The Yule Island Fauna and the Origin of Tropical Northern Australian Echinoid (Echinodermata) Faunas

Abstract

Systematic description of the rich Lower Pliocene echinoid fauna from Yule Island, Papua New Guinea, and recently available palaeogeographic data from onshore Papua, the Gulf of Papua and Torres Strait have provided new insights into the origins of the extant tropical northern Australian echinoid fauna. Previous studies of echinoderm origins, hindered by a lack of fossil evidence, concluded that tropical northern Australian echinoderms were derived predominantly by Recent migrations from East Indian and West Pacific stocks. However, 47 per cent of species from the Yule Island fauna are extant in northern Australian waters, indicating that present faunistic patterns were to a large extent, in-place by at least the Lower Pliocene. Palaeogeographic evidence supports the earlier observations of H. Barraclough Fell, that migration of echinoid stock into (and out of) eastern New Guinea and tropical northern Australia probably occurred during the Lower to Middle Miocene, when widespread tropical to sub-tropical reef development occurred across a 5600 km belt from SE Asia through New Guinea and into the SW Pacific as far as Fiji. This favourable pathway for exchange between echinoid stocks disappeared during the Upper Miocene, when the onset of tectonic instability throughout the region, and the establishment of a discontinuous volcanic arc, resulted in influx of terrigenous sediments and may have caused the death of the reef complex. This pattern of sedimentation has persisted to the present.