Take-off is a vital part of powered flight which likely constrains the size of birds, yet extinct pterosaurs are known to have reached far larger sizes. Three different hypothesized take-off motions (a vertical burst jump using just the legs like those used by primarily ground-dwelling birds; a less vertical jump using just the legs more similar to the jump used by birds that fly frequently; and a four-limbed jump using its wings as well in a motion more like the take-off jump of a bat) have been proposed as explanations for how pterosaurs became airborne. Paleontologists from the University of Bristol, Liverpool John Moores University, the Universidade Federal do ABC and the University of Keele have constructed a computational musculoskeletal model of a 5-m wingspan ornithocheiraean pterosaur, reconstructing thirty-four key muscles to estimate the muscle moment arms throughout the three hypothesized take-off motions.
One second take-off sequences used in the study highlighting key phases: (A) bipedal burst style take-off with crouched, ankle lifted, and launch phase timings highlighted; (B) bipedal countermotion style take-off with countermotion and launch phase timings highlighted; (C) quadrupedal take-off style with crouch, vault, and launch phases highlighted. Image credit: Griffin et al., doi: 10.7717/peerj.17678.
“Powered flight is a method of locomotion that is limited to very few animals as it is energy intensive and requires specific adaptations to achieve launch, as well as deriving thrust and weight support via lift,” said Dr. Benjamin Griffin from the University of Bristol and his colleagues.
“The most power-intensive part of powered flight is take-off from the ground. This stage requires the animal to get high enough into the air to utilize an unobstructed flapping cycle.”
“Take-off also requires the animal to generate enough speed such that the wings produce enough lift to overcome drag (e.g., thrust) and support the weight of the animal.”
“The height and speed requirements both increase with larger size, making take-off size-limiting for flying animals.”
“No modern flying animal exceeds a mass of 25 kg with the heaviest volant living animal, the great bustard (Otis tarda), recorded as reaching 22 kg.”
“Despite this, many extinct animals have reached greater sizes and are still considered capable of flight, including birds such as Argentavis magnificens and Pelagornis sandersi which are predicted to have masses of 70 kg and 21.8-40 kg respectively.”
“Pterosaurs vary in size, with medium-sized pterosaurs reaching wingspans between 2 and 5 m predicted and masses ranging between 2 kg to 30 kg.”
“They have also reached the largest sizes of any animal considered volant with the largest pterosaurs such as Quetzalcoatlus northropi predicted to have reached much greater masses (150 kg, or more commonly 250 kg).”
“Flight at such large body masses challenges our understanding of the functional limits of flight making understanding take-off in pterosaurs crucial to establishing the functional limits of flight in organisms.”
The new study follows years of analysis and modeling of how muscles interact with bones to create movement in other animals and is now being used to start answering the question of how the largest flying animals known managed to get off the ground.
The authors created the first computer model for this kind of analysis of a pterosaur to test three different ways pterosaurs may have taken off.
By mimicking the motions, the researchers aimed to understand the leverage available to push the animal into the air.
“Larger animals have greater challenges to overcome in order to fly making the ability of animals as large as pterosaurs to do so especially fascinating,” Dr. Griffin said.
“Unlike birds which mainly rely on their hindlimbs, our models indicate that pterosaurs were more likely to rely on all four of their limbs to propel themselves into the air.”
The findings were published in the journal PeerJ.
_____
B.W. Griffin et al. 2024. Modelling take-off moment arms in an ornithocheiraean pterosaur. PeerJ 12: e17678; doi: 10.7717/peerj.17678
Source : Breaking Science News