古生物学：翼竜類の飛行

Pterosaur flight became more efficient as these flying reptiles evolved over 150 million years, a Nature study reveals. The research helps to resolve how the land-dwelling ancestors of pterosaurs took to the skies and then evolved further, and the methodology provides a blueprint for the nuanced study of functional and energetic changes through geological time.

Pterosaurs were close cousins of the dinosaurs. They evolved in the Triassic period (around 245 million years ago) and died out with the non-avian dinosaurs at the end of the Cretaceous period (around 65 million years ago), but fossils of the earliest pterosaurs remain elusive. This makes it hard to study how flight first evolved in this group. Using new statistical methods, biophysical models and insights from the fossil record, Chris Venditti and colleagues show that natural selection acted to increase flight efficiency in these animals constantly from their origin to their extinction. This changed them from ineffective flyers that could travel only short distances, to capable flyers that could have soared over long distances for extended periods of time.

There is, however, an exception to this pattern. The azhdarchoids were a group of gigantic Cretaceous pterosaurs that included Quetzlcoatlus and Tapejara. Their ability to fly is often debated because of various adaptations that hinted at a more terrestrial lifestyle. Here, the authors show that although azhdarchoids could fly, their flight performance did not increase over time, which suggests that flight efficiency was not as important to them as it was to other pterosaurs.