Iguanodon hollingtoniensis (Lydekker, 1889)

Norman, David B., 2015, On the history, osteology, and systematic position of the Wealden (Hastings group) dinosaur Hypselospinus fittoni (Iguanodontia: Styracosterna), Zoological Journal of the Linnean Society 173 (1), pp. 92-189 : 93-97

I. HOLLINGTONIENSIS

Iguanodon fittoni was first announced in a short article that reported a series of (allegedly associated) specimens comprising a ‘... left ilium, part of a pubis [sic = ischium], and the imperfect sacrum (B.M. No. R.1635), which appear to indicate a distinct species’ ( Lydekker, 1889: 354).

These specimens were all collected from a site named Shornden or Shornden Quarry ( Fig. 1 ; Brooks, 2011; Norman, 2011a). This site probably derived its name from Shornden Forest, the southern edge of which contained early settlements in medieval times and was little more than a mile (1.6 km) north of what was later to become the coastal town of Hastings. Today, one street name and Shornden Reservoir appear to be the last reminders of Shornden as an actual location. Areas of land were routinely surface-quarried: stone (Tilgate Stone) was used for road mending, walling, and simple building work, whereas clay (Wadhurst Clay) was fired to make bricks, roofing tiles, and chimney pots. The remnants of much older quarries seem also to have pock-marked the district, reflecting the widespread extraction of Weald ironstone for an iron industry that had its origin in Elizabethan times ( Topley, 1875).

During the period 1850–1880 this area became the focus of considerable development as Hastings’ population expanded rapidly. One particular problem created by population growth was the need to provide an adequate water supply; this led to the conversion of the large, but probably long-exhausted, Shornden and Buckshole quarries into reservoirs ( Fig. 1 ). Abundant Wadhurst Clay would have been available to line these two sites and it seems that while these earthworks were being undertaken Dawson was on-hand to collect dinosaur remains. Other earthworks, associated with the construction of cuttings and embankments for the railway lines that extended to the coast from London; and, somewhat later, the creation of civic parkland during the 1880s [notably Alexandra Park, Coronation Wood, and Old Roar Ghyll (Gill) – Norman 2011a] provided further opportunities for fossil collection. Digging at the nearby Old Roar Quarry and Little Ridge Farm Quarry, as well as house building in and around the adjoining areas known as Hollington and Silverhill- Tivoli ( Fig. 1 ), created further opportunities for collecting. It is a source of considerable regret that no correspondence or notes (particularly between the key players: Dawson, Beckles, Owen, and Lydekker) detailing the excavation of these dinosaurs, have been discovered to date. Indirect comments by Richard Lydekker (originating from discussions with Dawson) hint at details of some excavations, and the direct quotation from a letter from Beckles to Richard Owen ( Owen, 1872) offers tantalizing snippets of information.

It was stated in Lydekker’s (1889) original article that the sacrum and ilium of I. fittoni were found on the same horizon, but separated by a distance of about 50 yards (∼ 45 m) and that the ilium represented part of an animal that was smaller in size than Iguanodon dawsoni (= Barilium dawsoni – Norman, 2010, 2011a, b, 2012). The latter species included an ilium that had been found at a slightly lower stratigraphical level in the same quarry. The ilium of I. fittoni was distinguished from the type specimen of I. dawsoni because it had a preacetabular process that was transversely compressed and lacked the pronounced medial ridge seen in the latter species ( Figs 3 , 9 , mr). The postacetabular portion of the ilium also differed significantly in shape: that of I. dawsoni having a deeper and more rounded profile, whereas in the new species the blade tapered to a rounded end that was expand- ed transversely, creating a pronounced brevis fossa ( Figs 3 , 9 , brf). Differences of proportion included the depth of the iliac blade above the acetabulum and the shape of the acetabulum; these, although mentioned as being ‘distinctive’, were ill-defined.

The preserved fragment of the sacrum exhibited transverse compression and fusion (both features found, according to Lydekker, in Iguanodon mantelli – based on comparison with NHMUK OR37685 – Owen, 1855: tables 3–6) but the latter species was reported to have a shallower iliac blade and to lack the pronounced brevis fossa seen in I. fittoni . The only other form to which this new species might be compared was Sphenospondylus gracilis Lydekker, 1888a [the generic name Sphenospondylus was originally proposed by Seeley (1883); Lydekker subsequently added the species name]. Sphenospondylus gracilis was based upon a series of dorsal vertebrae, so objective comparison was not possible, not that that fact inhibited Lydekker (1889: 354). In passing, Lydekker also noted that the ilium of I. fittoni bore some resemblance to those described as Camptonotus (= Camptosaurus ) from the Late Jurassic of North America ( Marsh, 1879); however, Lydekker also noted that the sacrum of I. fittoni could be distinguished from that of Camptosaurus because, unlike the latter, it had vertebrae that were fused together and bore ventral midline keels.

Iguanodon hollingtoniensis was briefly named and described in addition to I. fittoni . Lydekker established I. hollingtoniensis , using a partial skeleton recovered from the Wadhurst Clay at a site referred to as Hollington Quarry ( Fig. 1 ). He noted that some of this material had earlier been referred to either Iguanodon dawsoni , or as probable juvenile material of Iguanodon bernissartensis ( Lydekker, 1888a, b). The type material of this new species was regarded as ‘[NHMUK] R.1148 together with others belonging to the same individual numbered R.1629, and also certain vertebrae numbered R.1632, which are also believed to belong to the same individual’ ( Lydekker, 1889: 355). Additional material (NHMUK R811 and R604 – previously assigned by Lydekker to I. dawsoni ) was also transferred to this new species and another specimen, comprising a portion of a skeleton collected also at Hollington (NHMUK R33) was also mentioned as being referable to either I. fittoni or I. hollingtoniensis (but he, perhaps tellingly, was unable to confirm its specific identity).

Iguanodon hollingtoniensis was distinguished from I. mantelli by having a curved femoral shaft ( Fig. 4 ) and a pendant [incorrect] ‘inner’ (= fourth) trochanter. Both of these anatomical features had been reported as present in the femur of the smaller Late Jurassic Camptosaurus ( Marsh, 1879, 1885). The femur of I. hollingtoniensis was also described as ‘smaller and of different contour’ ( Lydekker, 1889: 355) compared with a femur associated with a partial skeleton that he attributed to I. dawsoni (by inference he appears to be referring to NHMUK R1627, a partial skeleton collected from Brede, a small village north of the Ore- Fairlight Anticline: see Fig. 1 ). The sacral vertebrae of NHMUK R811 (originally referred to I. dawsoni ), and those of NHMUK R1632 were described as ‘not anchylosed together’ (= unfused) and having flattened haemal (= ventral) surfaces; both of these features echoed those that had been described in Camptosaurus . An associated fragmentary ilium (NHMUK R811b) was described as having a preacetabular process of ‘the thin type of I. Fittoni , and therefore different from that of I. Dawsoni , while this ilium is decidedly different from that of I. Fittoni ’ ( Lydekker, 1889: 355). (N.B. The evidence used by Lydekker to support such a definite statement was never revealed.) Although alleged similarities with Camptosaurus were over-emphasized, the presence of the ‘peculiar pollex of Iguanodon ’ was used to support Lydekker’s reference of this new taxon to the genus Iguanodon .

Figures

Figure 1. The location of the town of Hastings within the county of East Sussex in the UK. Quarries (Q) and location names indicate sites that are known to have yielded Iguanodon-like ornithopod remains (most of which were collected by either Samuel H. Beckles or Charles Dawson). The ambiguity surrounding the location of ‘Hollington Quarry’ is genuine and reflects inconsistencies and vagueness introduced (probably by Dawson) when the documentation of these collections was being assembled in the late 1880s. Abbreviation: IoW, Isle of Wight.

Figure 3. Comparative ilia. A, Iguanodon (= Hypselospinus) fittoni NHMUK R1635, holotype in lateral view; B, NHMUK R1635 in medial view; C, Iguanodon (= Barilium) dawsoni NHMUK R802, holotype in lateral view; D, NHMUK R802, holotype in medial view. Abbreviations:?brf, brevis fossa non-existent (the area forming a smoothly curved overhang); brf, brevis fossa; lr, lateral ridge that demarcates the brevis fossa;?mr, medial ridge (much reduced); mr, medial ridge very prominent and forming an overhanging ledge; prp, preacetabular process; srf, sacral rib facet (prominent medially and clearly visible laterally). Scale bars = 10 cm.

Figure 4. Iguanodon hollingtoniensis (= Hypselospinus fittoni) holotype. NHMUK R1148. A, femur (right) nearly complete but crushed, as illustrated by Lydekker (1890a) (a, articular head; b, anterior trochanter; c, fourth trochanter, with exaggerated pendant tip; d, lateral distal condyle; e, medial distal condyle); B, C, the original specimen as preserved (May 2011) in dorsal and ventral views, respectively – the ventral view reveals the extent of longitudinal crushing postmortem. Abbreviations: 4t, fourth trochanter; at, anterior (lesser) trochanter; cr, crushing of the dorsal part of the medial condyle; icg, anterior intercondylar groove. Scale bar = 10 cm.

Figure 9. Iguanodon (= Hypselospinus) fittoni. Holotype NHMUK R1635. Ischium (right) proximal end, eroded. Abbreviations: ac, acetabular margin; obt, obturator process (eroded base). Scale bar = 10 cm.