Zhen & Nicoll: Canning Basin Serratognathus bilobatus Fauna 
7 
Fig. 3. Early Floian palaeobiogeographic reconstruction of eastern Gondwana (after Nicoll et al., 1993; Webby et al., 2000; Huang et 
al., 2000). 
late Floian to Dapingian age. An et al. (1983) subdivided 
the formation into four conodont biozones (in ascending 
order): (7) Scalpellodus tarsus Biozone; (2) Serratognathus 
bilobatus Biozone; (3) Serratognathus extensus Biozone; 
and (4) Paraserratognathus paltodiformis Biozone. The 
S. bilobatus Biozone is confined to the lower part of the 
Liangjiashan Formation with a total thickness of 30 m in the 
Zhaogezhuang Section; the overlying S. extensus Biozone 
ranges through the middle part of the formation with a total 
thickness of 50 m (An et al., 1983, p. 26). 
In the Honghuayuan Formation (the coeval strata on the 
Yangtze Platform of South China), S. bilobatus is rare and 
has been reported only from the Lower Yangtze Valley (An 
& Ding, 1982, 1985). A closely related species, S. diversus, 
is dominant in the fauna. Recent studies (Zhen et al., in press 
a) of the conodonts from the Honghuayuan Formation at its 
type locality and several other sections in Guizhou resulted in 
the recognition of three conodont biozones in the Formation 
(in ascending order): Triangulodus bifidus Biozone, 
Serratognathus diversus Biozone and Prioniodus honghuay- 
uanensis Biozone. In the type section of the Honghuayuan 
Formation, S. diversus is confined to an interval of 13.5 m in 
the middle part of the Formation which is correlated to the 
upper P. proteus Biozone of the Balto-Scandian succession 
(Zhen, 2007, Zhen et al. in press a). 
When correlating the conodont fauna from the Emanuel 
Formation and the lower Gap Creek Formation with well- 
studied Balto-Scandian and North America Mid-continent 
conodont successions, McTavish (1973, p. 31) was puzzled 
by the fact that Balto-Scandian Lower Ordovician succes¬ 
sions were condensed, while North America Mid-continent 
successions, although with “comparable thickness to the 
Emanuel Formation” had faunas “of limited value for precise 
age determination”. At the time, he did not attribute these 
faunal differences and difficulties in correlation to either 
ecological or biogeographical reasons. It is now understood 
that distribution of conodont animals was largely controlled 
by the water temperature and the water depth of their habitats 
(see Zhen & Percival, 2003). Higher resolution of the faunal 
correlation can only be achieved by comparing faunas from 
the same biogeographical province and Domain or at least 
from the same realm, otherwise ecological and biogeo¬ 
graphical overprints should be removed or discounted when 
comparing faunas from different biogeographical settings. 
A restricted distribution of Serratognathus in eastern 
Gondwana (Fig. 3) strongly supports the concept that the 
so-called “Australasian Province” became evident in the 
latest Tremadocian and early Floian, and persisted through 
