“Aviation” further development over 150 million years: In the course of their long reign over the air, the energy consumption of the pterosaurs has decreased, model calculations show. Only the group of record giants among the prehistoric fliers was an interesting exception, the researchers report.
The successful career of the pterosaurs began about 245 million years ago in the Triassic era. It was not a question of representatives of the dinosaurs, because the lines of development of both groups had already separated at that time. The pterosaurs were the first flying vertebrates in evolutionary history. They emerged from two-legged land animals that eventually developed structures made of thin skins on their forelegs that allowed them to take off. The concept was a resounding success – the pterosaurs advanced to become the rulers of the sky: Over the course of the next 150 million years they produced many species and subgroups that, like today’s birds, adapted to different ways of life.
On the trail of energy efficiency
“Some were only the size of a sparrow, while others had the wingspan of a light aircraft,” says Chris Venditti of the University of Reading. The pterosaurs did not become extinct either because they were “outdated models”: It was not until the inferno at the end of the Cretaceous Period about 66 million years ago that they forcibly swept off the stage of evolution. Much is known about the impressive flight abilities of the pterosaurs, but there are still many open questions about their development history. “For example, it is unclear whether and how their concepts have developed further in the course of evolution. Until now it was generally considered difficult to understand to what extent certain abilities of living beings became more efficient in the course of their developmental history, ”says Venditti.
As part of the study, he and his colleagues focused on examining energy consumption when moving in the air. In order to track down the changes in this flight efficiency in the pterosaurs, they developed a biophysical model of the energy consumption of the body structure adapted to flying, using data from today’s birds. They also recorded the wingspan and body size of numerous fossils from the pterosaur lineage. They then applied their biophysical model calculations to 75 pterosaur species. “Our method has enabled us to study long-term evolution in a completely new way by comparing living things in different stages of their evolutionary sequence over many millions of years,” says Venditti.
Always more sophisticated
As the researchers report, it became clear that at the beginning of the development history of the body structure that was adapted to flying, there was apparently still significant potential for optimization. The animals apparently took advantage of this: Natural selection increased flight efficiency more and more until the pterosaurs became extinct. They advanced from rather ineffective pilots who could only cover short distances to elegant aerial acrobats who could fly over long periods of time and long distances. It was also shown that this development was based on continuous improvements over a long period of time and not on sudden evolutionary steps, as was previously assumed. The bottom line from the models is that the pterosaurs adjusted their body shape and size in such a way that at the end of their 150 million year evolutionary history they used on average about 50 percent less energy than at the beginning.
As Venditti and his colleagues further report, however, there was one group of pterosaurs for which the rule did not apply: The representatives of the Azhdarchoidea showed no steady improvements for more energy efficiency in flight. This Cretaceous pterosaur group produced the largest beings that ever rose into the air: the famous Quetzalcoatlus was similar in size to a giraffe and had a wingspan of over ten meters. As the researchers explain, their results now match previous assumptions about the Azhdarchoidea’s way of life: “These are further indications that these animals, although they were well-versed fliers, probably spent a large part of their time on the ground. Therefore, adaptations for increasingly efficient flight anatomy probably didn’t offer them as much benefit as other pterosaurs, ”says co-author Joanna Baker of the University of Reading.
In addition to the concrete results, the scientists now see the importance of their study in the clarification of the potential of their research approach. “Until recently, paleontologists could only describe the anatomy of living things using their fossils and derive functions from them. Now we’re able to calculate the functional efficiency of extinct animals and compare them across evolutionary history to see how it changed, ”says co-author Mike Benton of the University of Bristol. His colleague Stuart Humphries from the University of Lincoln concludes: “One of the few things that have not changed in the last 300 million years are the laws of physics. It was fascinating to be able to use these laws to understand the evolution of flight in these amazing animals, ”says the biophysicist.
Source: University of Reading, technical article: Nature, doi: 10.1038 / s41586-020-2858-8