' BARYONYX WALKERI 
characters, taken together, suggest that the spines in question are 
_ from the proximal caudal region of the Baryonyx vertebral column 
_ or from the otherwise unknown sacral region. 
_ The larger spine is transversely very thin and has blade-like edges; 
_ it widens towards its distal end, which may not be quite complete. In 
lateral view its dorsal profile slopes upwards from either end towards 
’ an apex that is situated somewhat behind its middle. From the centre 
of the posterior part of that profile a symmetrically rounded swelling 
| projects to a distance of about 13 mm. Towards the ventral break of 
the spine, on its posterior margin, there remains the base of the ridge 
ii that ran down towards the right postzygapophysis. Only the dorsal 
/ portion remains of the smaller spine; it is about two-thirds the linear 
dimensions of the larger, is thicker and has a more rectangular distal 
end. The posterior swelling lies more ventrally than in the larger 
‘spine, on what we presume to be the posterior profile. 
| 
Ribs 
There are numerous rib fragments, mostly of the vertebral ribs but 
some abdominals too. Many are simply broken pieces of shaft and 
do not merit description. 
VERTEBRAL. These we have arbitrarily classified, for purposes of 
description, into four groups: 
1. Cervical ribs (the left rib of the axis, plus three others, all from the 
| left side, of which only one is complete). 
2. Slender uncinate ribs (two) that we tentatively assign to the 
anteriormost part of the dorsal series (probably D1 and D2). 
3. Large, stout non-uncinate ribs (many) that clearly formed the 
greater part of the dorsal series (probably D3-D11). 
4. Significantly smaller, slightly twisted ribs that we assign to the 
posteriormost part of the dorsal series (probably D12-D14). 
(CERVICAL RIBS (Fig. 28). The complete cervical rib is of typical 
‘crocodiloid’ form and is tetraradiate in dorsal aspect. The body of 
the element is canoe-shaped; a short anterior process tapers forwards 
jand curves mediad, a longer posterior process tapers backwards and 
is virtually straight. The capitulum and tuberculum are short and 
‘stout, with a deep pneumatic pocket between their bases. This is not 
tall like the cervical ribs of Allosaurus, which are typified by a 
long, ventrally directed spine. 
ig. 28 Baryonyx walkeri, holotype, BMNH R9951; left cervical rib. A, 
lateral view; B, medial. x 0.25. 
41 
A fragment of a more posterior cervical rib bears a laterally 
directed uncinate process, with a pneumatic pocket medial to it as 
well as the pocket on the medial side of the element. The posterior 
process is broken off but appears to have been more or less straight. 
DORSAL RIBS (Fig. 29). We consider the ‘Group 2’ ribs to belong 
to the right side of D1 (first dorsal vertebra) and to the left side of D2 
(second dorsal). Each possesses a prominent, keel-like uncinate 
process on its lateral surface, just below the junction of capitulum 
and tuberculum (the first dorsal rib of Sinraptor also has a vestigial 
uncinate process). On the medial surface, a short way proximal to 
this, is a deep circular pit with sloping sides; it lies closer to the 
posterior margin than to the anterior margin. 
The best-preserved, typical (‘Group 3”) dorsal rib is of the right 
side and probably belongs to D3 (third dorsal). This robust element 
comprises a lightly curved shaft, 205 mm as preserved, that termi- 
nates dorsally in a short tuberculum; just below the tuberculum a 
relatively long capitulum diverges medially from the shaft at almost 
a right angle. (Unfortunately none of the three processes of this 
triradiate bone is complete right to its end.) The ventral profile of the 
capitulum and the medial profile of the shaft do not form a single 
smooth curve; the change in direction occurs mainly around the 
junction. The shaft tapers distally and its distal region is distinctly 
twisted so that the surface that faces anterolaterally above faces 
directly anteriorly below. The posteromedial surface of the shaft 
bears a deep, wide groove that confers an L-shaped cross-section 
upon the proximal region of the shaft but peters out distally. The 
capitulum is subtriangular in section, with a sharp dorsal margin and 
a stout, rounded ventral margin; its anterolateral surface has a 
shallow depression running centrally along its length. The medial 
surface of the tuberculum bears a prominent vertical buttress that 
disappears ventrally at the junction. 
We tried to assign the other ribs in this arbitrary grouping (D4- 
D11?) to articulation with particular vertebrae but they are too 
incomplete to be ordered reliably. 
The more posterior rib-heads (‘Group 4’, probably referable to 
D12 and D13) resemble those of other theropods in that they bear a 
long capitulum and a very short tuberculum. The tuberculum is 
reduced to a mere stub less than 20 mm long. There is no intercostal 
web of bone between the two heads. The presumed last dorsal rib, 
D14, is short (shaft length 194 mm from a point in the axil between 
the two rib-heads); its shaft is slender, flattened, convex, almost 
spatulate distally, with thin edges and a laterally directed tip. 
ABDOMINAL (GASTRALIA). Several fragments are preserved. In 
general, they are pieces of slender, gently curved, tapering shafts, 
longitudinally grooved on the dorsal surface for articulation with 
the succeeding element. A few fragments, the two longest being 
230 mm and 190 mm, have flattened, spoon-shaped, slightly 
twisted ends; these are similar to the medial ends of the same 
elements of Sinraptor (Currie & Zhao 1993), which articulate with 
the gastralia from the opposite side of the body. There are not 
enough gastralia fragments to determine the number of segments 
per side (Sinraptor has three; tyrannosaurids, fide Lambe 1917, 
have only two). 
Chevrons (haemapophyses) (Fig. 30) 
Five haemapophyses were found, four of them of very similar size 
and the fifth somewhat larger. All save one have lost varying 
amounts of their distal ends. 
The one complete haemapophysis is 190 mm long and of fairly 
typical form. The paired facets which articulated with a caudal 
