Biostratigraphy of Devonian microvertebrates 
431 
environments situated on the northeastern margin 
of Gondwana during the Devonian (Scotese and 
McKerrovv 1990), and so could be expected to have 
similar faunas. Indeed, preliminary studies of 
microvertebrate faunas from Buchan and Taemas 
reveal cheiracanthoid and nostolepid scales and 
onychodontid teeth, not unlike those found at 
Broken River. 
Order Ptyctodontida Gross, 1932 
Family Ptyctodontidae Woodward, 1891 
?Ptyctodontid indet. 
Figures 6B, O, P 
Material 
One probable supragnathal (upper toothplate) 
fragment (QMF 31847; Figure 6B) and one quadrate 
(QMF 31857; Figures 60, P). 
Localities 
QMF 31847: SD111/29 m; Dosey Limestone. 
QMF 31857: SD15/145.6 m; Papilio Formation. 
Stratigraphic levels 
QMF 31847: Eifelian (cnsensis Zone). 
QMF 31857: Givetian (Middle varcus Zone). 
Remarks 
Specimen QMF 31847 (supragnathal) is placed 
tentatively in the family Ptyctodontidae as is has a 
wedge-shaped cross-section similar to Ctenurella 
gardineri (and as reported by Watson 1938 in 
Rhamphodopsis ) and the anteroventral comer of the 
biting edge extended into a slight, rounded beak as 
in C. gardineri and Campbellodus decipiens (Miles and 
Young 1977). The Broken River specimen also 
resembles figured Rhynchodus-type supragnathals 
from the Frasnian and Famennian of Iran (Lelievre 
et al. 1981: figure 23A,B). The broken dorsal edge 
of the specimen prevents observing the presence of 
an anterior dorsal process, found in Ctenurella, 
Campbellodus and Rhatnphodopsis trispinauts (Miles 
1967; Miles and Young 1977). The mesial surface 
just behind the anterior margin lacks the grooves 
common in ptyctodontids (Miles and Young 1977). 
Specimen QMF 31857 (quadrate) is also placed 
tentatively in this family as it is similar to a 
quadrate of C. gardineri (Miles and Young 1977) 
recovered from the Frasnian Gogo Formation. This 
specimen differs from C. gardineri, however, in 
lacking the lateral and mesial ridges adjacent to the 
main shaft of the bone that articulated with the 
upper toothplate, and in possessing an articular 
process (arrow in Figure 6P) at the posteroventral 
end. Indeed, any placoderm group without dermal 
bones in the cheek (e.g. phyllolepids) could have a 
quadrate similar to this specimen (G.C. Young, 
pers. comm.). 
Description 
QMF 31847: The 2 mm long fragment is 
incomplete dorsally and posteriorly, with open 
spongy bone visible along the dorsal margin, the 
anterior margin is extended ventrally into a slight, 
rounded beak. The surface is unornamented and 
shows no evidence of lamellae or grooves. 
QMF 31857: This fragment is about 2.5 mm long. 
The open, flared anterior end (Figure 60) is hollow 
for about half the total length of the fragment. The 
opposite, posteroventral end has a solid, rounded 
condyle, interpreted as the articulating surface 
with the articular bone of the mandibular joint, and 
a separate shallow, hollow cylindrical process 
(arrow in Figure 6P). 
Discussion 
Quadrates from several arthrodires from the 
Frasnian Gogo Formation have been figured and 
described; none resemble the Broken River 
specimen. The quadrate of Catnuropiscis is co¬ 
ossified with the palatoquadrate (Dennis and Miles 
1979a), and that of Rolfosteus and Kendrickichthys 
with the postsuborbital plate (Dennis and Miles 
1979b, 1980). In Incisoscutum and Latocamurus the 
quadrate is a separate, elongate bone (Dennis and 
Miles 1981; Long 1988). 
Ptyctodontids had a pair of upper and lower 
toothplates that operated by crushing, grinding or 
shearing (Denison 1978). Ctenurella, Campbellodus 
and Rhamphodopsis have a shearing edge on the 
lingual surface (Miles 1967; Miles and Young 1977), 
whereas the biting areas of Ptyctodus and 
Palaeomyltis bear tritors and rounded tritoral cusps, 
respectively (0rvig 1960). The family has been 
reported from the Early Devonian of Iran and the 
Soviet Arctic, the Emsian Taemas-Buchan fauna of 
southeastern Australia, and the Eifelian to 
Famennian of North America, Europe, Scotland, 
former USSR, Iran, Libya and Australia (Hussakof 
and Bryant 1918; 0rvig 1960; Miles 1967; Miles and 
Young 1977; Denison 1978; Lelievre et al. 1981, 
1988). 
Placoderm indet. 
Figures 61, K, L 
Material 
Three scales (QMF 31854,5 and one other). 
Localities 
SD128/137 m and SD238/227 m; Papilio 
Formation. 
Stratigraphic level 
Givetian ( varcus Zone). 
Description 
The figured scales measure 1.1-1.2 mm along the 
