Table 1.
Tabulation of specimens studied, selected elements, femoral length, and some particulars of specimens.
Figure 1.
Transverse histological sections under crossed polarizers, and corresponding interpretative drawings of early juvenile long bones of Rhamphorhynchus muensteri.
(A) The cortex of the tibia in the smallest studied specimen BSPG 1960 I 470a is dominated by immature fibrolamellar bone. It is noteworthy that already in this early ontogenetic stage endosteal bone rims the medullar cavity. (B) The femoral cortex of BSPG 1877 X I reveals more mature fibrolamellar bone with numerous longitudinal vascular canals resulting in high degree of porosity. Both specimens exhibit large, plump osteocyte lacunae.
Figure 2.
Histological sections of long bones of IPB 179 viewed with polarized microscopy.
(A) The femoral cortex shows three periosteal layers of different tissue types. Only a small portion of the oldest, innermost parallel-fibred layer with high vascularization degree is retained. The middle layer is a thick annulus formed of circumferential lamellae and numerous LAGs. The outer periosteal layer is parallel-fibred with moderately large osteocyte lacunae arranged in circular rows. The vascularity is locally different and some vascular canals open onto the periosteal surface. (B) Almost avascular, woven bone with a few deep intracortical LAGs makes up the bulk of the cortex of the tibia which is locally invaded by Sharpey's fibres.
Figure 3.
Ulnar histology of MTM 2008.33.1. under crossed polarizers.
Peripheral to the thick endosteal layer, extensive compacted coarse cancellous bone forms the middle layer of the cortex. Locally, the middle cortical layer consists of loose Haversian bone. The outer periosteal layer is composed of a strongly asymmetrical OCL.
Figure 4.
Histology of the III. phalanx of the wingfinger in MTM 2008.33.1. under normal polarized light and crossed nicols.
The medullary cavity is lined by a narrow layer of endosteal bone. The middle cortical layer is composed of loose Haversian bone. The outermost, primary layer is formed of sparsely vascularized fibrolamellar bone with one peripheral LAG.
Figure 5.
Femoral histology of MTM 2008.33.1. under normal polarized light and crossed nicols.
Thick endosteal layer merges into compacted coarse cancellous bone which forms the majority of the cortex. The periosteal outer layer is parallel-fibred, almost avascular with a few scattered secondary osteons and dense network of Sharpey's fibres.
Figure 6.
Histological sections of long bones of BSPG 1929 I 69 viewed with polarized microscopy.
(A) The femoral cortex has a very thick layer of endosteal lamellae. The parallel-fibred periosteal bone is moderately well vascularized by mostly longitudinal channels. Deep intracortical LAGs within three to four thin, lamellar-fibred annuli are present. (B) The medullar cavity of the tibia is lined by endosteal bone. The bulk of its cortex is composed of an almost avascular, parallel-fibred primary bone tissue with a few, widely spaced LAGs.
Figure 7.
Plot and regression of femoral length vs. estimated wingspan of 17 Rhamphorhynchus specimens.
Changes in the relation between these two traits during ontogeny can best be described by a power function in which high r2 value (p = 0.000) guarantees the reliability of the equation making wingspan estimations of specimens with missing wing bones possible.
Table 2.
Estimated wingspan and body mass of the five investigated specimens.
Figure 8.
Phylogenetic interrelationships, temporal ranges and general bone histological characters of different members of Pterosauria.
Taxa are specified at generic or family level. Taxa that have been histologically investigated so far are framed in rectangles. Those framed by rectangles of solid line have predominantly fibrolamellar bone of varying vascularity degree in the majority of the cortex, occasionally with LAGs and EFS indicating dramatic slowing down of growth in late ontogenetic stages, in which the onset of flight may have occurred. The two genera distinguished by frames of broken lines, Rhamphorhynchus and the ctenochasmatid Pterodaustro differ from the latter in revealing fibrolamellar bone only in juvenile stages and parallel-fibred bone with LAGs in later stages of development. We hypothesize that the early slowing down of growth in these genera is due to the relatively early onset of powered flight. Phylogenetic interrelationships without implications for divergence times are modified after [15] for non-pterodactyloids, and after [66] for Pterodactyloidea. Temporal ranges and chart are modified after [68]–[70].