With a 11 to 12-m wingspan, Quetzalcoatlus is the largest flying organism ever known and one of the most familiar pterosaurs to the public. First discovered in 1971, this pterosaur was thought to have flown over land using updrafts like condors and eagles. Conversely, Pelagornis sandersi (7 m wingspan), one of the largest extinct volant birds, was thought to have flown using dynamic soaring like albatrosses, using differences in wind speed with height above the sea surface. In a new study, scientists from Nagoya University, the University of Tokyo and the Centre d’Etudes Biologiques de Chizé used aerodynamic models to comprehensively quantify soaring performances and wind requirements of these extinct species and compared them with extant soaring birds. They found that Quetzalcoatlus was less suited to flying in updrafts than the extant birds, and Pelagornis sandersi was better suited to flying in updrafts above the sea, similar to frigatebirds, rather than using albatross-like dynamic soaring.
Flying animals have evolved a wide range of body sizes. Among them, there have been exceptionally large species of birds and pterosaurs.
Among the many extinct giant bird species, Pelagornis sandersi (from the Late Oligocene, approximately 25-28 million years ago) and Argentavis magnificens (from the Upper Miocene, approximately 6 million years ago) are the largest volant birds.
Their estimated wingspans reached 6-7 m, twice as large as that of the wandering albatross (Diomedea exulans), the living bird species with the longest wingspan.
Several large species of pterosaurs appeared in the Cretaceous period. Pteranodon, arguably the most famous pterosaur, is estimated to have had a wingspan of 6-7 m.
The azhdarchids are one of the most successful Cretaceous pterosaur groups and include several large species with wingspans of approximately 9-12 m.
Although their huge sizes have been led debate about whether they were flightless, Quetzalcoatlus northorpi, an azhdarchid species, is often regarded as one of the largest flying animals in history.
In the new study, Dr. Yusuke Goto from Nagoya University and the Centre d’Etudes Biologiques de Chizé and colleagues calculated and compared the ability of Pelagornis sandersi, Argentavis magnificens, Pteranodon, Quetzalcoatlus, the wandering albatross, the California condor (Gymnogyps californianus), the magnificent frigatebird (Fregata magnificens) and the kori bustard (Ardeotis kori) to soar using wind and air currents in an energy-efficient way.
“There are two types of soaring: thermal soaring, which uses updrafts to ascend and glide, such as eagles and frigatebirds; and dynamic soaring, which uses wind gradients over the ocean, as in the case of albatrosses and petrels,” the researchers explained.
They found that Pteranodon, for example, likely excelled at soaring flight using updrafts over the sea, flying in a similar way to the modern frigatebirds.
However, when they investigated the Quetzalcoatlus, they found that it was not suited for soaring flight even when atmospheric density parameters were changed.
“The poor thermal and slope soaring performance of Quetzalcoatlus was due to the large wing loading associated with their large body size,” the scientists said.
“This suggests that the wind conditions under which Quetzalcoatlus could conduct sustainable thermal soaring were limited.”
“Although it had previously been thought that Quetzalcoatlus was a proficient thermal soarer able to cover 16,000 km without touching the ground, our studies show that its thermal soaring abilities were below that of modern birds.”
“We suppose that the flight styles of Quetzalcoatlus and other similar sized pterosaurs were similar to those of the kori bustard that is a short-range flyer and spend most of their time on land.”
The team’s results also agreed with previous studies that Argentavis magnificens was suited to thermal soaring; on the other hand, they found that Pelagornis sandersi was suited to thermal soaring, although it was previously thought to use dynamic soaring.
“Our results demonstrate the need for comprehensive assessments of performance and required wind conditions when estimating soaring styles of extinct flying species,” the authors said.
The findings appear in the journal PNAS Nexus.
Yusuke Goto et al. 2022. How did extinct giant birds and pterosaurs fly? A comprehensive modeling approach to evaluate soaring performance. PNAS Nexus 1 (1): pgac023; doi: 10.1093/pnasnexus/pgac023
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