古生物学：孵化したばかりの翼竜も飛べたかもしれない

Newly-hatched pterosaurs may have been able to fly but their flying abilities may have been different from adult pterosaurs, according to a study published in Scientific Reports.

Pterosaurs were a group of flying reptiles that lived during the Triassic, Jurassic and Cretaceous Periods (228 to 66 million years ago). Due to the rarity of fossilised pterosaur eggs and embryos, and difficulties distinguishing between hatchlings and small adults, it has been unclear whether newly-hatched pterosaurs were able to fly.

Darren Naish and colleagues modelled hatchling flying abilities using previously obtained wing measurements from four established hatchling and embryo fossils from two pterosaur species, Pterodaustro guinazui and Sinopterus dongi. The authors also compared these wing measurements with those of adults from the same species and compared the strength of the humerus bone, which forms part of the wing, of three hatchlings with those of 22 adult pterosaurs.

The researchers found that hatchling humerus bones were stronger than those of many adult pterosaurs, indicating that they would have been strong enough for flight. The authors also found that while hatchlings had long, narrow wings suited to long-distance flight, their wings were shorter and broader than those of adult pterosaurs, with a larger wing area relative to hatchling mass and body size. These wing dimensions may have may have made hatchlings less efficient than adult pterosaurs at long-distance travel, but may have resulted in them being more agile fliers, enabling them to suddenly change direction and speed.

The authors speculate that the agile flying style of hatchling pterosaurs may have enabled them to rapidly escape predators and made them better suited to chasing nimbler prey and flying amongst dense vegetation than adult pterosaurs. This could indicate that pterosaurs occupied dense habitats as hatchlings and open environments as adults, according to the authors.