Fig. 1 
snout. Complex articulation of premaxilla and maxilla unfused 
above subrostral notch. Small median knob at posterior end of 
conjoined nasals, cruciform in dorsal view, with anterior limb of 
cross drawn forwards into low thin median crest. Occiput deep, with 
paroccipital processes directed horizontally outwards. Basipterygoid 
processes descend far below basioccipital, diverging laterally only 
slightly. Anterior end of dentary upturned in lateral view. 6/7 pre- 
maxillary teeth; only 8 maxillary teeth preserved, but probably about 
15; 32 dentary teeth, generally smaller than those in the upper jaw, 
more than twice as numerous per unit length of jaw. Prominent bony 
wall on lingual side of all teeth. Tooth crowns flattened only slightly 
labio-lingually, lightly fluted on lingual side; anterior and posterior 
carinae finely serrated (about 7 denticles per millimetre). Tooth 
roots exceptionally long and slender. Axis small, with well devel- 
oped hyposphene. Cervical vertebrae with flat zygapophyses and 
well developed epipophyses; ends of centra not offset, no upward 
curve to neck; neurocentral sutures unfused; neural spines generally 
short, but those of basal caudals expanded into large flattened plates. 
Cervical ribs short, crocodiloid, slight overlap. Humerus relatively 
well developed; both ends broadly expanded but flattened, offset 35° 
against each other; shaft massive, almost straight. Radius stout, a 
little less than half as long as humerus. Ulna also stout, somewhat 
longer than radius, with powerful olecranon. Exceptionally large 
manual ungual phalanx, not laterally compressed, probably from 
digit I. Pubic foot not expanded. Ischium with obturator flange 
proximally continuous with anterior margin. 
Skull 
GENERAL DESCRIPTION (Fig. 1). Despite the limited amount of 
material available, several interesting observations may be made on 
the skull. It appears to have been long, at least in its anterior portion. 
Whereas in other theropods the extreme anterior end of the premax- 
illa gives rise to the steeply ascending nasal process, forming the 
anterior margin of the external naris, in Baryonyx there is no trace of 
such a process, and the anterior 170 mm of the conjoined premax- 
illae form a long low rostrum with a smoothly rounded dorsal 
surface. Even behind this rostrum there is no ascending process, the 
Baryonyx walkeri, holotype, BMNH R9951; reconstruction of skull, from left side. x 0.135. 
A.J. CHARIG AND A.C. MILNER |} 
confluent external nares appearing merely as an extensive opening 
lying well back from the tip of the rostrum and passing horizontally 
from one side of the snout to the other. The first 130 mm of the 
rostrum are expanded laterally into a spatulate ‘rosette’, not unlike 
that found in modern gavials; the first 70 mm of its lower margin are 
turned down in lateral view. Behind the ‘rosette’ the rostrum is 
remarkably narrow from side to side as seen in dorsal view. 
The maxilla fits on to the hind part of the ventral margin of th 
premaxilla by a complex articulation. The resulting effect is that th 
line of the upper tooth row, passing backwards from the front of the 
snout, first rises a little and then, at the junction of the two elements, 
curves strongly downwards and finally flattens out to run horizon- 
tally along the ventral margin of the maxilla. The net effect of this 
sigmoid curvature is that the front of the rostrum is elevated aboy 
the level of the maxillary tooth row, not depressed beneath it. This 
elevation is reflected in the shape of the upper margin of the dentary, 
the front 140 mm of which slope strongly upwards towards its 
anterior end. Nevertheless, in the region of the 5" to 6" premaxillary 
teeth, the gap between the upper and lower jaws seems to have been 
much wider than elsewhere and may be termed the subrostral notch. 
Other noteworthy general features of the skull are: 
1. The deep, narrow shape of the occiput, especially deep below the 
condyle, the basipterygoid processes greatly lengthened. 
2. The great length of the dentary, its dentigerous part very shallow. 
with well-marked Meckelian groove on the medial surface. 
3. The presence of a prominent bony wall on the lingual side of eac 
tooth row. 
4. The exceptionally high tooth count (6 premaxillary teeth on th 
left side and 7 on the right, as contrasted with a more usual count 
of 5, and 32 dentary, as contrasted with the usual 16 or so). Thi 
only other theropods known with more teeth per unit length 0 
lower jaw than in the corresponding length of upper jaw are 
Troodon(Osm6lska & Barsbold 1990) and Pelecanimimus (Pérez 
Moreno eft al. 1994), and even there the disparity is far less|~ 
extreme. 
. The much closer packing of the teeth in the dentary than in the) 
opposing part of the maxilla; as a corollary of this the dentary © 
teeth must have been generally smaller (it should be noted, 
Nn 
