Scelidosaurus harrisonii, OWEN, 1861

SCELIDOSAURUS HARRISONII OWEN, 1861

Lectotype: NHMUK R1111 ( Charig & Newman, 1992; BZN, 1994). The remains of a medium-sized (5–6 m long), armoured ornithischian dinosaur comprising the skull, lower jaws (missing only the rostral portion of the snout) and the articulated postcranial skeleton (missing the majority of the cervical vertebral column and distal portions of both forelimbs).

Etymology: from Greek skelos (σκέλος) = limb or leg and sauros (σαυρος) = lizard/reptile. The epithet harrisonii refers to belonging to James Harrison, the collector. The generic name was probably chosen to distinguish this taxon from the paddle-limbed reptiles that predominate in the Liassic beds of the Charmouth/ Lyme Regis area.

Stratigraphic range: Charmouth Mudstone Formation (upper Sinemurian), Black Ven Marl Member, Asteroceras obtusum Zone, Obtusum Subzone. The nodule-bearing beds that occasionally reveal these remains are locally referred to as the Topstones Bed and the Stonebarrow Flatstones Bed ( Fig. 3).

There is a report of scelidosaur remains having been recovered from the base of the Pliensbachian of Seatown (Belemnite Marl Member, Uptonia jamesoni Zone ; Ensom, 1987), but their provenance cannot be confirmed, and it is considered likely that these specimens had eroded out of the cliffs at Charmouth and were carried to Seatown by longshore drift.

Locality: Cliff exposures on The Spittles–Black Ven between Charmouth and Lyme Regis, Dorset. Weathered nodules containing bones derived from cliff-falls are found occasionally along the foreshore beneath these cliffs ( Fig. 1) .

Diagnosis: (Postcranial only; the Diagnosis by Norman (in press) provides a synthesis of all skeletal autapomorphies.) Cartilaginous intercostal plates are attached to the largest dorsal ribs only. Caudal vertebra 1 has a convex posterior articular surface on its centrum, and caudal vertebra 2 is procoelous (note that this feature is not universal to all known skeletons and might represent a sexual dimorphism). Small fusiform clavicles are present on the pectoral girdle. An ovoid, convex ‘antitrochanter’ is present on the ilium. The prepubic process is comparatively short, rectangular in outline and twisted laterally. The proximal end of metatarsal 5 appears to have been sutured to the lateral margin of distal tarsal 4. Pedal digits 2–4 curve medially along their lengths. Pedal unguals 2–4 are graded in size: ungual 2 is largest, 4 is smallest (echoing the asymmetric structure seen in the manus). Pedal ungual of digit 1 is shorter, more nearly symmetrical, arched and bluntly pointed.

Differential postcranial osteology (relative to currently known thyreophorans, for which there is an abundance of postcranial remains): Small fusiform clavicles are present. Five disc-shaped carpals are present in the wrist. The phalangeal count for the manus is 2-3-4-3-2. Pointed unguals, but with a shallow arch, are present only on manus digits 1–3. The pubic shaft is rod shaped and longer than the ischium. The fourth trochanter is pendent. The astragalus and calcaneum cap the distal ends of the tibia and fibula and form a transverse roller joint. Two large distal tarsals are present (dT3 and dT4). Pedal unguals 2–4 are subconical, arched and curve medially along their lengths.

Inventory of the key postcranial material referred to in this monograph

A n u p -t o -d a t e l i s t i n g o f a l l p r e s e n t l y k n o w n scelidosaur material can be found in the first part of this monograph ( Norman, 2020).

1. NHMUK R1111 (lectotype) is the incomplete articulated skeleton of a large scelidosaur (estimated 4.4 m long). Missing parts of the postcranial endoskeleton include several cervical vertebrae and ribs, portions of the dorsal ribcage, some caudal vertebrae, parts of the pectoral girdle, both forearms and manus .

2. NHMUK R6704 is a small partial, articulated scelidosaur skeleton (~1.5 m long) of a juvenile individual (closely comparable in size to the associated paratype specimens, LYMPH 1998 6.1–6.7; see Norman, 2020) . The remains comprise the articulated midsection of the body: 13 dorsal vertebrae and their associated ribs, four sacral vertebrae and associated sacral ribs, seven caudal vertebrae (including 11 disarticulated caudal ribs), five chevron bones (haemal arches), ilia [right (r) and left (l)], pubes (r and l), ischia (r and l), femora (r and l), six lateral osteoderms and bundled broken lengths of ossified tendons.

3. CAMSM X39256 View Materials is the associated skeleton of a small scelidosaur (~2.1 m long). It includes some cranial fragments, the entire cervical, dorsal and parts of the sacral vertebral column, with a large number of cervical, dorsal and sacral ribs (many of which are complete). The appendicular skeleton includes parts of the pectoral and pelvic girdles, in addition to fragments of the proximal fore- and hindlimb bones.

4. BRSMG LEGL 0004 is the articulated skeleton of a large scelidosaur (~3.9 m long) and comprises some partly exposed parts of the presacral vertebral column, the shoulder girdle and proximal portions of the forelimb, most of the pelvic girdle and most of the hindlimbs (except for the distal halves of the metatarsals and phalanges of both feet) and the proximal part of the tail (the first 13 caudal vertebrae).SGDS 1311 is a cast of BRSMG LEGL

0004 constructed for public display. This specimen is an accurate reproduction of much of the original Scelidosaurus skeleton, but there are modifications and sculpted additions that create the impression that the skeleton is more complete than the original upon which it is based.

5. BRSMG LEGL 0005 is the partly articulated specimen of a scelidosaur (~3.1 m long), major parts of which have been fully prepared, while other portions remain embedded in marlstone. The specimen includes a fragment of the occiput and major parts of the precaudal axial skeleton and associated parts of both forelimbs, portions of the pelvis, sacrum and much of one hindlimb. There are also a few isolated proximal caudal vertebrae.

Reference will be made to two partial referred skeletons (BRSMG LEGL 0004 and 0005) collected from Charmouth in this monographic study. These specimens were collected (part paid for) and assembled by Mr David Sole (of Lyme Regis) during the 1990s and early 2000s. These specimens have collection numbers and are on permanent loan to the Bristol City Museum, where they are displayed and are functionally an integral part of the museum’s collections. Both specimens were removed from display for study in preparation for this monographic description, and are likewise available for study by other researchers (they have been on display and available for research at Bristol City Museum for nearly two decades). Mr Sole devoted decades of work (and some finance) to the collection and preparation of these specimens and is reluctant to relinquish ownership formally, at least for the time being.

ANATOMICAL PALAEONTOLOGY: AXIAL SKELETON

GENERAL COMMENTS

As a result of the preparatory work done on the lectotype ( NHMUK R1111 ; Fig. 2) and the two referred partial skeletons ( NHMUK R6704 and CAMSM X39256 View Materials ), it is now possible to describe most of the vertebral column in detail. These three skeletons overlap each other anatomically, allowing parts missing in one to be seen and described using the others. The lectotype is a medium-sized dinosaur (4.4 m long), yet one that reveals anatomical traces in the postcranium suggesting that it is ontogenetically subadult. The two referred specimens differ in size ( NHMUK R6704 , ~1.5 m long and CAMSM X39256 View Materials , ~ 2 m long) and are evidently juveniles. Despite the substantial differences in size between these specimens, the anatomical details displayed by their vertebral columns are remarkably similar. The other large but also subadult partial referred skeleton ( BRSMG LEGL 0004 , 3.9 View Materials m long) is notable because it closely resembles the lectotype, being preserved in a similar manner on a group of contiguous marlstone blocks that have been partly prepared. The preparation technique used on this additional specimen has exposed its remarkable and extensive dermal skeleton (Norman, in press) although this masks considerable portions of the underlying endoskeleton.A second smaller partial referred skeleton ( BRSMG LEGL 0005 ) preserves portions of the forelimb skeleton that have never been seen before .

An attempt has been made to draw comparative anatomical observations derived from personal observation and, in other instances, published accounts of basal ornithischians: Lesothosaurus Thulborn (1972) , supplemented by Santa Luca (1984) and Baron et al. (2017a), and Heterodontosaurus Santa Luca (1980) , supplemented by Sereno (2012) and Galton (2014). The remarkable anatomically conservative ornithopod Hypsilophodon ( Galton, 1974) has also been used where it seems appropriate to do so. The basal (non-eurypodan) thyreophoran taxon Scutellosaurus Colbert (1981) , supplemented by Breeden (2016), has been used, but it is unfortunate that so little is known of the postcranium of another basal thyreophoran, Emausaurus (Haubold, 1992) .

With regard to the more derived eurypodan thyreophorans (ankylosaurs and stegosaurs), it has to be stated that, with surprisingly few exceptions, anatomical descriptions of eurypodan taxa have tended to focus upon the cranium and are limited in scope with respect to the postcranial skeleton. The few exceptions that feature the postcranium are what might be considered the ‘classics’. For ankylosaurs, these comprise Lull (1921), Gilmore (1930), Russell (1940) and, much later, Coombs (1971), an abstract of which was presented by Coombs (1978a). Fortunately, this unbalanced approach has begun to be addressed in recent years ( Arbour et al., 2009; Arbour & Currie, 2016; Arbour & Evans, 2017). In the case of stegosaurs, the eponymous Stegosaurus was described in a monograph by Gilmore (1914), supplemented, in part, by Maidment et al. (2015), whereas the substantially earlier taxon, Huayangosaurus , was described by Zhou (1984), supplemented, in part, by Maidment et al. (2006).

CERVICAL VERTEBRAE