Hypselospinus fittoni (Lydekker, 1889)
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publication ID |
https://doi.org/ 10.1111/zoj.12193 |
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persistent identifier |
https://treatment.plazi.org/id/03F9879B-3254-FF90-FC71-F912FCC67A0A |
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treatment provided by |
Felipe |
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scientific name |
Hypselospinus fittoni |
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1. NHMUK R604 & R604a
A partial skeleton collected by Dawson from Hollington quarry (old specimen cards associated with this collection of bones indicate that it was collected at Ridge Farm quarry). Most of this collection represents the vertebral column: one cervical centrum and fragments of a neural arch, 12 dorsal vertebrae, 16 caudal vertebra, several fragmentary ribs, and the proximal end of a chevron bone. Other associated remains include: three worn and somewhat damaged maxillary crowns, a well-preserved pollex ungual, a partial ulna, and some bones of the pes. The specimen was initially referred to I. dawsoni by Lydekker (1888a, b), but a little later Lydekker (1889: 355) transferred it, without explanation, to I. hollingtoniensis .
Axial skeleton
The cervical fragments exhibit typical features such as opisthocoely of the centrum, a thick ventral keel, and a parapophysis located, just posterior to the margin of the convex anterior articular surface, at midcentrum height on a raised ridge located.
Dorsal vertebrae: The dorsal vertebrae are mostly well preserved and comprise a series of 12 (close to a complete dorsal vertebral count of 16). The numbering system adopted here is for guidance only.
The most anterior of the preserved series is probably a first or second dorsal (d1/2; Fig. 20A–C View Figure 20 ). It retains a number of cervical morphological attributes: a low broad centrum, with a thick ventral keel and opisthocoely (and a modest convex anterior articular surface). Crucially (for positioning in the series), it has a large oval parapophysis (par) on the ventrolateral surface of the neural arch pedicel (clearly above the neurocentral suture – ncs). The transverse processes are robust and angled obliquely dorsolaterally. The prezygapophyses (prz) are separated from the midline by a shallow embayment and do not project forward; this is a standard configuration seen in cervicals ( Fig. 19A, B View Figure 19 ). The pedicels that support the postzygapophyses (poz) are elongate and therefore overlap the succeeding vertebra substantially and the neural spine (ns) is posterodorsally inclined. Unfortunately, the spine is broken so its actual length is unknown. Neural spine length may have been substantial, judged by the shape of its base, and the spine length attained by succeeding dorsals).
The next in the series is probably a third dorsal (d3; Fig. 21 View Figure 21 ). It resembles the former in that the centrum is comparatively low and broad and it retains slight opisthocoely, although its anterior face is slightly concave ( Fig. 21C View Figure 21 ). The ventral keel (k) is thick, albeit narrower than the previous example ( Fig. 20 View Figure 20 ). The parapophysis (par) is smaller and positioned higher on the neural arch pedicel above the neurocentral suture (ncs) than in the previous example. The prezygapophyses (prz) project anteriorly, are closer together on either side of the midline and the articular faces are more steeply inclined ( Fig. 21C View Figure 21 ). The transverse processes are robust, elongate, and dorsolaterally directed, terminating in a well-developed tubercular facet (dia); the anteroventral surface of the transverse process is scarred (rs) by ligaments that helped to anchor the neck of the dorsal rib. The postzygapophyses (poz) do not overlap the succeeding vertebra so extensively as in the previous example and the neural spine (ns) is little damaged, showing it to have been remarkably tall, slender, and obliquely inclined (rising to a rugose, slightly expanded, apex).
The fourth dorsal (d4; Fig. 22 View Figure 22 ) is less complete, but continues the morphological transition: the centrum is taller than wide, the ventral keel (k) is narrower ( Fig. 22B View Figure 22 ), and the anterior articular surface of the centrum is gently concave ( Fig. 22C View Figure 22 , the posterior half of the centrum is not preserved). The parapophysis is positioned higher on the pedicel, so that its upper border is now adjacent to the top edge of the prezygapophysis ( Fig. 22A View Figure 22 ) and the transverse processes are massive and ligament scarred (rs) but less upswept than in the previous example.
The seventh/eighth (d7/8) and ninth/tenth (d9/10) dorsals ( Fig. 23 View Figure 23 ) have centra of a more rectangular outline and smaller, more rounded parapophyses (par) compared with previous examples. The parapophysis (par) can also be seen to commence its lateral migration along the transverse process. These centra have a narrow keel and have shallowly concave articular surfaces [and the seventh/eighth example ( Fig. 23A View Figure 23 ) is most similar to the dorsals of the holotype NHMUK R1148 : Fig. 12 View Figure 12 ]. Judged by their shape these centra (particularly d7/8) resemble ‘keystones’ at the centre of the span of an arched dorsal series. Centrum (d9/ 10 – Fig. 23B View Figure 23 ) leans more posteriorly and has rather thicker and more prominent articular margins .
The ninth/tenth dorsal ( Fig. 23B View Figure 23 ) includes a substantial portion of its neural spine. The transverse process is less robust. The centrum is has thickened, rugose articular margins.
The most posterior dorsals (in the range d13−16: Fig. 24 View Figure 24 ) have substantially larger, almost circular, articular faces; the anterior articular face of the centrum is shallowly concave, whereas the posterior face has become more obviously opisthocoelous. The articular margins of the centra form thickened rims that are more flared than previous examples. The centra also lean posteriorly. The last preserved dorsal (probably d16) has a more regular rectangular profile ( Fig. 24 View Figure 24 C−C3) and is anteroposteriorly compressed compared with the previous two examples, and has an almost circular articular face (C1). A ventral keel (k) is present in the first two examples, but is lost in the most posterior in the series ( Fig. 24C View Figure 24 2 View Figure 2 ). The parapophyses (par) are small, forming something akin to a ‘notch’ on the leading edge of the transverse processes. The transverse processes are less robust than earlier dorsals, horizontally directed as well as twisted along their length such that the dorsal surface faces anterodorsally ( Fig. 24 View Figure 24 ).
Associated dorsal ribs: A few examples of partial dorsal ribs (NHMUK R604a) are illustrated ( Fig. 25 View Figure 25 ). The larger examples ( Fig. 25A, B View Figure 25 ) are representative of those from the anterior of the dorsal series. They have robust shafts with a well-marked longitudinal ridge (ar) running down the anterolateral margin; this probably reflects the attachment area for the intercostal ligaments and musculature. The articular rib heads [the capitulum (cap) and tuberculum (tub)] are prominent and separated by a distinct ligament-scarred neck (n – reflecting the wide separation of parapophyses and diapophyses seen in the anterior dorsal series). Two more posterior dorsal ribs ( Fig. 25C, D View Figure 25 ) are preserved and have more slender rod-shaped shafts and rib heads that are smaller and connected via a ligamentscarred ridge; this shows that the entire articular region (incorporating capitulum, tuberculum, and intervening neck) was securely fastened to its transverse process.
Caudal vertebrae: The caudals in this collection include examples from the anterior, middle, and posterior sections of the tail, each of which have their own distinctive features that are generally indicative of progressive changes in shape along the length of the tail. The anterior caudals ( Figs 26 View Figure 26 , 27 View Figure 27 ) include one with an intact neural spine of considerable height.
The most anterior caudal preserved (c2) has, when compared with others in the series, a relatively elongate centrum ( Fig. 26A View Figure 26 ), which is slightly anteriorly inclined (more so dorsally). Its anterior articular face ( Fig. 26A View Figure 26 1 View Figure 1 ) exhibits a modest convexity dorsally and shallow concavity ventrally (which is similarly reflect- ed in the morphology of the posterior face: Fig. 26A View Figure 26 2 View Figure 2 ). The centrum lacks an obvious haemal arch facet anteriorly, but a slight crease on the posteroventral rim ( Fig. 26A View Figure 26 3 View Figure 3 ) may indicate a haemapophysis (articular facet for a diminutive first haemal arch). The ventral surface of the centrum displays a pair of shallow sulci separated by a smooth midline keel and flanked lat- erally by similarly smooth ridges ( Fig. 26A View Figure 26 3 View Figure 3 ). The neural spine is broken off, but the prezygapophyses (prz) are anterodorsally directed prongs ( Fig. 26A View Figure 26 4 View Figure 4 ). The neural arch is squat and has very thick pedicels that enclose a relatively narrow neural canal. The pedicels flare laterally where they are fused to the bases of robust caudal ribs (cr), which are also sheared off.
Succeeding caudals ( Figs 26B View Figure 26 – 28 View Figure 28 ) show a graduat- ed series of changes: the centra become initially more axially compressed, the chevron facets (cf) become far more prominent on the anterior and posterior ventral rims, and the articular faces of the centrum tend to shift from an almost circular outline to more dorsoventrally elongate ( Fig. 27 View Figure 27 ). One of these caudals (?c5; Fig. 27 View Figure 27 ) is well preserved, apart from relatively minor fracturing, displaying the full development of the caudal rib and structure of the neural spine. The latter is very elongate, slightly sinuous in profile and leans posteriorly; the lower half of the spine has thickened lateral flanks that are separated by grooves from midline ridges anteriorly and posteriorly (asr, psr).
Farther behind the anterior caudals, the centra become more elongate, and have less oblique prezygapophyses ( Fig. 28 View Figure 28 ) and progressively less prominent caudal ribs. Later caudals become generally more rectangular in form and lose the prominent anterior chevron facet, as they also lose the caudal rib, which becomes reduced to a ridge on the side of the centrum. Posterior caudals ( Fig. 29 View Figure 29 ) become lower, lose the elongate neural spine, and, in proportion, their centra become more elongate and develop a hexagonal crosssection and a shallow ventral midline sulcus; these features are well displayed in NHMUK R1148 (R1632; Fig. 29B, C View Figure 29 ). The middle and posterior caudals of
| NHMUK |
Natural History Museum, London |
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.