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. □ Bats, birds, ontogeny, precocial flight, pterosaurs.

Powered flight in hatchling pterosaurs: evidence from wing form and bone strength

“…The concept that pterosaurs were flightworthy from the moment of hatching is not new 4,6,7,12,19 but is supported here by the first quantified assessment of hatchling pterosaur flight performance and wing strength. We are doubtful of the suggestion that changing pterosaur growth rates were linked with the onset of powered flight 12 .…”

“…In these species, precociality means that the juveniles can follow and keep pace with their parents and other conspecifics; they do not live independently of them. Hone et al made essentially the same point 19 . Thus, an alternative interpretation of flightworthy anatomy in juvenile pterosaurs is that it perhaps gave hatchlings the capability to follow and associate with their parents or other conspecifics.…”

“…He further argued that this was the case for most other pterosaurs too. Hone et al 19 showed how skeletal proportions present across the ontogeny of Rhamphorhynchus are indicative of precociality and adult-like flight behaviour in hatchlings, and also suggested that different niches were occupied by this taxon across its ontogeny.…”

Multi-Aged Small Pterosaur Track Assemblage from the Upper Cretaceous of Korea

“…Moreover, many works regarding embryo fossils, growth rate, glide performance, and bone strength of pterosaur identi ed the possibility of precocial ight ability (e.g. [42][43][44][45][46] ), and gregarious nesting (e.g. 46 ).…”

“…Naish et al 46 compared the small-sized pterosaur (Sinopterus dongi) and medium-sized pterosaur (Pterodaustro guinazui) of hatchling and adult, and their wingspan hatchling-adult ratio is 7.6 and 10.34, respectively. Given the pterosaurs show isometric ontogeny 45 , the size of digits measured from tracks could re ect the hole size of the trackmaker. The result that the maximum-minimum ratio of pterosaur manus tracks (manus: 2.77; pes: 3.28) indicates that it covers a considerable portion of the entire pterosaur's life span.…”