306 
J.A. Long, G.C. Young 
not provided. Omalodus bryanti Ginter and Ivanov 
1992, is recorded from the late Givetian of the 
Kuznetsk Basin, but the original material of Wells 
(1944) came from the same locality as Ph. floweri 
(Kiddeville bone-bed, lower part of Boyle 
Limestone), and this was also regarded by Wells 
(1944) as Givetian in age. 
Biogeography 
The diversity of middle Palaeozoic 
chondrichthyans from the Gondwana continents 
resulting from new discoveries over the last 15 
years indicates that a substantial part of their fossil 
record is not represented in the well-studied 
Palaeozoic successions of the Northern 
Hemisphere. The only possible chondrichthyans 
(based on teeth) from the Early Devonian of the 
Euramerican or Asian terranes is material of 
Doliodus problematicus from the Emsian of 
Campbelltown, New Brunswick, Canada. This 
material, now housed in the Natural History 
Museum, London, was originally described by 
Woodward (1892) as acanthodian teeth, and has 
been re-examined by one of us (JAL). Some teeth 
(e.g., BMNH 7076) show a well-developed root 
system with vascular canals present, a 
characteristic of chondrichthyan teeth. Despite this, 
most of the record of Early Devonian sharks is 
from Gondwanan or neighbouring Gondwanan 
terranes, suggestive of a Gondwana origin for the 
chondrichthyans (exclusive of identifications based 
on scales alone). 
Apart from the diplodont teeth of several taxa in 
the Aztec fauna dealt with above, similar teeth are 
also known from southern Africa (Bokkeveld 
Formation, upper Middle Devonian, Oelofson 
1981), and South America and various parts of the 
Middle East have yielded similar fin-spines (but 
apart from Saudi Arabia, no teeth as yet). All of 
these areas are thought to have been part of 
Palaeozoic Gondwana, and a synthesis of these 
occurrences is given in Lelievre et al. (1993). 
Previous biostratigraphic and biogeographic 
assessment of the Antarctic Aztec assemblage led 
to the hypothesis of Gondwana origin for the 
xenacanth clade, and subsequent dispersal into the 
northern hemisphere (Young 1989a, 1990). This 
was in accord with evidence from a range of taxa, 
both invertebrate and vertebrate, indicating a biotic 
dispersal episode, perhaps related to changes in 
global palaeogeography (e.g.. Young 1981,1987). 
ACKNOWLEDGEMENTS 
Fieldwork in Antarctica over the 1991/92 season 
was funded through ASAC grant #136 to JAL, who 
thanks the Director and Trustees of the Western 
Australian Museum for their support, and field 
colleagues Margaret Bradshaw, Fraka Harmsen 
and Brian Staite, for their assistance and support 
during the field trip. GCY acknowledges the 
assistance of Drs A. Ritchie and P.J. Barrett for his 
participation in the 1970-71 VUWAE 15 expedition 
under the New Zealand Antarctic Research 
Program. Field and logistic support was provided 
by the 197071 staff at Scott Base, US Navy 
Squadron VXE6, and other members of the 
VUWAE 15 team (R. Askin, P. Barrett, R. Grapes, 
B. Kohn, J. McPherson, and D. Reid). GCY also 
acknowledges a travel grant from the 
Transantarctic Association. Discussions and 
unpublished information on xenacanth sharks have 
been provided by H.P. Schultze, J. Zidek, O. 
Hampe, J. Maisey, and others. Dr Alex Ritchie 
(Australian Museum) allowed access to collections, 
and discussed various aspects of the Aztec fauna. 
Both authors acknowledge financial and other 
support from IGCP Project 328 (Palaeozoic 
microvertebrates), and extensive discussions with 
S. Turner and M. Ginter on fossil shark teeth. For 
the excellent photography we thank Kris Brimmell 
(WAM specimens) and R.W. Brown and H.M. 
Doyle (AMF and CPC specimens). Kate Trinajstic 
is thanked for her help editing the MS. 
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