I had barely recovered from the adrenalin rush of touching down on a tiny airstrip hacked out of the Guyanese rain forest when my heart sank. I had expected to be greeted by a group of Amerindian porters hired to carry a ton of food and field equipment to the summit of Mount Ayanganna, clearly visible 40 kilometres away.

Instead, the porters – known locally as drudgers – were about to head home. They had been double-booked, and were just getting back from an excursion with another group of biologists.

For me, turning back was out of the question. As a curator of mammalogy at the Royal Ontario Museum in Toronto, I had come to 2,000-metre-high Mount Ayanganna to conduct the first known survey of mammals in the area.

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Illegal gold mining was threatening many local species downstream on the Potaro River, but I was headed upriver to find out what species of mammals lived on this pristine and remote flat-topped mountain of western Guyana, the smallish South American nation north of Brazil and east of Venezuela.

I was out to document the poorly studied, small-sized mammals such as bats, rats and opossums.

If I was really lucky, I might discover a species or two that had so far managed to escape human detection.

Contrary to conventional wisdom, more plant and animal species are being discovered than are going extinct. And not only tiny, innocuous organisms. More than 9,000 new species of insects were documented in 2009 (the most recent data), but there were also, says the International Institute of Species Exploration at Arizona State University, 41 mammal species described as new that year, such as several tube-nosed bats and an arboreal rice rat. (While 196 mammals are listed as critically endangered, the international Red List of Threatened Species reported no mammals going extinct in 2009.)

While I can't deny the personal pride involved, the discovery of previously unknown species has much wider implications than bringing recognition to an otherwise obscure academic researcher.

A new species could contribute to the next medical cure to help heart-attack patients, help develop a new natural product to rival rubber, or spur research into a promising new crop.

A deeper knowledge of the world's biodiversity also bolsters understanding of Earth's intricate ecosystem and how its health provides a crucial hedge against global warming and climate change.

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Bats, for example, play an important role in the regeneration of tropical forest by acting as seed dispersers and flower pollinators.

The continuing discovery of new species is due in large part to revolutionary technologies in molecular biology that have allowed researchers to peek inside the cells of organisms and distinguish between plants and animals that superficially appear similar: For example, the Tasmanian tiger looks somewhat like the Asian big cat, but it's actually an Australian marsupial.

DNA analysis takes this example to a finer level of study: Thanks to a 2001 study at the Laboratory of Genomic Diversity of the National Cancer Institute in Maryland, what we once called the African elephant is now split into two different species, the savannah elephant and the forest elephant.

But the larger, better-known mammals represent only a quarter of the species that populate tropical forests. Much less is known about the huge variety of smaller mammals, weighing less than a kilogram.

Even with the help of modern technology in the lab, however, new discoveries still require a scientist to venture out from the comfort of the office to some of the most remote and inhospitable parts of Earth.

Charles Darwin spent nearly five years from 1831 to 1836 on a voyage of discovery exploring the natural wonders of the world while circumnavigating the globe. His younger contemporary, Alfred Russel Wallace, was nearly as celebrated an explorer and biologist. Wallace traipsed through the Amazon for four years and then spent eight more traversing the Indo-Malaysian archipelago.

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Between them, the two identified hundreds of hitherto unknown organisms, ranging from barnacles to butterflies. This inquisitive curiosity led them to the Holy Grail of life – the theory of evolution by natural selection.

The Secretariat of the Convention on Biological Diversity in Montreal estimates that there are 5,000 to 7,000 researchers worldwide involved in the scientific business of classifying species. At the Royal Ontario Museum, 17 curators conduct biological field expeditions searching for anything from mushrooms in Thailand to fish in Ecuador.

In 1984, I followed in the footsteps of Randolph Peterson, ROM's mammal curator at that time and my former zoology professor at the University of Toronto, by becoming a researcher of mammals, particularly bats, which were his specialty.

I have identified a total of seven new species (all bats) over the past two decades, a pretty good record for a mammalogist (entomologists have it easy by contrast – there are about one million known species of insects, but fewer than 6,000 mammals).

That first mountain expedition to Guyana was in 2002. But it would take a collaborative effort involving three other biologists and more than a decade of research to officially conclude the successful discovery of a new species of opossum.

Despite almost two centuries of progress, some aspects of biological fieldwork have not changed. GPS, satellite phones and planes have made exploration easier and safer, but, as I realized standing helplessly at the remote airstrip in Guyana, some places remain so isolated that hoofing it is the only way to get there.

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Help from the indigenous people is indispensable, and luck is as critical as technology to a successful mission. Now I had no guides and no one to help me carry my gear to Mount Ayanganna.

But my luck soon turned. The guides told me that six other Amerindians from their village near the Brazilian border were panning for gold nearby. I persuaded the lead drudger to find them, and ask them to join our expedition.

Within 24 hours, we had all assembled under a makeshift plastic tarp crammed against the dense jungle tangle beside the airstrip. We would spend the next six weeks eating, sleeping and playing dominos together.

But I first had to negotiate with one of a group of itinerant gold miners from Brazil who had illegally sprung up near the airstrip. Putting aside my misgivings about their illicit and environmentally damaging activities, I made a deal with the devil: In a fractured mix of Portuguese, Spanish and English, I rented a boat to ferry us to the head of the trail to the summit of Mount Ayanganna, pioneered a year earlier by an American botanist.

As we finally sailed upriver the next day, the environmental damage caused by mining was all too apparent.

Big, rusty dredges were excavating the river bed for gold, leaving a deadly spew of silt and toxic mercury (used to extract the ore) in their wake.

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Clearly, the area's biological treasures needed to be catalogued before it was too late.

We reached the trailhead the next morning. Our first camp was just an three-hour, three-kilometre hike over what seemed like an endless mat of gnarly roots broken up with several creek crossings over "monkey bridges," ridiculously slippery tree falls that made-up our meandering trail through the tropical rain forest.

It took the drudgers four days and six round-trips to carry all the supplies up from the river.

We started the biological survey by setting nets to catch bats, and traps for rodents and opossums.

The opossum is one of the minority of marsupials found in the Americas rather than in Australia. They live mainly in southern climes, but one species, the Virginia opossum, has been slowly moving north in Ontario, and is now common as far as Guelph.

It normally lives in the forest, but this omnivore has also adapted to urban environments and the cornucopia of food available in household garbage. Another species, the grey short-tailed opossum from South America, is an important model lab animal for immunological research related to human diseases.

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After a week at the first camp, we ascended for three hours to our second base at an altitude of 1,100 metres. The weather was getting cooler and wetter.

On our first morning at the second camp, I noticed that the spring-loaded door had closed on a trap set the previous night, precariously perched on an angled tree trunk. Excitedly, I cracked open the door to peer inside.

A small opossum, with characteristically large eyes, was staring back at me.

However, it was impossible to tell precisely what species it was, because so few South American opossums have been caught and studied. I closed the door and cheerfully brought the trap, with opossum inside, back to camp.

To properly study the opossum and as documentation of the species diversity in this poorly known region, I had to euthanize it and prepare it as a specimen: I examined the external features and took measurements of its hind foot, ear, tail and total length for comparison with other, known species.

I noticed its large eyes were surrounded by black fur and that it had a pointy snout, long thin legs, a curling tail that could grab onto branches, as well as opposable big toes on the hind feet that helped it move around in the trees. These characteristics clearly placed it in the group of small mouse-like opossums, but the greyish fur on the underbelly and overall size did not match any species I knew.

By now, I suspected our little Guyanese catch was a hitherto undocumented species. But I had to do more work back at the museum in Toronto to make sure.

Competition is intense among scientists for bragging rights to new species. There are no prizes for coming second, particularly when it comes to giving a species its official scientific name.

In 2009, a fellow researcher in Ottawa alerted me to the fact that a group of Chinese biologists were about to identify a species of bat that might be identical to one I had been working on. We were able to negotiate a compromise and I ended up collaborating with the Chinese on a joint paper describing the new southwestern Chinese horseshoe bat, Rhinolophus xinanzhongguoensis.

Identifying the Guyanese opossum turned out to be more difficult than expected. Looking at the skeleton and teeth only got me as far as the genus known as slender opossums, but still no clue on the specific species.

I made two more field trips to survey the other highest flat-topped mountains in Guyana. By the time I returned from the third expedition in 2004, I had collected a total of six of the mysterious opossums.

My next move was to analyze the animals' molecules and compare them to an existing genetic reference database called the DNA barcode to see if they matched a known species. In the case of the opossum, however, the usually reliable technique failed to produce results.

Once again, luck was on my side. While mulling over my dilemma, I received an e-mail in 2008 from Rob Voss, an opossum expert at the American Museum of Natural History in New York. He wanted to update the classification of the entire group of opossums found in the Americas and was keen to visit ROM to examine our specimens.

I was so happy to have his help (along with that of Sharon Jansa and doctoral student Juan Diaz-Nieto at the University of Minnesota). Dr. Voss is one of a dwindling band of taxonomists, the experts who study the classification of species. The newer fields of ecology and molecular biology have received greater attention in academia over the more recent years. There are "not many new U.S. or Canadian students now working on mammalian taxonomy," he says, because there are so few academic jobs.

The bright side is that the next generation of taxonomists are from tropical countries where most of the biodiversity is found, such as those in South America.

The story will soon have a happy ending: We will formally unveil the scientific classification of the Pakaraima slender opossum later this year in the scholarly journal American Museum Novitates. The new species is named after the 500-metre-high plateau that gives rise to Guyana's distinctive flat-topped mountains.

Much work remains to be done, both in the lab and in the field, to document life on Earth.

Scientists have so far identified about two million species, but taxonomists estimate that between 10 million and 100 million species are still waiting to be discovered.

"My long-term studies in just two hectares at Yasuni [Ecuador] turned up 100,000-plus species of arthropods so far," says Terry Erwin of the Smithsonian Institution in Washington, D.C., and "there are 17 billion hectares in the Amazon Basin with 450 different kinds of forests. … You do the math."

But "there is not enough data from enough global points," he adds, even to make a guess at the total number of species of living organisms.

Technology and genetic analysis are helping to speed up these discoveries. But still, deep in the rain forests and oceans lie the last biological frontiers in the world, where few biologists have set foot – and where many unfamiliar species remain to be detected.

Burton Lim is a journalism fellow at the Munk School of Global Affairs at the University of Toronto and assistant curator of mammalogy at the Royal Ontario Museum.