Journal of Paleontology, 89(5), 2015, p. 845–869 Copyright © 2016, The Paleontological Society 0022-3360/16/0088-0906 doi: 10.1017/jpa.2015.68
New interpretation of the wings of the pterosaur Rhamphorhynchus muensteri based on the Zittel and Marsh specimens
S. Christopher Bennett Department of Biological Sciences, Fort Hays State University, Hays, Kansas 67601-4099, USA ⟨
cbennett@fhsu.edu⟩
core, and keratinous actinofibrils developed in place within the dorsal epidermis adjacent to a layer of linear collagen fibers in the dorsal dermis. The actinofibrils and linear collagen fibers together formed the main functional structure of the dactylopatagium. That structure made the dactylopatagium somewhat stiff and essentially inextensible so that it folded up along discrete fold lines that probably were genetically determined. A pneumatic retrophalangeal wedge behind the antebrachium through at least wing phalanx 3 streamlined the transition between the thick wing spar and thin patagium.
Abstract.—The Zittel wing of Rhamphorhynchus muensteri is reinterpreted as preserving negative impressions of closely spaced broad flat actinofibrils that were replaced by calcite but were prepared away by the specimen’s finder. The Marsh specimen preserves positive impressions of the dorsal and ventral surfaces of the wing, which show that the skin was smooth with fine wrinkles and that actinofibrils were not on the wing surface. Based on comparisons of those specimens, the dactylopatagium consisted of dorsal and ventral skins of epidermis and dermis surrounding a common hypodermis
Introduction
The wings of pterosaurs have intrigued researchers for more than 100 years, and one of the first found and most important speci- mens preserving evidence as to the structure of the pterosaur wing is the so-called Zittel wing of Rhamphorhynchus muensteri (Goldfuss, 1831). It is an isolated left wing skeleton exposed in ventral view, fully articulated with the elbow and wingfinger flexed, that preserves a seemingly undamaged wing membrane or patagium. Zittel (1882) described the specimen and noted a radiating pattern of fine, almost straight, raised longi- tudinal strips that nearly paralleled the wing phalanges in the lateral part of the patagium and became more anteroposteriorly angled in themedial part. He compared thewing to that of bats and
suggested that the strips functioned like the network of elastic fibers in bat wings. That same year, Marsh (1882) described another Rhamphorhynchus specimen that preserved soft tissues of the patagia, but mentioned only folds and fine striae that he interpreted as wrinkles. Subsequent authors ignored Marsh’s specimen and followed Zittel in interpreting the raised longi- tudinal strips of the Zittel wing as structural fibers of some type, termed them actinofibrils in recognition of their radiating pattern, and interpreted actinofibrils as internal, elastic, and forming a reinforcing systemwithin the patagium(e.g.,Wellnhofer, 1975) or as external, keratinous, and transferring lift forces to thewing spar (e.g., Padian and Rayner, 1993). I examined the Zittel wing in 1988 and 1993 and accepted
Padian and Rayner’s (1993) interpretation of the structure and position of actinofibrils. However, based on that interpretation
of structure I argued against previous interpretations of actino- fibril function and for an interpretation that actinofibrils pre- vented narrowing of the patagium under tension and redirected spanwise tension to the proximal wing phalanges,
reducing loads on the distal wing phalanges (Bennett, 1995, 2000). My interpretation of actinofibril function went largely unchallenged, but in 2008 I decided to reexamine the available evidence as to the structure of pterosaur patagia and photo- graphed the Zittel wing for high-resolution mapping of the distribution of actinofibrils and other structures. Subsequently, while processing the photographs and maps I became convinced that the raised longitudinal strips of the Zittel wing are not the actual structural elements that imparted special properties to the patagium (i.e., actinofibrils) preserved in place or positive impressions of such structures, but rather represent the spaces between negative impressions of the actual structural elements; so for 130 years we have misunderstood the Zittel wing’s message. This paper presents redescriptions of the Zittel wing and Marsh specimen, and a reinterpretation of the structure and relations of actinofibrils and the structure of the wings of Rhamphorhynchus based on those specimens. Note that the present paper is not a continuation of my previous paper on actinofibril function (Bennett, 2000); whereas that paper was a reinterpretation of function based on others’ interpretations of structure, the present paper is a reinterpretation of structure based on new examinations of important specimens.However at the end of this paper, I briefly review the interpretation of actinofibril function from my 2000 paper in light of the new interpretation of structure and present corrections necessitated by the new understanding of structure.
Institutional abbreviations.—BSP, Bayerische Staatssammlung für Paläontologie und Geologie, Munich, Germany; IVPP, Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, People’s Republic of China; JME SOS, Jura-Museum (Solnhofen Sammlung), Eichstätt, Germany; MB.R., Humboldt Museum, Berlin, Germany; MCZ, Museum of Comparative Zoology,HarvardUniversity,Cambridge,Massachusetts,U.S.A.;
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