Scelidosaurus, : THE

Norman, David B, 2021, Scelidosaurus harrisonii (Dinosauria: Ornithischia) from the Early Jurassic of Dorset, England: biology and phylogenetic relationships, Zoological Journal of the Linnean Society 191 (1), pp. 1-86 : 38

SCELIDOSAURUS: THE

LOCOMOTOR SYSTEM

The biomechanical observations of Alexander (1976) followed by the review by Walter Coombs (1978c) prompted interest in the poses and relative proportions of dinosaur limbs, their musculature, locomotor capacity and trackway evidence (e.g. Gatesy, 1990; Carrano, 1998, 2000; Hutchinson, 2000a, b, 2004; Hutchinson & Gatesy, 2000; Carrano & Hutchinson, 2002; Hutchinson & Garcia, 2002; Sellers & Manning, 2007). Trackway evidence does not exist for Scelidosaurus but its appendicular skeleton is now known ( Norman, 2020b) and provides information concerning locomotor musculature, joint anatomy, limb proportions and potential limb excursion patterns for this animal.

PECTORAL GIRDLE AND FORELIMB MYOLOGY

The pectoral girdle and forelimb musculature of thyreophorans have rarely been considered. Coombs (1978b) attempted a reconstruction of the principal forelimb muscles in ankylosaurs. Norman (1986: figs 75–77) provided origin and insertion maps and a lines-of-action reconstruction for the musculature of the pectoral girdle and forelimb in the ornithischian ornithopod Mantellisaurus . These reconstructions were based on comparative myological information derived from extant crocodilians. Birds (although extant theropods) were considered too specialized in their pectoral anatomy and myology for meaningful comparison. Meers (2003) provided a beautifully crafted redescription of crocodilian forelimb musculature. Maidment & Barrett (2011) reviewed the identification of forelimb musculature in basal ornithischians (with occasional reference to the stem thyreophoran Scutellosaurus ) and used the Extant Phylogenetic Bracket (EPB) protocol advocated by Witmer (1995). Using this approach, they created origin and insertion maps for some of the shoulder and forelimb muscles of these dinosaurs based on a critical evaluation of the evidence of muscle distributions in living crocodilians and birds because they phylogenetically ‘bracket’ ornithischian dinosaurs. However, the efficacy of this approach is severely compromised by the profound differences between such disparate living representatives ( Romer, 1923b; Gatesy, 1990, 1995; Carrano, 2000). The EPB approach offers a logical basis for the prediction of some soft-tissue features in fossil animals, but its application in this instance requires the exercise of considerable caution. The anatomy of the pectoral girdle of Scelidosaurus resembles that described in other basal ornithischians ( Fig. 29 ) and this permits some plausible mapping of the origins and insertions of the principal support and locomotor muscles.

Figures

Figure 29. Scelidosaurus. Myological mapping. Scapula and coracoid, based on the lectotype NHMUK R1111 (A, lateral; B, medial). Humerus, based on the referred specimen BRSMG LEGL 0005 (C, posterior; D, anterior). After Norman (2020b: figs 56, 58,63).Abbreviations:bi, m.biceps; cuc,m.cucullaris;br, m.brachialis;dc,clavicular deltoid;ds, scapular deltoid; ld-tm, mm. latissimus dorsi-teres major; p, m. pectoralis; sbs, m. subscapularis; sh, m. scapulohumeralis; sc, m. supracoracoideus; scc, m. subcoracoideus; tra-ls, mm. trapezius-levator scapulae. Scale bars in centimetres.