Biostratigraphy of Devonian microvertebrates 
427 
Remarks 
Few Palaeozoic chondrichthyan teeth figured in 
the literature are single-cusped, a condition 
considered by Zangerl (1981) to be the least 
specialised morphological type. One monocuspid 
form, however, is Cobelodus aculeatus (Cope) 
described by Zangerl and Case (1976) from the Late 
Carboniferous of North America; teeth from the 
upper dentition (Zangerl and Case 1976, figure 16; 
Zangerl 1981, figure 8E) are similar to the Broken 
River specimens in the single conical cusp being 
attached to a bulbous base, but differ in the cusp 
being longer and finely striated. 
Figured teeth of Antarctilamna prisca and 
"Xenacanthus" sp. (the latter recently referred to a 
new genus Portalodus - Long and Young 1995) 
from the late Givetian or early Frasnian Aztec 
Siltstone in Antarctica (Young 1982, text-figure 3, 
plate 89, figures 1-4) bear a slight resemblance to 
the Broken River specimens. Histologically, the 
Broken River specimens have a similar structure to 
that described by Young (1982) for Antarctilamna 
teeth. However, the Antarctic teeth differ in being 
diplodont, in having the cusps curved, partly 
striated, perhaps with an accentuated striation or 
flattened side close to the base to form a cutting 
edge, and in the root being concave with a torus on 
the lingual side (Young 1982). 
Description 
The conical teeth are set centrally or towards one 
edge of a bulbous, subspherical base. One 
specimen (Figure 4J) from SD210/104 m in middle 
varcas Zone has a small second cusp; both cusps 
are broken distally. All other specimens are single- 
cusped. The cusps are about 0.4-0.5 mm long, 
smooth and uncurved, with a circular cross-section 
and blunt tip. Apart from the two-cusped 
specimen, the teeth are similar in size and shape; 
this lack of variation is common in Devonian 
elasmobranchs (Young 1982). The base has a ring 
of small holes close to the base of the tooth (Figure 
4K). In some specimens, the central part of the base 
contains a spherical pulp cavity that extends a 
short distance into the cusp in a broad conical 
shape; in others, the base has no foramina or 
cavities. 
Discussion 
The samples containing these chondrichthyan 
teeth have also yielded numerous disarticulated 
scales, assigned to three new chondrichthyan form 
genera: Gondwanalepis, Notiolepis and Aussilepis, 
with respective ranges of kockelianus to younger 
than varcns, mid-ensensis to younger than varcus, 
and ensensis to younger than varcus (De Pomeroy 
1994). As the stratigraphic ranges of these scales 
and that of the 61 teeth are similar, it is possible 
the teeth are from one of these genera. 
Class Elasmobranchiomorphi 
Subclass Placodermi 
Order Arthrodira Gross, 1932 
Arthrodire indet. 
Figures 6G, H, J 
Material 
One possible arthrodire infragnathal (lower 
dermal jaw bone) (QMF 31852) and one scale (QMF 
31853). 
Localities 
QMF 31852: SD198/67.6 m; Lomandra Limestone. 
QMF 31853: SD170/200 m; Bracteata Formation. 
Stratigraphic levels 
QMF 31852: Givetian (varcus Zone). 
QMF 31853: Emsian ( serotinus Zone). 
Remarks 
This scale (QMF 31853) is dissimilar to the 
asterolepidoid antiarch Wurungulepis (see Young 
1990, figure 13), the only other placoderm scale 
type described from this area. The ornament 
resembles that on scales of a buchanosteid 
arthrodire from Taemas (specimen CPC 16965, 
held at AGSO, Canberra). In the Broken River 
specimen the radiating ridges extend to the top of 
the tubercles, in contrast to the tubercles of CPC 
16965, which are smooth in the centre and ridged 
only around the edges, but this scale type also 
occurs at Taemas (e.g. 'Ohioaspis tumulosa' Giffin 
1980, figure 3). Similar "buchanosteid"-type body 
scales are illustrated from the Lochkovian ( delta 
Zone) of Nevada (Turner and Murphy 1988:962, 
figures 2.8-2.12). 
Description 
Fragment QMF 31852 (Figures 6G, H) measures 
almost 2mm long and just over 1mm high. Four 
spatulate denticles are ankylosed to the upper 
(dorsal) surface, with no obvious delineation 
between the material of the denticles and that of 
the bone. Two small foramina, probably for the 
passage of nerves or vessels (arrows in Figure 6H), 
are situated near the anterior margin of the bone. 
The ventral surface has a deep longitudinal groove, 
which would contain the meckelian cartilage if 
interpretation as an arthrodire infragnathal is 
correct. This groove starts a short way back from 
the blunt anterior tip of the bone, immediately 
posterior to a foramen (lower arrow in Figure 6H). 
The sides of this deep groove are composed of thin 
bone, in contrast to the more robust structure of 
the dorsal denticulate region and the solid anterior 
tip. One side extends further ventrally than the 
other (Figure 6G). Along one lateral surface a 
