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Swiss Journal of Geosciences

, Volume 103, Issue 2, pp 163–171 | Cite as

Exceptional stegosaur integument impressions from the Upper Jurassic Morrison Formation of Wyoming

  • Nicolai A. Christiansen
  • Emanuel Tschopp
Article

Abstract

Dinosaur skin impressions are rare in the Upper Jurassic Morrison Formation, but different sites on the Howe Ranch in Wyoming (USA), comprising specimens from diplodocid, camarasaurid, allosaurid and stegosaurian dinosaurs, have proven to be a treasure-trove for these soft-tissue remains. Here we describe stegosaurian skin impressions from North America for the first time, as well as the first case of preservation of an impression of the integument that covered the dorsal plates of stegosaurian dinosaurs in life. Both have been found closely associated with bones of a specimen of the stegosaurian Hesperosaurus mjosi Carpenter, Miles and Cloward 2001. The scales of the skin impression of H. mjosi are very similar in shape and arrangement to those of Gigantspinosaurus sichuanensis Ouyang 1992, the only other stegosaurian dinosaur from which skin impressions have been described. Both taxa show a ground pattern of small polygonal scales, which in some places is interrupted by larger oval tubercles surrounded by the small scales, resulting in rosette-like structures. The respective phylogenetic positions of G. sichuanensis as a basal stegosaurian and H. mjosi as a derived form suggest that most stegosaurians had very similar skin structures, which also match the most common textures known in dinosaurs. The integumentary impression from the dorsal plate brings new data to the long-lasting debate concerning the function of dorsal plates in stegosaurian dinosaurs. Unlike usual dinosaur skin impressions, the integument covering the dorsal plates does not show any scale-like texture. It is smooth with long and parallel, shallow grooves, a structure that is interpreted as representing a keratinous covering of the plates. The presence of such a keratinous covering has affects on all the existing theories concerning the function of stegosaurian plates, including defense, thermoregulation, and display, but does not permit to rule out any of them.

Keywords

Hesperosaurus mjosi Stegosauria Skin impressions Integument Keratinous covering Morrison Formation 

Institutional abbreviations

BRSM

Bristol’s City Museum and Art Gallery, England

SMA

Sauriermuseum Aathal, Switzerland

ZDM

Zigong Dinosaur Museum, China

Notes

Acknowledgments

We thank Hans-Jakob Siber (Sauriermuseum Aathal) for having invited us and encouraged our study on the stegosaurian integument impressions of the SMA. We are also grateful to the field team of SMA for having found and preserved the integument impressions, notably to the preparators Ben Pabst and Esther Premru. The manuscript benefited greatly from the comments and suggestions of Octávio Mateus (Universidade Nova de Lisboa; Museu da Lourinhã, Portugal), Rui Castanhinha (Instituto Gulbenkian de Ciência; Museu da Lourinhã, Portugal), James Farlow (Indiana University, Fort Wayne, Indiana, USA), and Stephen Brusatte (American Museum of Natural History, New York, USA) who kindly reviewed earlier versions of the manuscript, as well as of those of the two reviewers Matt Vickaryous (Department of Biomedical Sciences, University of Guelph, Ontario, Canada) and Kenneth Carpenter (College of Eastern Utah Prehistoric Museum, Price, Utah, USA). We are grateful to James Farlow, Shoji Hayashi, Octávio Mateus, Jesper Milàn, Kenneth Carpenter as well as Jacques Ayer for sharing their unpublished manuscripts with us, and for letting us incorporate some of their results into our work. We also thank Hans-Jakob Siber and Esther Premru for the permission to use their quarry map of SMA 0018, and Urs Möckli for providing us with high quality photos of the skin impressions.

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Copyright information

© Swiss Geological Society 2010

Authors and Affiliations

  1. 1.Museu da Lourinhã, Rua João Luis de MouraLourinhãPortugal
  2. 2.Faculdades de Ciências e TecnologiaUniversidade Nova de LisboaMonte de CaparicaPortugal

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