42 
Fig. 29 Baryonyx walkeri, holotype, BMNH R9951; isolated dorsal ribs; A, B, anterior; C, D, mid-dorsals; E, F, posterior. x 0.17. 
vertebra are united by a bridge, producing a saddle-shaped proximal 
end. The paired anterior processes found in Dilophosaurus and 
Allosaurus are altogether absent here, in which respect Baryonyx 
resembles Ceratosaurus. The distal portion of the bone, beyond the 
point of union of the two sides, is transversely flattened and ex- 
panded into a blade-like structure with a straight anteroventral 
margin and a concave posterodorsal margin. 
Sternum (Fig. 31C) 
A fragile plate of bone, in some places no more than | mm thick, has 
broken edges nearly everywhere. However, it is strongly ridged like 
a tile from the ridge of a pitched roof, with two smooth surfaces lying 
at an angle of some 40° to one another, suggesting that the fragment 
is a single median element with a median angulation. At what 
appears to be its anterior end the bone is considerably thickened; 
each half has a convexly curved anterior termination, and between 
the two is a median embayment. Part of the right-hand edge is a true 
margin which runs diagonally to the midline, thereby indicating that 
the bone originally widened rapidly towards its thickened posterior 
end. 
Fig. 30 Baryonyx walkeri, holotype, BMNH R9951; isolated 
haemapophysis. A, left lateral; B, posterior. x 0.25. 
A.J. CHARIG AND A.C. MILNER 
Sternal elements have seldom been reported in theropods. In 
Sinraptor (Currie & Zhao 1993) a fragment of a broad plate with a! 
median ventral ridge was found. Some other theropods, e.g. 
Carnotaurus (Bonaparte et al. 1990) and Albertosaurus (Lambe 
1917), have paired, unfused sternals; this could be related to imma- 
turity. The fusion of paired plates into a single median element in’ 
Baryonyx (despite the lack of co-ossification of the various compo- 
nents of the skull and vertebrae) might suggest the contrary, that the 
animal was fairly mature. 
Pectoral girdle 
SCAPULA (Fig. 31A). Both scapulae are preserved incomplete. 
Whereas the base of the left scapula lacks only part of the acromion 
process, the base of the right scapula is missing entirely, being }) 
broken off transversely a short distance above the glenoid. Both) 
scapulae also lack the dorsal end of the blade, the right seeming to be 
almost complete distally but its partner rather less so. The following| 
description is based on both. 
The scapula is typically theropod in most respects, somewhat 
curved in anterior or posterior view to fit the shape of the body. The : 
blade is long and strap-like with subparallel sides, although its distal} 
(i.e. dorsal) end is slightly expanded. It is robustly constructed, with | 
rounded edges; the anterior edge is a little thicker than the posterior. 
The blade thins somewhat dorsally and the edges become sharper, 
more truly blade-like. 
Ventrally the blade expands greatly; it expands anteriorly into they 
thin (and broken off) acromion process, while the posterior edge! 
thickens gradually in a mediolateral direction. At the same time it 
expands posteriorly, terminating in the backwardly directed scapu- 
lar portion of the glenoid fossa and, adjacent thereto, in the ventrally! 
directed facet for the coracoid. The glenoid facet is shaped like a) 
deep inverted U, while the coracoid facet is broad and robust beneath) 
the glenoid but tapers anteriorly towards the acromion process. A! 
straight, distinct ridge is formed where these two facets meet at an) 
angle of about 45°. . 
In lateral view the ventral margin of the scapula, where it sutures 
with the coracoid, forms a shallow single zigzag which is reflected}, 
exactly in the corresponding dorsal margin of the coracoid (see) ; 
below). 
