866


Journal of Paleontology 89(5):845–869


line to the tip, and that a tendon was unnecessary. In addition, Bennett (2000) noted the curved fourth wing phalanges of some pterosaurs (e.g., Pteranodon) could not have borne the tensile loads that a trailing edge tendon would apply. Recently, Monninger et al. (2012) described what they


interpreted as a trailing edge tendon in a specimen of Rhamphorhynchus. They reconstructed it as extending from wing tip to ankle and suggested that it stabilized the trailing edge and contributed to camber control, but they did not explain how it would have functioned. I do not doubt that some pterosaur specimens preserve linear trailing edge features of some sort; however, the mere presence of a linear trailing edge feature in the brachiopatagium does not indicate that the feature was a discrete load-bearing structure. The actinofibril layer, the collagen fiber layer of the dorsal dermis, and the hypodermis each must have had a posterior margin, and the dorsal and ventral epidermis and dermis must have been continuous with one another, respectively, most of which need not have been coincident with each other or the posterior margin of the dactylopatagium, and all of these could have produced a linear trailing edge feature in a fossil preserving patagial soft tissues. A load-bearing trailing edge tendon would be compatible


with a wing in which the patagium was subjected to chordwise tension between the wing spar and tendon and the tendon rather than the patagium bore spanwise tension. However, it is incompatible with the interpretation presented here of a some- what stiff inextensible dactylopatagium and would place significant limitations on the shape and control of a tenopatagial plagiopatagium. It makes more sense to interpret the plagiopa- tagium as carrying spanwise tensile loads by way of collagen, elastin, and intrinsic muscle fibers spread across the chord of the plagiopatagium, which would provide greater control of the area and three dimensional shape of the plagiopatagium. Proponents of a load-bearing trailing edge tendon should provide evidence or argumentation for the presence and properties of the tendon and against alternative interpretations, and explain how it might have functioned within the context of the pterosaur patagium and flight.


Wing planform and flight.—Rhamphorhynchus has largely escaped the attentions of aerodynamicists, who prefer to con- centrate on the largest of pterosaurs, and there have been few reconstructions of the wing planform of Rhamphorhynchus (Fig. 9.1). Wellnhofer (1975) described the wing planform as narrow and scythe-like and illustrated it with the trailing edge following a smooth arc from the wing tip to near the hip joint. Padian and Rayner (1993) did not illustrate the planform, but presented schematic illustrations that showed a narrow and scythe-like wing similar to that illustrated by Wellnhofer. Bennett (2000) reconstructed the planform with the trailing edge following an S-curve from the wing tip to the proximal tibia based on the assumption that the dactylopatagium was exten- sible perpendicular to actinofibrils and with the patagium extended such that the length of the medialmost actinofibrils determined its chord posterior to the MCP joint. Here the plan- form is reconstructed based on the interpretation that the dac- tylopatagium was essentially inextensible and that the trailing edge of the plagiopatagium followed an arc of essen- tially constant radius to attach near the ankle as has been shown


by Elgin et al. (2011). The planform of the plagiopatagium is quite broad chordwise whereas that of the dactylopatagium is significantly narrower than previously thought. Note that there is no evidence that the trailing edge followed an arc of essen- tially constant radius, and if the trailing edge arc had a small radius behind the proximal antebrachium and increasing radii laterally to the dactylopatagium and posteriorly to the ankle, then the plagiopatagium would have a narrower chord and less area. In that case, control of the posterior part of the plagiopa- tagium by rotation of the femur about its axis for pitch control could have been more or less independent of the control of the area and shape of the rest of the plagiopatagium. One reviewer objected that the wing reconstruction


proposed here could not function in flight because wing area could not be reduced “to less than 50% of the fully extended area” whereas bats and birds can do so. Padian (1983a, 1983b, 1985, 1987a, 1987b, 1991) argued against bat-like interpreta- tions of pterosaurs as erroneous, but the bird-like interpretation of pterosaurs advocated in their place has proved to be similarly erroneous (e.g., pterosaurs were plantigrade quadrupeds [Lockley et al., 1995; Bennett, 1997a, b; Unwin, 1997] with the hindlimb fully involved in the wing [Elgin et al., 2011]). Pterosaurs were probably neither bat-like nor bird-like and differed from bats and birds as much as bats and birds differ from one another; therefore, there is no reason to think that pterosaur wings must have been functionally similar to bat and


bird wings. It is true that many birds can reduce wing area in flight; however, some birds (e.g., diomedeids, trochilids, sphe- niscids) do not reduce wing area significantly, and neither do insects including large (e.g., Titanus, Ornithoptera, the extinct Meganeuropsis [Beckemeyer and Hall, 2007]) and heavy species (e.g., Goliathus). Likewise, man-made ornithopters ranging from vonHolst’s (1957)model of Rhamphorhynchus andMacCready’s model of Quetzalcoatlus (Brooks et al., 1985; Cowley, 1986) to Festo’s Smartbird gull-like ornithopter (Mackenzie, 2012) have


successful flapping flight, the wing reconstruction proposed here would allow wing area to be altered. Contraction of intrinsic muscle fibers arranged subperpendicular to the trailing edge in the plagiopatagium could pull the trailing edge anteriomedially (large arrow in Fig. 9) reducing its chord and area. In addition, as discussed by Bennett (2000, p. 281–282), flexion of the shoulder, elbow, and wrist would reduce wingspan, and contraction of collagen, elastin, and intrinsicmuscle fibers in the plagiopatagium could reduce its area. Itwould also be possible to maintain tension on the medial margin of the dactylopatagium so as to keep it spread even if the plagiopatagium was lax and passively contracted. The only control envisioned by Bennett (2000) that would not be possible with the new interpretation would be decreasing the area of the dactylopatagium in flight.


Other pterosaurs.—Both Wellnhofer (1987) and Pennycuick (1988) noted linear features in the wings of the Vienna Pter- odactylus (NHMW 1975/1756/0000). Wellnhofer interpreted them as similar to what he thought was preserved on the Zittel wing, i.e., widely spaced cylindrical structures embedded within a bat-like extensible membrane. Pennycuick (1988,


demonstrated that the ability to alterwing area is not necessary for flapping flight. Thus, the reviewer’s objection is baseless. Although the ability to reduce wing area is not necessary for


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