Scelidosaurus, Owen, 1859

SCELIDOSAURUS : HISTORICAL CONTEXT

The discovery of the earliest remains of Scelidosaurus occurred in the late 1850s as a result of the fossilcollecting activities of James Harrison (1819–64). Harrison was born in Purley, Surrey and studied medicine at St. George’s Hospital. Unfortunately, his health was too poor to allow him to complete his training ( Lang, 1947), so in 1850 he and his two sisters moved to the village of Charmouth, which is situated less than a mile along the coast east of Lyme Regis ( Fig. 1). He married a local woman (Miss Ludlam) in 1851 and they had two daughters. Given the recent (1847) death of the renowned local fossil collector Mary Anning ( Lang, 1947, Torrens, 1995), it is perhaps not at all surprising that Harrison developed an interest in collecting (or acquiring) fossils from the coast near Charmouth. This pastime seems to have been pursued actively until 1858, at which time Harrison became more seriously ill. He continued to acquire specimens from local quarrymen working the cliffs and maintained an active correspondence about them, but was reportedly bed-ridden from then until his death in 1864 at the comparatively young age of 45. The crumbling cliffs of Lias (see Fig. 2) are a prominent feature along the shoreline around Charmouth. These cliffs were a source of fossils and were also actively quarried in the middle of the 19 th century for the production of a superior quality ‘hydraulic’ cement manufactured at Charmouth. The Charmouth Heritage Coast Centre is built on the foundations of the original John Morcombe & Sons Hydraulic Cement Works.

Judged by the correspondence of the time, reported by William Dickson Lang (1947), Harrison collected together the initial dinosaur discoveries and sent them directly to London for identification by Richard Owen. The encouragement he received from Owen concerning the scientific importance of these bones prompted Harrison (who was invalid by then) to recruit quarrymen to search for further specimens. This resulted in the discovery of a number of associated marlstone slabs that enclosed the majority of a large skeleton of this animal ( Owen, 1863: 1; see Fig. 3). The Earl of Enniskillen (another avid fossil-collector and frequent visitor to the area) organized the transportation of the additional slabs to London for Owen’s attention. In 1861, negotiations between Owen and Mrs Harrison resulted in the large skeleton being bought by the British Museum for £50. However, additional portions of this animal were still being collected and sent to London until as late as August 1863 ( Lang, 1947). No further specimens were sold to the British Museum during James Harrison’s lifetime, but after his death in 1864, Mrs Harrison sold several additional fossils (listed in: Lang, 1947). Although most of these were invertebrate fossils, one notable specimen was the scelidosaur ‘type’ knee joint (NHMUK OR39496: see Norman (2020a)).

As eventually reported ( Owen, 1863: 1–2):

‘Following in the track opened out by the discovery of the skull described in the preceding Monograph [ Owen, 1861], about twelve successive blocks of Lias were secured, with more or less evident indications of included bones, all of which, together with the skull, have been purchased by the British Museum [ Fig. 3].… In the operation of clearing off the matrix, scattered dermal bones first presented themselves, and these were removed, with a note of their position, when it became plain that they did not touch or rest upon any part of the endo-skeleton. This being reached, the dermal bones in contact with it were left, save where they concealed some joint, process or other light-giving or characteristic part of the framework.’

The most distinctive feature of this dinosaur is its covering of bony dermal armour. Owen (1863: 20–26) described the portions that were preserved with the lectotype skeleton, but concentrated most of his effort upon the osteoderms attached to the tail because they were, overall, better preserved and more naturally positioned than elsewhere on the body. It is also clear from Owen’s descriptive account that mechanical preparation and removal of several osteoderms had been undertaken in order that the underlying skeletal bones could be described and illustrated. In summary, Owen (1863: 25) was able to observe that…

‘… the surface of the Scelidosaur was defended by several longitudinal series of massive dermal bones, those occupying the medial and upper surface being arranged in pairs [ Fig. 4] upon the nape and singly along the tail [ Fig. 5]. External to these were flattened, ovate scutes along the lower lateral series, at least two in number but probably more, on each side of the trunk, having the same wedged and ridged shape as the dermo-neurals [dorsally positioned median osteoderms seen in the tail]. Beneath these were flattened, ovate scutes along the lower lateral part of the thoracic-abdominal region. In the tail we have more decisive evidence of a single medial row of large, asymmetrical, cuneiform, hollow-based, superiorly ridged dermoneurals, with dimensions making three occupy the space of five vertebrae along the base of the tail, and nearly seven vertebrae along the hinder half of the tail. There was a corresponding median series of smaller and less vertically extended dermo-haemal [ventrally positioned median osteoderms] bones, and also a single series of dermo-laterals, of more depressed and fuller ovate form, on each side.’

On the basis of the trimmed and damaged array of osteoderms exhibited on the torso of the lectotype skeleton, Owen (1863: tabs III, VIII, IX; see Figs 4, 5) was able to determine that the pattern of osteoderm rows seen on the neck and torso (paired on either side of the midline) differs from that seen on the tail (median dorsals, ventrals and paired laterals). He also observed that the tail osteoderms do not diminish in size distally in proportion to the reduction in size of their underlying vertebrae. It is unfortunate that Owen made no attempt to reconstruct the skeleton of this dinosaur with its osteoderm covering. However, this accords with the general style of palaeontological description at the time. It was not until the work of O. C. Marsh (1881, et seq) that skeletal reconstructions became more commonplace.

Several caudal vertebrae that have been (largely) freed of matrix, following acid immersion, retain adherent osteoderms that display their general morphology (compare Figs 5 and 6). The larger carbonate-rich mudstone with thin, occasionally lenticular, marly limestone beds. The beds that have been reported to yield scelidosaur remains are Bed 83 – Stonebarrow Flatstones (Ian West; http://www.southampton.ac.uk/~imw/Lyme-Regis-to- Charmouth.htm) and Bed 85 – Topstones (David Sole, pers. comm. As also reported by Lang, 1947)

Sedimentary log conventions: pale even tone – carbonate-rich mudstone, fine horizontal shading – shale/mudstone, blocky and lenticular layers – marlstone/limestone.

osteoderms, which Owen described as being organized in longitudinal rows ( Fig. 3), have an oval base and the dorsal (external) surface has been seemingly pinched on either side and drawn upwards to form a raised, oblique, longitudinal ridge. Overall, their shape is reminiscent of a pup-tent ( Scheyer & Sander, 2004). The underside of these isolated, large, ridged osteoderms is excavated ( Owen, 1863: tab. VII, 3) and the inner surface mimics the general contours of the outer surface such that these osteoderms are thin-walled and cap-like.

It is unfortunate (but understandable, given the circumstances pertaining to the original excavation) that substantial portions of the dermal skeleton of the lectotype are either missing or represented by isolated specimens. Some were deliberately cut away during the preparation of the skeleton (under the supervision of Owen ), and it is likely that others were lost because they were not enclosed within the boundaries of the carbonate-cemented marlstone slabs that enveloped the majority of the buried skeleton. Nevertheless , it is clear from the appearance of some of the individual or fused arrays of scelidosaur osteoderms collected from Charmouth in subsequent years (and preserved among the collection of referred material at the Natural History Museum , London) – see inventory in Norman (2020a) — that their form and arrangement is more varied and complicated than originally described by Owen. Recent discoveries have added materially to our understanding of the morphological variation, distribution and growth of scelidosaur osteoderms .