Stenopelix valdensis Meyer, 1859

Butler, Richard J. & Sullivan, Robert M., 2009, The phylogenetic position of the ornithischian dinosaur Stenopelix valdensis from the Lower Cretaceous of Germany and the early fossil record of Pachycephalosauria, Acta Palaeontologica Polonica 54 (1), pp. 21-34 : 22-24

Stenopelix valdensis Meyer, 1859

Figs. 1–6 .

Holotype: GZG 741/2 (formerly GPI Gö 741−2), impressions in sandstone of a partial articulated skeleton in dorsal and ventral views, including at least 13 dorsal vertebrae, five or six sacral vertebrae, more than 30 caudal vertebrae, ribs, ossified tendons, distal left scapula, distal left humerus, left radius, left ulna, left metacarpal 1, left and right ilia, pubes, and ischia, left femur, proximal right femur, left and right tibiae, fibulae and proximal tarsals, complete right pes and partial left pes.The holotype represents a small individual (less than one metre in length); subadult status is suggested by the absence of fusion between neural arches and centra, adjacent sacral centra, and sacral/caudal ribs and neural arches.

Type horizon and locality: Obernkirchen Sandstone (Early Cretaceous:

Berriasian; Schmidt 1969), near Bückeburg, Lower Saxony, NW Germany.

Emended diagnosis.—Small ornithischian dinosaur with the following autapomorphies: postacetabular process of ilium tapers uniformly to a rounded point; ischial blade with distinct bend at mid shaft; ischial blade is broadest at mid shaft, tapers proximally and distally; prominent proximodistally extending ridge present on the medial surface of the proximal 50% of the shaft of the ischium; distal end of ischial blade is arched dorsoventrally, with a convex lateral surface and a concave medial surface (modified from Sereno 1987).

Comments.— Sereno (1987) provided the first formal diagnosis for Stenopelix , based upon five autapomorphies, although these autapomorphies were neither described nor discussed. The first of the autapomorphies proposed by Sereno (1987) refers to the morphology and length of the postacetabular process of the ilium ( Fig. 2 ). The relatively short postacetabular process probably represents an ornithischian plesiomorphy (see below), but the uniformly tapering form of the process does appear to be unique.

Three of the autapomorphies proposed by Sereno (1987) refer to the morphology of the ischia ( Figs. 3 , 4 ), and a fourth ischial autapomorphy is added here. The ischia of Stenopelix are highly unusual and are marked by a distinct and prominent bend at mid shaft ( Fig. 4 ). At this point the ischial blade is at its broadest, and it tapers both proximally and distally from this point. As noted by Sues and Galton (1982), but not by Sereno (1987), there is a prominent ridge present on the medial surface of the proximal half of the ischial shaft ( Fig. 3 ). Distally, the ischial blade is transversely compressed, and is arched dorsoventrally, with the lateral surface convex and the medial surface gently concave.

The last of the possible autapomorphies listed by Sereno (1987) refers to the dorsoventrally compressed prepubic process. As discussed by Sereno (1987), the prepubic process of Stenopelix ( Figs. 1D , 3B ) is considerably longer than reconstructed by Galton and Sues (1982), appears to be strongly dorsoventrally compressed, and tapers slightly anteriorly. The strong dorsoventral compression of the process is not considered here to be autapomorphic for Stenopelix : a similar strongly dorsoventrally compressed prepubic process is also known in Yinlong ( Xu et al. 2006: fig. S2F), Archaeoceratops (IVPP V11114) and Psittacosaurus ( Sereno 1987; Averianov et al. 2006).

Figures

Fig. 1. Ornithischian dinosaur Stenopelix valdensis Meyer, 1857, holotype (GZG 741/2, formerly GPI Gö 741−2), from the Obernkirchen Sandstone (Early Cretaceous: Berriasian), near Bückeburg, Niedersachsen, Germany. A. Large sandstone slab. B. Interpretative outline drawing of large latex cast (prepared from large sandstone slab), showing majority of postcranial skeleton in dorsal view. C. Small sandstone slab. D. Interpretative outline drawing of small latex cast (prepared from small sandstone slab), showing sacrum and caudals, pelvic region and partial hindlimbs in ventral view. For clarity elements in and around the sacral region have not been labelled—these areas are shown in greater detail in Fig. 3. Roman numerals II–IV correspond to respective digits. Abbreviations: mt, metatarsals; f, femur;?, unidentified element.

Fig. 2. Ornithischian dinosaur Stenopelix valdensis Meyer, 1857, holotype (GZG 741/2, formerly GPI Gö 741−2), from the Obernkirchen Sandstone (Early Cretaceous: Berriasian), near Bückeburg, Niedersachsen, Germany. Latex cast of right ilium (large slab) in lateral view.

Fig. 3. Ornithischian dinosaur Stenopelix valdensis Meyer, 1857, holotype (GZG 741/2, formerly GPI Gö 741−2), from the Obernkirchen Sandstone (Early Cretaceous: Berriasian), near Bückeburg, Niedersachsen, Germany. Latex casts of sacral region. A. Large slab, dorsal view. B. Small slab, ventral view. Abbreviations: na, neural arches and spines; s1, s2, s3, s4, s5, sacral centra;?s6, possible 6th sacral centrum (may instead represent first caudal centrum); sr, sr1, sr2, sr5, sacral ribs; sr6, possible 6th sacral rib (may instead represent first caudal rib).

Fig. 4. Ornithischian dinosaur Stenopelix valdensis Meyer, 1857, holotype (GZG 741/2, formerly GPI Gö 741−2), from the Obernkirchen Sandstone (Early Cretaceous: Berriasian), near Bückeburg, Niedersachsen, Germany. Latex cast of ischia (small slab, both ischia are exposed in lateral view, anterior is to the right). Note the pronounced bend along the dorsal edge of the bone (arrows). Sacral and caudal centra between the ischia are exposed in ventral view.

Fig. 5. Ornithischian dinosaur Stenopelix valdensis Meyer, 1857, holotype (GZG 741/2, formerly GPI Gö 741−2), from the Obernkirchen Sandstone (Early Cretaceous: Berriasian), near Bückeburg, Niedersachsen, Germany. Latex cast of distal left scapula and associated elements of the forelimb (large slab).

Fig. 6. Ornithischian dinosaur Stenopelix valdensis Meyer, 1857, holotype (GZG 741/2, formerly GPI Gö 741−2), from the Obernkirchen Sandstone (Early Cretaceous: Berriasian), near Bückeburg, Niedersachsen, Germany. Latex cast of right tibia and fibula, partial right femur, and right pes (large slab). Tibia and fibula are exposed in posterior view; pes is exposed in anterior view. Note first phalanx of digit I. Roman numerals I–IV correspond to respective digits.