Morphological variation between populations of the Brush-tailed Tree Rat Conilurus penicillatus in northern Australia and New Guinea

Variation in external and cranial morphology was studied in Conilurus penicillatus from six geographical regions. Sexual dimorphism (males being larger than females) in body weight and pes length was noted. Animals from Bathurst and Melville Is were distinct from other regions in that they had shorter ears, pes and head and body lengths, and dark ventral pelage. The two specimens from New Guinea had large bodies and pes, and short ears when compared with Australian animals, but incomplete data and small sample sizes precluded inclusion in the discriminant function analyses of external features. All animals from the Cobourg Peninsula, eastern Northern Territory and islands in the Gulf of Carpentaria were black-tailed. Up to 42% of animals from other populations had white tail tips. Analysis of cranial variables showed that there was a considerable degree of distinctiveness between populations. Skulls from New Guinea, and Bathurst and Melville Is, were particularly distinct from other populations. Upper and lower molar row and M1 were long in specimens from New Guinea and short in specimens from Bathurst and Melville Is. However, nasal length, braincase width and bulla length were long in specimens from Bathurst and Melville Is. Possible barriers to population interchange include bodies of water (e.g. separating Bathurst and Melville is from the mainland, and New Guinea from Australia) and unsuitable habitat in the east Kimberley and East Alligator-Arnhem Plateau regions. It is suggested that C. penicillatus had a wider distribution during periods of more mesic climate in northern Australia than at present and that its present distribution is a result of northward contraction since the postglacial thermal maximum. Taxonomic conclusions of the study are the retention of subspecific status for C. p. randi (New Guinea), C. p. melibius (Bathurst and Melville Is) and C. p. penicillatus (all other populations) but not C. p. hemileucurus (locality of type given as 'North Australia').