Epidermal and Dermal Integumentary Structures of Ankylosaurian Dinosaurs Victoria M. Arbour, 1 * Michael E. Burns, 1 Phil R. Bell, 2 and Philip J. Currie 1 1 Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada 2 Pipestone Creek Dinosaur Initiative, Clairmont, Alberta T0H 0W0, Canada ABSTRACT Ankylosaurian dinosaurs are most nota- ble for their abundant and morphologically diverse osteoderms, which would have given them a spiky appearance in life. Isolated osteoderms are relatively common and provide important information about the structure of the ankylosaur dermis, but fossilized impressions of the soft-tissue epidermis of ankylosaurs are rare. Nevertheless, well-preserved integument exists on several ankylosaur fossils that shows osteo- derms were covered by a single epidermal scale, but one or many millimeter-sized ossicles may be present under polygonal, basement epidermal scales. Evidence for the taxonomic utility of ankylosaurid epidermal scale architecture is presented for the first time. This study builds on previous osteological work that argues for a greater diversity of ankylosaurids in the Dinosaur Park Formation of Alberta than has been traditionally recognized and adds to the hypothesis that epidermal skin impressions are taxonomically relevant across diverse dinosaur clades. J. Morphol. 000:000–000, 2013. V C 2013 Wiley Periodicals, Inc. KEY WORDS: Dinosauria; Ankylosauria; Ankylosauri- dae; osteoderms; skin; integument INTRODUCTION Integumentary impressions have been reported for nearly all major dinosaur clades, but are most commonly found in hadrosaurids (Davis, in press). Although the feathers of theropod dinosaurs receive much fanfare, there has also been impor- tant new work on the integument of ornithischian dinosaurs. Among ornithischians, epidermal scales predominate; however, at least two ornithischians, the heterodontosaurid Tianyulong and the ceratop- sian Psittacosaurus, preserve unusual filamentous structures similar to those found on many nona- vian theropods (Mayr et al., 2002; Zheng et al., 2009). Skeletal elements of the ankylosaur integu- ment, the osteoderms, which form in the dermis, are among the most commonly encountered anky- losaur fossils. However, epidermal preservation in ankylosaurs is comparatively rare. Ankylosaur skin impressions have been reported from only a few specimens: NHMUK R5161, Scolosaurus cut- leri Nopsca, 1928 from Dinosaur Provincial Park of Alberta (Nopcsa, 1928; Penkalski and Blows, 2013); ROM 784, Dyoplosaurus acutosquameus Parks, 1924 from the Dinosaur Park Formation of Alberta (Parks, 1924; Arbour et al., 2009); ROM 813, an indeterminate ankylosaurid from the Dinosaur Park Formation of Alberta (Penkalski, 2001; Arbour et al., 2013); and ZPAL MgD I/113, Tarchia gigantea (Maleev, 1956) from the Nemegt Formation of Mongolia (Arbour et al., 2013). Anky- losaur footprints bearing impressions of the integument have also been reported from a variety of Early and Late Cretaceous sites in western Canada and Alaska (McCrea et al., 2001). The histological structure of osteoderms has been used with some success to classify ankylo- saurs known from incomplete remains (Scheyer and Sander, 2004; Burns, 2008; Hayashi et al., 2010); however, virtually nothing is known about the taxonomic utility of epidermal structures (scales; Arbour et al., 2013). The most recent phy- logeny of the Amniota by Hill (2005) demonstrated that the incorporation of characters from the integument resolved relationships that other “traditional” anatomical characters could not. Recently, Bell (2012, in press) has shown that hadrosaurid skin impressions contain useful taxo- nomic information in both the morphology and arrangement of scales. Building on this, Arbour et al. (2013) briefly note integumentary differences between the ankylosaurid specimens ROM 813 (an indeterminate ankylosaurid from Alberta) and ZPAL MgD I/113 (cf. Tarchia gigantea). In this Contract grant sponsor: (VMA): National Science and Engineer- ing Research Council Canada Graduate Scholarship—Doctoral, NSERC Michael Smith Foreign Study Supplement; Alberta Ingenu- ity Studentship; Izaak Walton Killam Doctoral Scholarship; the Dinosaur Research Institute; the University of Alberta China Insti- tute; the Korea-Mongolia International Dinosaur Project; the Uni- versity of Alberta Graduate Students Association. *Correspondence to: Victoria M. Arbour; University of Alberta, Edmonton, Alberta T6G 2E9, Canada. E-mail: arbour@ualberta.ca Received 25 February 2013; Revised 14 June 2013; Accepted 9 August 2013. Published online 00 Month 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/jmor.20194 V C 2013 WILEY PERIODICALS, INC. JOURNAL OF MORPHOLOGY 00:00–00 (2013)