The Papua who had charge of the animal climbed into the front seat with me and tried to persuade the kangaroo to sit down beside him on the seat, but unfortunately he was not at all successful. Somehow or other the kangaroo wriggled himself free and jumped with his forepaws up on to the steering wheel, so that I had to stop ...

-- Swedish biologist Dr Sten Bergman, taking charge of his newly acquired pet, Dutch New Guinea, 1959.

THE HISTORY OF the Grizzled Tree-kangaroo seems to be largely one of missed opportunities. Despite having been discovered as early as 1828, becoming only the second tree-kangaroo to receive a scientific name, even today -- after 150 years of scientific exploration in New Guinea -- it remains very poorly known.

The distinctiveness of the two subspecies of Dendrolagus inustus recognised here rests on rather slim grounds, for museum specimens are few and little detailed study has been done. The most important difference discerned so far concerns the colour of the face: the forehead is grey or brownish in this subspecies, rather than black in Finsch's Tree-kangaroo (Dendrolagus inustus finschi). Other workers have reported that the colour of the limbs and tail is rather more similar to that of the body in this subspecies, but is more contrasting in Finsch's Tree-kangaroo.

This subspecies reaches a very large size, and males are almost twice as large as females. One captive male weighed 23.18 kilograms. This animal, held in the Gladys Porter Zoo (USA), is by far the heaviest tree-kangaroo ever recorded. While it is possible that this individual was obese, the bones of wild caught specimens suggest that Grizzled Tree-kangaroos sometimes reach an enormous size.

Compared with most other New Guinea tree-kangaroos, the Grizzled Tree-kangaroo is a rather rangy animal, with long limbs and a small head. In this regard it somewhat resembles in shape the terrestrial kangaroos. The males, in particular, show massive development of the forearms. From a distance, its overall colour appears to be grey, although some individuals have a rusty tinge. The tail is very long, grey and often thickly furred. Occasionally, bands of lighter and darker grey can be discerned, giving it a ringed appearance.

It has very large ears for a tree-kangaroo, and when it is sitting in a tree, they characteristically point sideways from the head rather that upwards as in most kangaroos. This doubtless tends to focus the animal's hearing towards the forest below, the direction from which danger is most likely to come. Most tree-kangaroos tend to do this, but because the ears are so large it is particularly noticeable in this species.

A large, naked callosity is present at the base of the tail on the upper side. This extensive callosity is unique to Dendrolagus inustus among the tree-kangaroos. It may result from an unusual resting posture in which the tail projects forward between the legs, the callosity forming a 'seat'. It does not result solely from abrasion, however, as it is also present in pouch young. Other tree-kangaroos occasionally adopt this posture. Indeed, it is the typical posture in which all female kangaroos and wallabies give birth.

The Grizzled Tree-kangaroo is widely distributed over a large area of low and middle elevation rainforest in far western New Guinea and surrounding islands. It may be common in some areas such as,the northern Vogelkop Peninsula, where sight records have recently been made.

In captivity it is crepuscular, being most active at dawn and dusk. It is a more active animal than Ifola (Dendrolagus dorianus notatus), with which it has been compared in a study of activity patterns.

Almost nothing is known of its social life. A group consisting of a female and her young (sharing a tree) and what was probably a male in an adjacent tree, has been observed by day (Mr Poulson, personal communication).