Is the New Guinea Emerald Tree Monitor Lizard (Varanus prasinus) Native to Mainland Australia?

We summarize and evaluate anecdotal information and observations about the potential occurrence of the New Guinea emerald tree monitor lizard, Varanus prasinus (Schlegel, 1839), on mainland Australia. Several independent but unconfirmed reports about sightings of large green lizards in the rainforests on Cape York Peninsula have been published in the last 40 years, but still no photographs or voucher specimens exist. The closest confirmed occurrence of V. prasinus to mainland Australia is on Moa (also known as Mua or Banks) Island, one of the islands in the Torres Strait that separates New Guinea from Australia. The shallow tropical waters of the Sahul Shelf  surrounding these small islands were dry land during Pleistocene glacial periods and facilitated faunal exchanges between both huge landmasses in the past. Consequently, a natural occurrence of V. prasinus on Cape York, together with the endemic Varanus keithhornei (Wells and Wellington, 1985), the canopy goanna, seems plausible. Likewise, a possible polymorphism in the color pattern of the latter species as a putative result of repeated introgression and/or hybridisation events as source for the sightings of green tree monitors deserves further investigations. Therefore, we encourage future field work in this remote area to finally answer the question if the New Guinea emerald tree monitor is native to mainland Australia.