262


Journal of Paleontology 92(2):254–271 Prondvai et al. (2012) interpreted the transition to lamellar


Figure 7. Size-frequency histograms of samples of pterosaurs from the Solnhofen Limestone. (1) Rhamphorhynchus muensteri skull length (data from Wellnhofer, 1975; Bennett, 1995). (2) Pterodactylus antiquus skull length (data from Wellnhofer, 1970; Bennett, 2006, 2103a), gray bar at right is the adult from the Hienheim Beds. (3) Ctenochasma elegans skull length (data from Wellnhofer, 1970; Bennett, 2007a, 2013a). (4) Aurorazhdarcho micronyx humerus length (data from Wellnhofer, 1970; Bennett, 2006, 2013a), gray bars at right represent approximate size of Gnathosaurus subulatus Meyer, 1834 specimens known only from skulls. See text for explanation.


and medium year-classes of Rhamphorhynchus consist of small


immature and larger more-mature specimens, respectively, and the finding that the upper end of the medium year-class includes specimens with relatively mature histology and fused bones refines the interpretation.


bone with primary and secondary osteons in Rhamphorhynchus as resulting from the onset of flight based on comparisons to enantiornithine birds, and it was stated that juveniles would have been restricted to the ground and/or trees and would have received parental feedings or somehow fed themselves. There are several problems with that interpretation. It is not clear that the histological transition necessarily reflects anything other than a decrease in growth rate with increasing size, and there is no reason to think that pterosaur ontogeny would be comparable to that of enantiornithines (assuming that the relationship between ontogeny and histology in enantiornithines is correctly understood) because pterosaurs were not closely related to birds and are as different from birds and bats as birds and bats are different from each other. More importantly, the smallest, most immature specimens of Rhamphorhynchus were no more than a few weeks old, yet had skeletal anatomy and proportions similar to those of adults (Unwin, 2006; Lü et al., 2011). The long, well- ossified, although actively growing forelimb bones that would be subjected to bending loads in flight, extensive patagia (e.g., BSP 1938 I 503), and low wing loadings because of their small size indicate they were capable of powered flight. Prondvai et al. (2012) mischaracterized that interpretation as superprecociality (i.e., active locomotion within minutes of hatching), and argued against it and presumably precociality (i.e., relatively mature and mobile from hatching in contrast to the relative helplessness at hatching of altriciality) as well on the grounds that pterosaur eggs represented only a small investment of nutrients relative to maternal body size. Pterosaur eggs were not particularly small relative to maternal trunk volume (Unwin and Deeming, 2008; Lü et al., 2011), but it is the absolute rather than relative size that is important for precociality and some diapsids with relatively much smaller eggs produce super-precocial hatchlings (e.g., baby sea turtles dig out of the nest and sprint for the safety of the sea immediately after hatching, and baby crocodilians swim well immediately). Pterosaur hatchlings seem to have been precocial, but it is unlikely that they were superprecocial because of the tight folding of the wingfinger within the egg (Unwin and Deeming, 2008). In most pterosaurs, the wingfinger’s interphalangeal joints allowed only slight flexion and extension (Bennett, 2007b, 2013b), and so it probably took hours to days for the wingfinger and patagium to attain flight configuration. Prondvai et al. (2012) also suggested that hatchlings’ flight muscles would not have been powerful enough for flight, but there is no evidence of that because hatchlings of the superprecocial Australian Brush-Turkey, Alectura lathami Gray, 1831, can fly within 24 hours of hatching (Starck and Ricklefs, 1998; Dial and Jackson, 2011). Hatchling diapsids usually have residual yolk constituting ~10% of hatching mass that can sustain the individual for some weeks (Allsteadt and Lang, 1995; Tucker et al., 1998; Radder et al., 2007; Wolanski et al., 2007; Van Dyke et al., 2011), and it is conceivable that hatchling pterosaurs used such residual yolk


for some days of grounded flapping so as to attain the wing’s flight configuration, to exercise the pectoral musculature, and to train the neural control mechanisms needed for flight. The large fully formed wings of hatchlingRhamphorhynchus


and Pterodactylus are in marked contrast to the wings of neonate bats and most hatchling birds. The wings of Indian Pygmy Bat,


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