Unique near isometric ontogeny in the pterosaur Rhamphorhynchus suggests hatchlings could fly

Abstract

Rhamphorhynchus muensteri is one of the best-known flying reptiles, represented by >130 well-preserved fossil specimens, from hatchlings to full adults. The life history of this pterosaur remains controversial as to when in ontogeny they took flight. Here, we assess the growth of these animals based on the lengths of numerous key elements. We show that changes in the skeletal anatomy of this reptile across its post-hatch size range reveal that R. muensteri exhibited overall near isometric growth in the wings, with slightly negative allometry in the humerus, radius and stronger negative allometry in the fourth metacarpal compared to body length, and slightly positive allometry in the second and third phalanges compared to body length. This pattern is near unique among flying vertebrates and suggests R. muensteri flew soon after hatching. In bats and birds, offspring do not typically fly until nearly adult sized. Conversely, near isometric growth in Rhamphorhynchus suggests it was a precocial flier and that individuals may have inhabited several sequential foraging niches over their lifespan, as some terrestrial and aquatic vertebrates do today.