292 
J.A. Long, G.C. Young 
Localities and horizon 
WAM 90.2.37, 92.3.68, 92.4.5: Cook Mountains, at 
"Gorgon's Head", near Mt Hughes, in the upper 20 
m of the Aztec Siltstone, associated with a diverse 
fauna including phyllolepid placoderm remains, 
Pambulaspis, Bothriolepis, Groenlandaspis, 
osteolepiform scales, Gyracanthides spines, and a 
lungfish toothplate resembling Eoctenodus sp. 
(Woolfe et al., 1990). WAM 92.4.3, 92.2.4, 92.4.6: Mt 
Ritchie, middle horizon, about 120 m from base of 
section 24 of Young, (1988); WAM 94.2.2: Lashly 
Range (LA 2 site, third outcrop of Aztec Siltstone 
south of L2, Mt Crean main section, lower horizon). 
Remarks 
These specimens resemble the type material in 
having large divergent main cusps ornamented 
with 4-6 sparse ridges, and 1 to 5 small median 
cusps. However some come from a much higher 
horizon than the type material (which occurs in the 
lowest Aztec biozones of Youngl988). Until more 
material is found on which morphological 
differences might be demonstrated, we 
provisionally consider the specimens as close to the 
type species of Antarctilamna. 
Description 
These specimens vary in size as measured across 
Figure 3 Antarctilamna teeth. A, WAM 94.2.2 from the 
Lashly Range (site LA-2) in labial view. B, 
WAM 92.3..68, from "Gorgons' Head", Cook 
Mountains, in labial view. C, WAM 2.3.62, 
from the top horizon at Mt. Ritchie, labial 
view. All x 8. 
the base, all falling within the range of 1-4 mm 
described in the holotype. As noted above they 
resemble the type material in having two divergent 
main cusps, ornamented with 3-6 sparse ridges 
which curve up from the base, WAM 90.2.37, 
preserved in labial view, shows an impression 
where a single median cusp was present. The labial 
surface is somewhat weathered but still shows 
evidence for 3-4 weak striae on the main cusps. 
WAM 92.3.68 (Figures 3B,4C) has a median cusp 
slightly larger than the two lateral cusplets, all of 
which sit between the two main divergent cusps. 
This specimen comes from the youngest horizon at 
the top of the Aztec Siltstone at Gorgon's Head 
(Mt Hughes) and shows the base being more sub- 
rectangular in form rather than having a rounded 
lingual margin as shown in Young's reconstructed 
specimen (1982, text-figure 3 C). The striations 
extend onto the intermediate cusps (Figure 3C, 4). 
Between the two main cusps on WAM 94.2.2 
(Figure 3A) there are two pairs of small median 
cusps lateral to a slightly larger central cusp that 
has broken off at its base. Thus there would have 
been five median cusps between the two divergent 
main cusps. The striae on this specimen number up 
to 7 on each main cusp and even the median 
cusplets have striae developed. In cross-section the 
cusps and intermediate cusplets are weakly 
compressed, almost round at the base become 
flatter near the apex of each cusp. The lateral and 
mesial edges have a sharp cutting edge running 
half way down the sides of each main cusp. 
All the known Antarctilamna teeth have three or 
more small intermediate cusps, and of these the 
central cusp is slightly larger than the two or four 
lateral cusps, as was observed in the type material 
(Young 1982: 824, plate 87, figure 1; also see 
Appendix, Figure 13). In these specimens the 
number of intermediate cusps varied between two 
and three, but this was a much larger sample 
(about 65 teeth from the holotype). It is possible, 
however, that all Antarctilamna teeth from these 
higher horizons have three intermediate cusps, but 
this needs to be substantiated with a larger sample. 
Hampe (1993) indicated that a range of tooth 
abnormalities occurs in bicuspid xenacanth teeth, 
including the appearance of additional median 
cusplets. In the holotype of Antarctilamna prisca it 
was suggested that striations may be restricted to 
the outer surface of the crown (Young 1982: 824), 
and this observation is confirmed by the new 
specimens. WAM 92.3.62 (Figures 3C, 4A, B) shows 
a larger ventral foramen surrounded by some 
smaller foramina opening through the base, as in 
Phoebodus (e.g., P. gothicus; Gross 1973: plate 34, 
figure 15b; Ginter 1990), but not previously noted 
by Young (1982) in the type material. A slight 
protuberance on the labial margin (Figure 4A, B) is 
the basal tubercle corresponding to that developed 
