A new diminutive species of Varanus from the Dampier Peninsular, western Kimberley region, Western Australia

Abstract

Varanus lizards in Australia are moderately diverse and include a radiation of smallbodied species that occur in arid or tropical environments. Varanus brevicauda is the smallest species, with an elongate body and short prehensile tail and is associated with spinifex clumps in arid environments. Recently collected unusual specimens at the north-western edge of the range of V. brevicauda on the Dampier Peninsula, Western Australia, had an even more elongate body and also co-occurred with typical V. brevicauda. This led us to conduct a morphological and molecular genetic systematic appraisal of the two morphotypes. We found that the more elongate specimens were highly divergent genetically from both typical V. brevicauda and another related species, V. eremius, with the three lineages forming a polytomy. Morphologically, the elongate specimens are most similar to V. brevicauda, but possess a more elongate body, less robust head and limbs, distinctive scales on the front of the arms that are large, squarish and lacking surrounding granules and a plainer pattern and colouration. The co-occurrence of both forms on the Dampier Peninsula in combination with the extent and pattern of genetic divergence and presence of key morphologically diagnostic traits unequivocally demonstrates that more elongate form is a new species, which we describe here. The new species may be of conservation concern owing to the small range of the only known specimens and development proposals in the area.