Bennett—Rhamphorhynchus wings
849
identified, any interpretation of the specimen’s soft tissues as wing membrane is tenuous. Padian and Rayner (1993) presented a review of pterosaur
Figure 3. Schematic diagrams of cross-sections and dorsal surfaces of the brachiopatagium of Rhamphorhynchus.(1) Widely spaced cylindrical actinofibrils embedded within the patagium (after Wellnhofer, 1987); (2) widely spaced cylindrical actinofibrils on the undersurface of a patagium consisting of dorsal and ventral skins of epidermis (light gray) and dermis (medium gray) surrounding a common hypodermis (dark gray) core (after Padian and Rayner, 1993); (3) proposed model with closely spaced broad
lenticular actinofibrils within the dorsal epidermis and a layer of collagen fibers within the dorsal dermis forming the functional layer of a dactylopatagium consisting of dorsal and ventral skins of epidermis and dermis surrounding a common hypodermis core. Scale bar represents 1mm.
calcite that encrusted the original membrane,” but dismissed the striations as “bundled-up portions of contracted membrane.” Martill and Unwin (1989) described soft tissues from a
small section of a pterosaur specimen preserved in a concretion from the Santana Formation of Brazil, and interpreted them as consisting of the brachiopatagium near the ulna. They described a thin epidermis, a thicker dermis including a vesicular layer they compared to Böhm’s (1962) stratum vasculosum of Gallus, a layer of amorphous organic matter that they compared to Hildebrand’s (1988) stratum spongiosum, and a layer of closely spaced cylindrical structures they interpreted as muscle fibers. No actinofibrils were found. Martill and Unwin also did not find a second epidermis and dermis, which casts doubt on the interpretation of the specimen as wing membrane. Kellner (1996) had access to the remainder of the concretion from which Martill and Unwin (1989) obtained their section and argued that the soft tissues consisted of the skin and underlying musculature of the body wall behind the shoulder joint; in which case they would tell us nothing about the patagium. Unwin (personal
communication, 2013) now interprets the layer of muscle fibers as actinofibrils; however, their arrangement (tightly packed in a layer ~5 fibers thick) and position (deep to the dermis, in which case they would not be keratinous) is incompatible with most if not all interpretations of actinofibrils. Regardless, unless a second epidermis and dermis can be
wings and agreed with Wellnhofer (1975, 1987) that the raised longitudinal strips of the Zittelwing and the parallel striations of the Vienna Pterodactylus were the same, though they referred to them as structural fibers rather than as actinofibrils. They noted that pterosaur patagia would have consisted of dorsal and ventral skins of epidermis and dermis surrounding a common hypodermis core, and argued that the Zittelwing preserved the actual patagium rather than a positive impression of it and therefore that the actinofibrils were external. Furthermore, because the Zittel wing preserves the left wing in ventral aspect, they inferred that the actinofibrils were on the underside of the patagium (Fig. 3.2). Padian and Rayner stated that the actinofibrils were 0.05mm wide and were spaced from 3 to 8 per mm, and like Wellnhofer (1987) seem to have interpreted actinofibrils as present throughout the patagium (Padian and Rayner, 1993, fig. 14). They stated that some actinofibrils appeared to bifurcate near the trailing edge of the patagium, and suggested that this appearance resulted from the posterior end of actinofibrils having been detached from the underlying membrane and displaced laterally to expose the grooves in which the actinofibrils had lain. They also interpreted theMarsh specimen as preserving actinofibrils. Padian and Rayner noted a narrow band of tissue immediately behind the wingfinger and interpreted it as lying ventral to the actinofibril layer and as possibly involved in the formation of actinofibrils and their attachment to the wing spar. In regard to function, nowhere in Padian and Rayner’s paper is it stated or implied that tension within the patagium transmitted lift forces to the wing spar and body or that tension within the patagium enabled actinofibrils to transmit lift forces to the wing spar. Rather, although they did not use the word cantilever, it is implied that actinofibrils cantilevered the membrane behind the wing spar in the sameway that feather shafts cantilever the feathers’
vanes behind the forelimb in birds: “we argue that the structural fibers played a very similar role to bird feather shafts in transmitting aerodynamic force from the wing [sic] to the bones of the arm” (Padian and Rayner, 1993, p. 144), and “the wing-finger of pterosaurs had relatively little mechanical involvement in wing function” (Padian and Rayner, 1993, p. 140). Unwin and Bakhurina (1994) described and illustrated soft
tissue traces of the wings of Sordes pilosus Sharov (1971) from the Upper Jurassic Karabastau Formation of Karatau, Kazakhstan, which included long, straight, closely packed fibers in the chiropatagium behind the third interphalangeal joint and short multi-stranded fibers in the uropatagium. They suggested that the former fibers made the outer part of the wing stiff and relatively inelastic, but did not clearly state whether they interpreted the long and short fibers as the same or different. Bennett (2000) followed Wellnhofer (1987) in referring to
actinofibrils and brachiopatagium, and accepted that the raised longitudinal strips on the Zittel wing were actinofibrils that imparted special properties to the patagium, However, I rejected
the interpretation that the entire brachiopatagium bore actino- fibrils; rather I interpreted the pterosaur wing as Schaller (1985) had interpreted the wing of Sordes with a medial tenopatagial part and a lateral actinopatagial part. Perhaps I should have reverted to Wellnhofer’s (1975) term chiropatagium, but the membrane is no more a hand-wing than an arm-wing, and I was
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