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The Pakaraima slender opossum, a new species named after the 500-metre high plateau in western Guyana that gives rise to Mount Ayanganna and other flat-topped mountains. (Francis X. Faigal)
The Pakaraima slender opossum, a new species named after the 500-metre high plateau in western Guyana that gives rise to Mount Ayanganna and other flat-topped mountains. (Francis X. Faigal)

How I discovered a new species of opossum, and why it matters Add to ...

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.

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