Fig. 16 Baryonyx walkeri, holotype, BMNH R9951; right surangular fragment. A, lateral (labial) view; B, medial (lingual). x 0.5. 
into a longitudinal flange with a deep ridged groove above it, 
presumably for articulation with the prearticular. Farther forwards, 
however, in the region of the angle in the ventral margin, this flange- 
and-groove becomes transformed into a simple rounded ridge with 
an elongated shallow depression between it and the angle; still 
farther forwards the ventral margin becomes much narrower. 
The lateral surface of the angular, at the posterior end of the 
fragment as preserved and just beneath its dorsal margin (i.e. the 
lower border of the external mandibular fenestra) is depressed below 
the general level of the surface. The edge of this depression, demar- 
cating it from the general level, runs more or less parallel to the lower 
margin of the bone in a gentle curve; the depressed area is therefore 
much thinner than the rest of the blade. 
CORONOID (Figs 17C,D). A small, roughly triangular bone, seem- 
ingly complete, is presumed to be the right coronoid. The dorsal 
edge is the longest; the weakly concave posteroventral edge is 
slightly shorter; the undulating anteroventral edge is the shortest of 
the three. Both lateral and medial surfaces are generally flat A 
broad, laterally facing facet for the prearticular runs along the 
anteroventral edge. Two somewhat similar facets for the surangular 
run along the posterior two-thirds of the dorsal edge, with a narrow 
ridge between them; one faces obliquely laterally and the other, 
rather narrower, obliquely medially. The concave posteroventral 
edge is the anterodorsal margin of the adductor fossa. 
Dentition (Figs 18, 19) 
Most of the teeth preserved are in isolation; a few remain in the 
premaxilla and maxilla, but none (except for a few tiny replacing 
teeth) remains in the dentary. They have a general theropod appear- 
ance, being simple recurved cones, somewhat flattened labiolingually, 
A.J. CHARIG AND A.C. MILNER 
with serrated mesial and distal carinae. At the same time, however, 
they show a number of characteristic peculiarities: 
1. They have very long roots, tapering significantly towards th 
apex, so that each tooth as a whole is unusually long and slender, 
This character creates the false impression that the isolated tee 
of Baryonyx are less recurved than those of most other carniy 
orous archosaurs. However, the larger tooth crowns are slightly 
less recurved than the smaller ones. 
2. They show only slight labiolingual flattening, much less than i 
the more blade-like teeth of nearly all other theropods. 
3. The carinae are strongly developed, forming, along both mesial 
and distal edges of the tooth, a distinct ridge with its surface 
demarcated from the general surface of the crown by a more OI 
less straight line. The carinae run the full length of the crown. 
4. Both mesial and distal carinae bear extremely fine denticles. 
approximately 7 to the millimetre; the only other theropods wi 
comparable denticle count are Saurornithoides, with 7-8 per m 
(Sues 1978), and Ricardoestesia, with about 5 per mm (Currie éi 
al. 1990). The denticles (Fig. 19) are tall, narrow and sub-parallel 
sided, with flat or slightly fluted tops (probably due to wear) an 
relatively uniform in size, irrespective of the size of the tooth, 
This condition differs markedly from that shown by theropods ir 
general, where the basal length of the tooth denticles increase 
with increasing tooth size in linear fashion (Farlow et al. 1991). 
Spinosaurus (Stromer 1915), Angaturama (Kellner & Campo 
1996) and /rritator (Martill et al. 1996) lack serrations alto 
gether. 
5. The lingual surfaces of the crowns are longitudinally fluted (1.€.} jy 
they bear about 6-8 ridges). 
6. The enamel on both surfaces has a finely granular appearance. 
ti 
