336 
C.J. Burrow 
Figure 5 Single tooth and tooth-like cones from the Trundle beds, central New South Wales. A, single tooth 
MMMC02277; B, tooth-like cone type I MMMC02252; C, tooth-like cone type II MMMC02268. Scale bars = 
0.1 mm; A is an SEM photograph of an uncoated specimen. 
latter appear to consist of a row of tooth-like 
processes interspersed with smaller, irregularly 
arranged processes/cusplets. The arrangement is 
reminiscent of that of the main cusp row of the 
dentigerous jaw bones. 
The other six cones of this type are of a similar 
size and shape. 
Dentition cone, type II (Figure 5C) 
This cone (MMMC02268) is more robust than the 
previous type, with thicker walls and oblique 
denticles scattered over the cone surface. The main 
cone body is formed of bone, while the denticles 
are shiny and probably dentinous. 
The other six cones range from 0.8 to 2.0 mm 
high. 
Class Acanthodii incertae sedis 
Acanthodii gen. et sp. indet. 
Asymmetrical multiple tooth whorl (Figure 4D,E) 
This incomplete element (MMMC02250) is 0.9 
mm long and 0.4 mm wide centrally, and has an 
arched base, bearing radiating whorls of teeth. The 
crown comprises two apparently complete whorls, 
each with at least six teeth or tooth rows. The teeth 
increase gradually in height from less than 0.1 mm 
at the front to as much as 0.6 mm at the rear. The 
largest tooth row of the best-developed whorl has 
the largest central cusp, which has two side cusps 
about 0.15 mm high. The cusps are sub-circular in 
parabasal section. Side cusps are poorly developed 
or absent on most teeth. Adjacent to the anterior 
section of this whorl are two broken teeth which 
appear to be part of a third whorl. 
Denticulated plate with tooth whorl (Figure 4F) 
This asymmetrical element (MMMC02251) is 1.1 
mm long and 0.3 mm wide. The posterior portion 
has a similar form to that of typical tooth whorls - 
i.e., a concave base, and tooth rows with a large 
central cusp and smaller side cusps. The whorl is 
skewed relative to the anterior base plate, which is 
elongated and flat. Its crown has worn, irregularly 
shaped cusps or tubercles. The thin lateral edges of 
the plate are also tuberculated. 
The other six plates are of a similar size and 
pattern; three have a tooth whorl skewed right 
relative to the plane of tire plate, and three are 
skewed to the left (if all were originally positioned 
in either upper or lower jaws). Plate MMMC02205 
(Figure 6D) was sectioned longitudinally; 
unfortunately, preservation was poor, and most 
histological detail is obscure (Figure 6E). 
DISCUSSION 
Early ischnacanthids possessed a wide range of 
dental elements, as evidenced by those fish that 
have been found as articulated specimens, and by 
the detailed studies of microremains by Gross (e.g., 
1957,1967,1971b). In the following paragraphs, the 
new specimens are compared with those 
previously described, to determine the possible 
positions and affinities of the dental elements. 
