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858


Journal of Paleontology 89(5):845–869


much more resistant to decay than other soft tissues and so were probably coarse, leathery, and tough. However, the plagiopata- gium is less often preserved than the dactylopatagium (e.g., largely absent in the Marsh specimen and most other specimens that preserve traces of the brachiopatagium), and when it is preserved as in the Zittel wing, it provides little information about its structure and so it probably was not significantly more resistant to decay than other soft tissues. Therefore, it seems that Wellnhofer’s characterization as coarse, leathery, and tough probably applies primarily to the dactylopatagium. The plagio- platagium and dactylopatagium will be discussed separately, and the dactylopatagium will be considered first. The soft tissue impressions of the dactylopatagia of the Zittel


wing and Marsh specimen are distinctly different from one another, the Zittel wing being dominated by raised longitudinal stripswhereas theMarsh specimen is dominated by fine striae that are clearly not impressions of raised longitudinal strips, and this even though the impressions of both specimens are associated with articulated wing skeletons preserved on the underside of upper slabs (the hangende Platte of Barthel, 1978) formed by sediments laid down on top of the wing skeletons and their soft tissues. In order to reconcile the differences and properly interpret the raised longitudinal strips, it is necessary to consider themanner in which each specimen preserves what it preserves. Soft-tissue traces in the Solnhofen Limestone may be


produced in various ways. In some cases, soft tissues are pre- served as organic films that usually appear as brownish deposits under visible light and often fluoresce under UV light. The isolated Archaeopteryx feather and Pterodactylus antiquus specimens BSP 1929 I 18 (Döderlein, 1929b; Bennett, 2013a) and BSP 1883 XVI 1 and MCZ 1505 (Wellnhofer, 1970; Bennett, 2013a) are examples of such preservation. In other cases, the surface structure of the soft tissues that came to lie on the substrate is preserved as a negative impression on the lower slab, which in turn produced a complementary positive impression of those soft tissues on the upper slab. An excellent example of this is seen in the feathers of the Berlin Archae- opteryx (Rietschel, 1984), but among pterosaurs the occipital lappet of Pterodactylus antiquus (Wellnhofer, 1970; Bennett, 2013a) is preserved as a negative impression on the lower slab (MCZ 1505) and a positive impression on the upper slab (BSP 1883 XVI 1). Lastly, soft tissues that resisted decay may be permineralized or replaced by calcite to produce a three dimensional cast of their structure, which if removed will expose negative impressions of the upper and lower surfaces of the soft tissues on the upper and lower slabs, respectively. In pterosaurs, the cartilage in joints and the incompletely ossified articular ends of long bones are commonly replaced with calcite, which often obliterates the morphology; however, keratinous structures such as claw sheathes (e.g., Archaeopteryx, Wellnhofer, 2009) and the horny covering of the cranial crest (e.g., holotype of Ctenochasma porocristata Buisonjé 1981, JME SOS 2179; Buisonjé, 1981; Bennett, 2002) may also be preserved in this manner. It is not clear whether the soft tissues that resisted decay lasted long enough for there to be some permineralization or they decayed completely leaving a void in the sediments in which a calcite cast formed, but for convenience this type of preservation will be referred to here- after as replacement by calcite.


tion as an organic film and as an impression. The organic film is rather faint and does not seem to provide useful information as to the structure of the brachiopatagium whereas the impression is a positive impression of soft tissues including fine striae and fold lines on both wings. Padian and Rayner (1993, fig. 9) described and illustrated the left wing as preserving clearly visible structural fibers, yet there are no raised longitudinal strips like those of the Zittelwing and the striae cannot represent actinofibrils because they lack the straightness and regularity of the Zittel wing’s raised longitudinal strips and are much more widely spaced (~8 striae per 5mm in the Marsh specimen’s medial left dactylopatagium vs. ~5 strips per mm in the larger Zittel wing). Moreover, the fact that the impressions of the dorsal surface of the left wing and the ventral surface of the right wing both exhibit striae demonstrates that the striae cannot be traces of structural fibers that were present on only the ventral surface of the wing. Instead, their size and shape indicate that the striae are wrinkles in an otherwise rather smooth epidermis. However, there are two areas on the left wing impression that differ from the smooth epidermis; one just behind WP1 is interpreted as preserving a trace of the retrophalangeal wedge whereas the other near the medial edge of the left dactylopata- gium is interpreted as a small section of folded patagium sitting on top of the main impression (Fig. 8). In the case of the Zittel wing, there is evidence of all


The Marsh specimen exhibits a combination of preserva-


three types of preservation. The plagiopatagium exhibits a combination of preservation as an organic film and as a positive impression of soft tissues on an upper slab. The organic film is present in the medialmost parts of the plagiopatagium and preserves traces of fine hairs that covered the body whereas the positive impression seems to reflect a strongly contracted tenopatagial membrane and does not provide information as to its structure or properties other than the fact that it was capable of much contraction. The preservation of the dactylopatagium is more complex. In the central area of the dactylopatagium (i.e., posterior to the retrophalangeal wedge, >1.5cm anterior to the trailing edge, and behind WP1–3) the presence of the small calcitic fragment preserved within a groove between two raised longitudinal strips behind the middle of WP3 (Fig. 4) demon- strates that there was soft tissue preservation of resistant structures by replacement by calcite, with calcite casts pre- sumably formerly covering the entire central area of the dacty- lopatagium. As a result, the pattern of raised longitudinal strips bounding broad grooves must be interpreted as a negative impression of closely spaced broad flat structures rather than as a positive impression of widely spaced cylindrical structures. In addition, the lapstrake appearance of part of the central area is


consistent with a negative impression of closely spaced broad flat structures but inconsistent with a positive impression of widely spaced cylindrical structures. Two reviewers stated that they prefer to interpret the raised


longitudinal strips of the Zittel wing as preserving a positive impression rather than a negative impression. This is not sur- prising given that the human mind tends to interpret concave faces as convex (i.e., the hollow mask illusion, Gregory, 1997), and that the illusion is not limited to faces and the interpretation of objects as convex or concave is influenced by our knowledge of, or assumptions as to, the structure of the


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