used to propel the animal into the air.

“Larger animals have to overcome greater obstacles to fly, which is why the ability of large animals like pterosaurs to fly is particularly intriguing,” Dr Griffin said.

“Our model shows that unlike birds, which rely primarily on their hind limbs, pterosaurs likely relied on all four limbs to take to the air.”

of Investigation result Published in the journal Peer J.

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BW Griffin others2024. Modelling the take-off moment arm of an ornithosaur. Peer J 12: e17678; doi: 10.7717/peerj.17678