Middle Palaeozoic microvertebrate assemblages and biogeography of East Gondwana (Australasia, Antarctica)

Abstract

Silurian vertebrate remains are rare in the Australasian region, mostly lacking from the end Ordovician to the mid-Ludlow presumably because of the purported Gondwana Ice Age. Thelodont, placoderm, acanthodian, ?stem actinopterygian, and probable chondrichthyan remains are known from eastern and western Australia and Irian Jaya. Of significance are the links between eastern Australia and China, with sinacanthid spines known only in these regions, and both having porosiform, but not punctatiform, poracanthodid acanthodians, while Western Australia, Iran and possibly Irian Jaya have similar thelodonts, all from shallow marine to evaporitic settings. Earliest Devonian (Lochkovian) vertebrate microfossils include placoderm taxa with circumArctic and Bohemian affinities, but post-Lochkovian marine assemblages comprise mainly endemic forms of turiniid thelodonts, placoderms, acanthodians, chondrichthyans, and sarcopterygians. Most of the Early Devonian marine assemblages from eastern Australia indicate tropical–subtropical depositional environments. From the Middle–Late Devonian, notable index taxa include Phoebodus spp. After the Frasnian-Famennian events, turiniids finally disappear in the Australian record, placoderms also become absent by the end of the period, acanthodians are increasingly dominated by acanthodiforms, and chondrichthyan and actinopterygian diversity increases. For the Carboniferous, vertebrate occurrences are early to mid-Mississippian, disappearing in the early Pennsylvanian in marine and non-marine environments. During the time span of IGCP 491, data on previously poorly known and many new taxa represented only by isolated remains have been analysed, and a wealth of new acanthodian taxa, a new Early Carboniferous tetrapod Ossinodus pueri, and several sarcopterygian taxa have been fully described.