Bennett—Rhamphorhynchus wings Materials and methods


The Zittel wing (BSP 1880 II 8) and the Marsh specimen (YPM 1778) were examined with optical microscopes and photo- graphed with an 18 MP digital SLR camera and macro lens at minimum focal distance to produce several vertically overlapping rows of multiple laterally overlapping high- resolution images, which were composited into a single large TIFF photomosaic using Microsoft Image Composite Editor (Version 1.4.4.0, Microsoft Corporation, Redmond, WA). In the case of the Zittel wing, 130 overlapping images were compos- ited into a 422 MB TIFF photomosaic with a resolution of ~91 pixels/mm. The photomosaic images were temporarily divided into smaller sections in separate files that were pro- cessed using Paint Shop Pro 8 (Jasc Software, Minneapolis, MN) and Photoshop CS5 Extended (Adobe Systems, San Jose, CA) to map various features of the specimen (e.g., bones, raised longitudinal strips, folds) onto separate layers. Subsequently, the sections and layers were reassembled. As for terminology, on the limestone slabs places where


bones or soft tissues were pressed into the sediment at the bottom of the Solnhofen lagoons and produced a mold of the external surface of the underside of the structures (as a foot pressed into damp sand produces a footprint) are referred to as negative impressions. Similarly, where sediment covered over bones or soft tissues and produced a mold of the external surface of the upper side of the structures are referred to as negative impressions. Thus negative impressions may be on both the lower and upper slabs. Places where soft tissues were pressed into the sediment and produced a negative impression on the lower slab but decayed away so that the sediments that formed the upper slab filled the negative impression on the lower slab and produced an opposite and complementary shape (as plaster poured into a footprint takes a cast) are referred to as positive impressions. In some instances soft tissues may have resisted decay long enough to produce negative impressions on the lower and upper slabs but decayed away to leave a void between the slabs. Where waterborne minerals precipitated and filled the void, they produced a three-dimensional cast of the soft tissues that reproduces the shape of the soft tissues and the external surfaces of their upper and under sides. The term trace is used not in the sense of trace fossils, which typically preserve the interaction of a living organism with sediments (e.g., footprints, burrows), but rather as a more inclusive term for all sorts of evidence of soft tissues (e.g., impressions, brownish carbonac- eous organic films, fluorescence under UV illumination). Following Wellnhofer (1987) and Bennett (2000), the


terms propatagium, brachiopatagium, and uropatagium are used to refer to the parts of the patagium anterior to the forelimb, between the fore- and hindlimbs, and behind the hindlimb, respectively. Schaller’s (1985) terms plagiopatagium and dac- tylopatagium are used for the parts of the brachiopatagium behind the brachium through carpus, and behind the wingfinger, respectively, and Fold Line A is arbitrarily used as the dividing line between the plagiopatagium and dactylopatagium. The term actinofibril is restricted to the actual structural elements arran- ged in a posterolaterally radiating pattern within the dactylopa- tagium and lateral plagiopatagium that are considered to have imparted special properties to the dactylopatagium.


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Bennett (2000) thought that the significant difference between the medial and lateral parts of the brachiopatagium of Rhamphorhynchus was the presence and absence of actinofibrils and so used Schaller’s (1985) terms tenopatagium and actino- patagiumfor the medial and lateral parts of the brachiopatagium rather than for types of patagia as Schaller had used them. I now think that Schaller’s division into plagiopatagium and dactylo- patagiumbetter describes the difference between the medial and lateral parts of the brachiopatagium and so will use those terms and will not use tenopatagium and actinopatagium except in their adjectival forms in Schaller’s original sense for types of patagia. It is argued below that the raised longitudinal strips of Zittel (1882), which he and subsequent authors interpreted as structural fibers of some sort, are not traces of the actual structural fibers and so should not be called actinofibrils; therefore, I retain Zittel’s term. The term striae is used to refer to shallow epidermal grooves such as those that Marsh (1882) noted on the wings of YPM 1778. Prominent ridges or grooves in soft tissue impressions that resulted from the folding of the patagiumare referred to as folds, and linear features about which the patagium preferentially folded are referred to as fold lines. The band of soft tissue just behind the wingfinger (Padian and Rayner, 1993; Tischlinger and Frey, 2010; Monninger et al., 2010) is termed the retrophalangeal wedge. Following Wellnhofer (1975), filamentous structures protruding from the skin of Rhamphorhynchus are referred to as hair; the term pycnofiber (Kellner et al., 2010) does not apply because none of the filamentous structures seem to be branched.


Description of the Zittel wing


The Zittel wing (BSP 1880 II 8; Fig. 1) is an isolated left wing exposed in ventral view on the underside of an upper slab, fully articulated with the elbow, wrist, and fourth metacarpopha- langeal (MCP) joint flexed more or less as they might be for terrestrial locomotion, which preserves an impression of a seemingly undamaged patagium. The bedding plane of the specimen lay 5–7mm below the surface of the limestone slab, and in preparing the specimen the finder removed the covering matrix, scraped and smoothed the surrounding matrix for a distance of ~1–2.5 cm, and carved a beveled edge around the smoothed area. Note that there is no evidence that the scraping and smoothing altered the shape of the impression or removed any soft tissue traces. The left wing skeleton is essentially complete and articulated from the humerus to wing phalanx (WP) 4. The individual elements of the carpus are difficult to discern, the preaxial carpal and pteroid are anterior to the carpus with the pteroid directed medially. Metacarpals (Mc) I–III are displaced medially somewhat relative to Mc IV. Two phalanges of digits I–III are displaced near the base of Mc I, and one phalanx seems to be missing. Wing phalanges 1–4 are 105, 99, 90, and 91mm long, respectively, and the estimated wingspan of the specimen in life using my standard method (Bennett, 2001) is 102 cm. The brachiopatagium has a rounded tip of ~4mm radius and a gradually increasing chord as preserved of about 27, 39, and 44mm behind the third through first inter- phalangeal (IP) joints, respectively, which results in a trailing edge that is rather straight behind WP2–4 before arcing poster- omedially toward the hindlimb. Viewed from a moderate


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