IS it a deer? Is it a goat? No it's Pseudoryx nghetinhensis, or the Vu Quang ox, recently identified as an entirely new type of mammal and the oldest existing species of cow. But far from chewing cud in a paddock, this cousin of the domestic cow inhabits lush, primaeval rainforest in the isolated mountains of the Vietnam-Laos border. Weighing about 100 kilograms, the Vu Quang ox has dainty hooves, large face glands, black and white markings and distinctive sharp straight horns half a metre long. It was discovered last year by a team of scientists led by Hongkong-based zoologist Dr John MacKinnon while exploring the Vu Quang nature reserve, 270 kilometres southwest of Hanoi. The deer-like creature with the habits of a goat is described as one of the most significant zoological finds of the century. ''Most of us feel we know all the large mammals that are out there, and when something like this comes along we are floored,'' said Dr John Robinson of the New York-based Wildlife Conservation Society. Dr MacKinnon said the discovery was significant on three counts. ''Firstly, it is the first new large mammal species identified for over 50 years. ''Secondly, in terms of wildlife management, a new species could be vital in providing a new gene pool for domestic cattle. ''Thirdly, it becomes a flagship species which is useful in gaining funds to save the whole region,'' said Dr MacKinnon. The former Oxford scholar said the initial discovery came as a complete surprise. ''I went to the area to research species diversity. On the first night I sent some of the team to interview villagers. They came back and said there were two species of goat in the area. ''This intrigued me. I knew the serow [a breed of antelope] lived in the area but didn't know of any other goat-like creatures. So when they described it as bigger than a serow I became interested as I realised I was on to something unique. It was very exiting,'' said Dr MacKinnon. Although he has yet to see a live Vu Quang ox, Dr MacKinnon has ample evidence, including many witness accounts, hides and more than 20 skulls. ''We believe the Vu Quang ox has a population of a few hundred spread over about 4,000 square kilometres, which makes it hard work finding them.'' Efforts to film the ox with automatic cameras will now be stepped up. Since the discovery of the ox, the Vu Quang Nature Reserve has trebled in size and logging has reduced. ''The Dutch Government is interested and has donated close to US$2 million (about HK$15.56 million) to fund a five-year project to increase the size of the reserve, train conservation staff and develop industry in areas surrounding the reserve,'' said DrMacKinnon. ''Of course, they also see the potential for tourism and although the roads are too poor for tourism at the moment, it is recognised as a lifeline to save pristine forest from development.''