N. Jb. Geol. Paläont. Abh. 284/2 (2017), 241–000 Article E Stuttgart, July 2017 Purported earliest bones of a plated dinosaur (Ornithischia: Stegosauria): a “dermal tail spine” and a centrum from the Aalenian- Bajocian (Middle Jurassic) of England, with comments on other early thyreophorans Peter M. Galton With 2 figures Abstract: The supposed base of a slender dermal tail spine from the Inferior Oolite Group (shallow marine deposit, early Middle Jurassic, Aalenian-Bajocian) of Dorset, England, previously reported as “Stegosaurus” and Thyreophora indet., is a half centrum of a caudal vertebra, Archosauria indet. A dorsally and ventrally incomplete vertebra from the same locality has a low centrum that is slightly wider transversely than it is long and, as there is a parapophysis anteriorly, it is part of a cervical vertebra. However, it does not match those of marine reptiles from the Middle Jurassic (Callovian) of England in which the cervical centra are elongate in crocodylomorphs, plate-like in ichthyosaurs, and short and wide in some sauropterygians (plesiosaurs and pliosaurs) but the parapophysis is mid-ven- trally situated. The Dorset centrum does not correspond to those of most contemporaneous dinosaurs, viz. theropods, basal sauropodomorphs, basal sauropods and ornithopods. However, it proportions correspond to posterior neck vertebrae of the basal thyreophoran Scelidosaurus (Lower Jurassic, England) and those of eurypod thyreophorans, the dacentrurine stegosaur Dacentrurus (described as Miragaia, Upper Jurassic, Portugal) and the nodosaurid ankylosaur Mymoorapelta (Upper Juras- sic, USA), so the Dorset centrum is tentatively identified as Thyreophora indet. The earliest skeletal records for armored dinosaurs are from the Middle Jurassic: for Eurypoda a proximal ulna from the early Bajocian of Scotland, for Stegosauria two large sub-vertically plates from the earliest Bathonian of England, and for Ankylosauria the ?Bathonian-Callovian of China or the early middle Callovian of England. However, the stegosaurian footprint taxon Deltapodus brodricki (Aalenian) of England pushes the origin of Stegosauria (and sister group Ankylosauria) down into the Early Jurassic. Key words: Thyreophora,uncorrected Euryopoda, Stegosauria, Ankylosauria, proofs Deltapodus, Sauropterygia, Jurassic, England, Portugal, USA, bones, footprints. 1. Introduction and from all continents except Antarctica and Austra- lia (GALTON & UPCHURCH 2004; MAIDMENT et al. 2008; The Stegosauria of MARSH (1877) is a clade of quadru- MAIDMENT 2010; GALTON 2012). pedal graviportal herbivorous ornithischian dinosaurs BENTON & SPENCER (1995: 125) listed “Stegosau- with a bizarre array of dermal plates and spines ar- rus” spines from a shallow marine deposit in the In- ranged as two rows along the top of the body from the ferior Oolite Group (Aalenian-Bajocian, early Middle neck to the end of the tail. The group is represented by Jurassic) of Bradford Abbas (National Grid Reference bones from the Middle Jurassic to the Late Cretaceous SY 5915) near Yeovil in Dorset, southern England. ©2017 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany www.schweizerbart.de DOI: 10.1127/njgpa/2017/0667 0077-7749/2017/0667 $ 0.00 2 P.M. Galton Fig. 1. A-K – Incomplete bones from Inferior Oolite Group (Aalenian-Bajocian, early Middle Jurassic) from Bradford Abbas near Yeovil, Dorset, England. A-F, purported “Stegosaurus” dermal tail spine, NHMUK PV R.6334, oriented as a spine (A) and as a half centrum of a caudal vertebra, Archosauria indet. (B-F), in A, C, lateral; B, articular end on (or proximal for spine) views; D-E, cross-sectional (with detail E) and F, ventral (or anterior for spine) views. G-K, incomplete posterior cervical vertebra, mostly centrum, Thyreophorauncorrected indet, ?Eurypoda indet., NHMUK proofs PV R.6336, in G, ventral; H, dorsal; I, anterior; J, right lateral and K, posterior views (J, K lit from above). L-N – Stegosaur Dacentrurus armatus (Upper Jurassic, England), holotype NHMUK PV OR46013, proximal end of left dermal spine in L, proximal; M, medial and N, cross-sectional views M, N from OWEN 1875). Abbreviations: c, facet for chevron; p, parapophysis; scale lines = 50 mm (A-D, F-N) and 10 mm (E). These bones were cited as stegosaurian by NAISH & don University from 1921 to 1951 (see PARRINGTON & MARTILL (2008: 616), so this would be the earliest re- WESTOLL 1974). There is no information on the position cord for stegosaur bones, but MAIDMENT et al. (2008) of these bones as found and they are the only ones in re-identified the spine as Thyreophora indet.; they also the WATSON Collection from this locality (S.D. CHAP- mentioned a fragmentary vertebral centrum and two MAN, pers. comm. 2016). The results of an examination indeterminate fragments. of these potentially important but previously unillus- These bones were collected and subsequently donat- trated bones is given here. ed in 1951 to the NHMUK by DAVID MEREDITH SEARES WATSON (1886-1973), a distinguished vertebrate pale- Institutional abbreviations: CAMSM, Sedgwick Museum, ontologist and professor at University College of Lon- Cambridge University, England; CV, Chongqing Museum of Purported earliest bones of a plated dinosaur (Ornithischia: Stegosauria) 3 Natural History, People’s Republic of China; EGSUS, Pa- The cross-section of the broken end is roughly U- laeoecological Collection, Environmental and Geological shaped (Fig. 1D), rather than sub-circular to oval (Fig. Sciences, University of Sheffield, England; MB, Museum 1N), so the presumed posterior outline is indeterminate. fur Naturkunde, Berlin, Germany; ML, Museu da Lourinhã, Portugal; MWC, Museum of Western Colorado, Grand Junc- Because the cited histology (Fig. 1D, E) matches that tion, Colorado, USA; NHMUK PV: Division of Vertebrate of a vertebral centrum, as does the morphology, R.6334 Palaeontology, Natural History Museum, London, England; is re-identified as the half centrum of a caudal vertebra SDM, Stroud and District Museum, Stroud, England; SGDS: (Fig. 1B-F). The form of the articular end surface cor- St. George Dinosaur Discovery Site at Johnson Farm, St. responds to that of a centrum and the oblique ventral George, Utah, USA; SM, Staffin Museum, Isle of Skye, Scot- land; USNM, National Museum of Natural History [formerly surface (Fig. 1C) has facets for a chevron (Fig. 1B). In United States National Museum], Smithsonian Institution, ventral view (Fig. 1F) the sides initially converge but Washington DC, USA. then diverge, as do the sides of a centrum, rather than continuing to converge distally as on a stegosaurian dermal spine (Fig. 1L, M; GALTON 2016). The original 2. Description and comparisons length of this centrum was at least twice its height (Fig. 1C), quite unlike the proportionally short caudal centra The bone fragments of BENTON & SPENCER (1995) were of stegosaurs in which the height exceeds the length identified as NHMUK PV R.6333-36 by MAIDMENT except in the most distal part of the tail (GILMORE 1914; et al. (2008: 386, but incorrectly cited as from Lower ZHOU 1984). More elongate caudal centra occur in many Jurassic) as follows: “R.6334 is a small fragment of a groups of dinosaurs (WEISHAMPEL et al. 2004) and in dermal spine. It is expanded slightly at the base and marine crocodylomorphs (ANDREWS 1913), so this half appears to be rounded in cross-section. R.6336 may be centrum is tentatively identified as Archosauria indet. a partial vertebral centrum, although (it) is extremely fragmentary. R.6333 and R.6335 are indeterminate NHMUK PV R.6336 (Fig. 1G-K): this is a ventrally bone fragments. Just a small part of the dermal spine incomplete vertebral centrum and, from the presence of is present, and morphologically it could be referable to a parapophysis anterodorsally (Fig. 1G-J), it is from a either Ankylosauria or Stegosauria. These elements are cervical vertebra. The centrum is slightly asymmetrical therefore regarded as Thyreophora indet.” in ventral view and amphicoelous (gently concave at both ends), with the maximum anterior width greater NHMUK PV R.6334 (Fig. 1A-F): as shown (Fig. than the length (Fig. 1G, H). Originally the centrum 1A) it looks like a stegosaurian dermal caudal spine was low, being wider than high (Fig. 1G, J), and it prob- but it differs from those of the stegosaur Dacentru- ably came from the posterior part of the neck. rus (Fig. 1L-N; Upper Jurassic, England; OWEN 1875; The Inferior Oolite Group (Middle Jurassic) of GALTON 1985, 2016) and Stegosaurus (Upper Jurassic, England is a marine deposit but the remains of marine USA; GALTON 2016). The proximal surface is smooth reptiles from it are rather limited, consisting mostly of (Fig. 1B), rather than being very irregular with foram- isolated bones and teeth of crocodylomorphs, plus frag- ina (Fig. 1L), and the rim is smoothuncorrected rather than be- ments of proofs ichthyosaurs, plesiosaurs and pliosaurs (BEN- ing indented by numerous grooves. The distal broken TON & SPENCER 1985). These groups are very well repre- cross-section (Fig. 1D, E) lacks a thick outer layer of sented in the more recent marine Peterborough Member compact bone bordering a well-defined central cavity of the Oxford Clay Formation (basal middle Callovian, as in Dacentrurus (Fig. 1N) and old adult individu- Middle Jurassic) of Fletton near Peterborough, England als of Stegosaurus (Upper Jurassic, USA; MAIN et al. (ANDREWS 1910, 1913). The crocodylomorphs do not 2005; HAYASHI et al. 2008, 2012). Instead it resembles have short cervicals. The ichthyosaurs have extremely the dermal spines of juvenile to young adult individuals short centra that are thick plate-like discs. Short wide of Stegosaurus and those of ankylosaurs in having a cervical centra occur in some sauropterygians (plesio- thin outer layer of compact bone bordering cancellous saurs and pliosaurs) but the parapophysis is situated bone, with no well-defined central cavity (HAYASHI et ventrally at mid-length, with the diapophysis some- al. 2010, 2012). Proximally this spine differs from those times fused to it dorsally (ANDREWS 1910, figs. 50, 51, of nodosaurid ankylosaurs from the Upper Jurassic of pl.