Devonian macrovertebrate assemblages and biogeography of East Gondwana (Australasia, Antarctica)

Abstract

The biogeographic significance of Devonian macrovertebrate assemblages from East Gondwana is reviewed, with updates incorporating recent discoveries including new placoderms (antiarchs, groenlandaspid arthrodires, phyllolepids), sarcopterygians (mandageriine tristichopterids, actinistians, rhizodontids), and actinopterygians. Key taxa are illustrated by new specimens. Empirical patterns indicating range expansion from the area of origin for particular groups are analysed and discussed. The almost complete absence of armoured agnathans from the Devonian of Australia remains one of the most significant differences to Northern Hemisphere deposits, implying an isolating mechanism (oceanic or climatic barrier) between Gondwana and Laurussia during the Silurian-Early Devonian. Increasing faunal exchange with Asia during the Devonian may have been initiated with Pragian-Emsian faunal turnovers in South Chinese assemblages. A Gondwanan pattern in Devonian vertebrates persists into the Frasnian, until the Great Devonian Interchange at or near the Frasnian-Famennian boundary establishes strong Laurussian affinities in the early Famennian, when phyllolepid placoderms first appear in the Northern Hemisphere. New data documented on Early Devonian phyllolepids from Gondwana indicate an extended biostratigraphic range, and a diversity maximum in the Givetian-Frasnian. A late Famennian faunal exchange with Asia is suggested by sinolepid antiarchs, but requires corroboration from other fish groups, with conflicting Laurussian affinities indicated by new sarcopterygian and acanthodian data. An alternative explanation of physiological adaptation within sinolepids is discussed, as is the key question of tetrapod origins, for which the only Devonian examples outside Laurussia occur in Australia and China. The vertebrate biogeographic patterns are completely contrary to palaeogeographic reconstructions based on palaeomagnetic evidence. Show more