At the age of 26, Dollar has lived through all of these miseries and more. And yet every year, after a few obligatory months in the United States to gather school credits and grant money, he bolts back to the island, slipping comfortably into this ancient world of taboos, forests, and ever-so complicated modes of transportation. By now, Dollar has trapped and radio-collared 16 fossa and bagged and examined hundreds of samples of their droppings. He knows how they look, how they sound, and even how they smell (musky with a hint of rancid meat). There are times, he believes, when he even knows how fossa think.

The payoff for all this zeal has been a biologist’s bonanza. So little is known about the fossa, and so much of what is known is wrong, that nearly everything Dollar documents is new to science. Figures on fossa weights, for instance, tend to be based on zoo specimens and therefore exaggerated, and the fossa diet is only dimly understood. Until Dollar noticed that the animal’s scat sometimes smelled fishy, no one knew that fossa eat fish. Until he tracked them during the day, biologists assumed the animals were nocturnal. Now we know they are cathemeral, hunting and napping around the clock, on no set schedule.

Inevitably, science has stripped the fossa of some of its mythical mystery and power (even the most vicious fossa, we now know, couldn’t kill a cow). But Dollar’s work has also demonstrated the fossa’s pride of place. The animal is the lynchpin of Madagascar’s ecosystem, he believes, filling the same role that lions, cheetahs, and leopards combined fill in Africa. Although there are seven other native carnivore species on the island, the fossa is largely credited with keeping lemur populations in check. And it rules not just the dark forest of Ampijoroa, but the whole ring of trees at the edge of this otherwise denuded 1,000-mile-long island.

Unfortunately, we still don’t know how many fossa there are, how exactly they hunt and breed in the wild (though a fossa pair was filmed mating in a tree this past year), or how habitat losses are affecting their numbers. The island’s ecology depends on a mystery, it seems—one that Dollar is doing his best to unravel.

One evening, early in this trip, Dollar and I sat down together at a greasy wooden table next to a corrugated shack. In our hands were bottles of orange Fanta and Three Horses beer, coated in congealed blood from the zebu meat next to which they were stored. On our plates was a supper that would have done a French penal colony proud: zebu stew, rendered inedible by bone shards, and rice with rocks. Over the years, Luke has destroyed four molars on such fare and, tonight, the photographer, Roy Toft, clamped down with an astounding and sickening crunch.

All around us lay base camp: a few plain cement buildings and palm-thatched tenting sites administered by Conservation International and used mostly by lemur researchers. Around the buildings lay the dry, deciduous forest of the Ankarafantsika Reserve Complex, and around the complex lay the fields and paddies of the second largest rice-growing region in the country. Seen from above, the setting might have looked like an enormous misshapen dartboard, with us at the bull’s-eye. But we had yet to hit our target.

After several months in Madagascar, Dollar had lost his usual twenty pounds, and had the rangy look and stoic attitude of someone who’s been roughing it for a while. He wore sandals and tank tops around camp, set off by traditional Malagasy wraps called lambas. But even set off by such odd apparel, his blue eyes, fine-boned face, and boyish haircut gave him the rakish good looks of the actor Brendan Fraser. As a former child actor himself, Dollar seemed perfect for the role of intrepid explorer.

When I asked how he would classify a fossa biologically, he laughed. “I guess I’d still call them killing machines,’’ he said, his Alabama roots apparent only in the easy rhythm of his words. “It is equipped to take anything it would encounter in its natural environment.’’ The fossa is as agile as a squirrel, he said, using its luxuriant tail for ballast and balance when leaping from branch to branch. Yet the fossa’s muscle and might are closer to that of a clouded leopard, its only rival in arboreal athleticism. “It’s like a small puma,” Dollar said, “with the tenacity of a mongoose.”

KING KONG VS. GODZILLA

When people first set foot in Madagascar 1,500 years ago, the island was a bit like King Kong’s Skull Island: a place of rare and monstrous beasts, many of them throwbacks to a previous era. Some 165 million years previous, Madagascar had split off from Gondwanaland, preserving many of that ancient continent’s species and giving rise to some astonishing new ones. There were blind snakes, screaming geckos, and upside-down trees. There were 1,000-pound elephant birds, Aepyornis maximus, that stood 10 feet tall and laid eggs containing nearly three gallons of liquid. As lemur researcher Alison Jolly puts it: “The world of Madagascar tells us which rules would still hold true if time had once broken its banks and flowed to the present down a different channel.”

Elsewhere on the planet, lemurs died out and monkeys took their place. But in the alternate universe of Madagascar, lemurs ruled. Some species walked on all fours, some swung through trees, others probably inched their way up trunks like slow, deliberate koalas. The largest of their kind, Archaeoindris fontoynontii, was the size of a modern-day gorilla—too large, one would think, to be threatened by predators. But there was another giant around as well: Cryptoprocta spelia, the fossa of all fossa.

At six feet (not counting its tail) and 200 pounds, the spelia would have had the strength of a lion. Just when and how it died out is a matter of debate because paleontologists have yet to uncover a good mammalian fossil record in Madagascar. But if it lived long enough to confront the first human settlers, that might explain why the fossa looms large in local folklore—and why it still terrifies the Malagasy.

Like the Loch Ness monster or the Tasmanian tiger, the spelia is rumored to survive in some remote pocket of nature, and the rumors excite even skeptical biologists. In November, Luke Dollar trekked to one of the beast’s supposed stomping grounds: Zahamena National Park in northeast Madagascar, also known as the Impenetrable Forest. Zahamena is so uninviting that no one has made any detailed maps of its interior. Dollar found no trace of spelia, but most of the forest remains unexplored. —Vicki Croke

The comparison is apt. Most biologists, noting the shape of the fossa’s skull and it’s low-slung body, now classify it as a member of the mongoose family. But for years it was classified as a feline because of its catlike molars and overall shape. Either way, the animal’s hybrid appearance and dual citizenship offer a glimpse of how the two families’ common ancestor might have looked and behaved 35 million to 40 million years ago.

As Dollar talked, the camp mascot—a common brown lemur named Piper—leapt up onto his lap for a scratching. In the wild, a fossa’s face is often the last thing a lemur sees. But no one has ever seen the killing done. Biologist Clare Hawkins, who has captured an astonishing 43 fossa, believes the animal hunts alone, and that it stalks and rushes its prey like a cat. “There is absolutely no nervousness,’’ she says. “They just get on about their business.’’ Because he often finds the remains of a kill near trees where lemurs gather to rest, Dollar suspects that fossa often strike sleeping lemurs, or ones that are just waking up from afternoon naps. But most of the time stealth is unnecessary.

“The fossa is capable of explosive speed,’’ Dollar says. The attack, he adds, is straightforward in the extreme: “Wham! Face first, head bite, then front claws slashing the stomach and eviscerating. Puncturing the cranium and crushing the jawline in one bite. Front claws opening the body cavity.’’ Given the chance, Dollar says, a fossa will “eat anything with a heartbeat: lemurs, reptiles, chickens, fish, wild pigs.”

That so peaceful a place should depend on such a killer is one of nature’s great ironies. For decades, naturalists on the island have conveniently ignored such butchery. “Of Madagascar I can announce to naturalists that this is truly their promised land,” French explorer Joseph-Philibert Commerson wrote in 1771. “Here Nature seems to have created a special sanctuary whither she seems to have withdrawn to experiment with designs different from any she has created elsewhere.” The island has no truly venomous snakes or big cats, no bears or wolves or man-eating reptiles. Yet even paradise needs a killer or two. Predators keep prey populations in check, which saves plants from being overgrazed. By acting as the lemur’s worst nightmare, the fossa helps maintain the island’s blissful natural balance.

But for how long? Since humans first arrived here 1,500 years ago, 17 species of lemur have died out, as well as multitudes of other species. What remains clings to a mere 10 percent of the island’s original undisturbed wilderness. Flying over Madagascar or driving though it, the pitiful state of the environment is relentlessly apparent: mile after mile of scraggly crops where forests used to stand, eroded hillsides where natural wonders once lived. The island looks like a victim of war: naked, scarred, battered, burned.

What’s left may be the single most precious, most species-rich area in the world. Eighty-three percent of Madagascar’s wildlife is unique, including 8,000 of its 10,000 plant species and two-thirds of the planet’s chameleon species. Still, if the island’s health depends on the fossa’s brutal care, then that is a precarious balance indeed. Although the World Conservation Union long listed the fossa as vulnerable, it has recently changed its status to endangered. Dollar guesses that there may be fewer than 2,000 of the animals on the island. But how varied is their physiology and behavior? How stable are their populations? Answering those questions may take a lifetime.

In the meantime, Dollar’s trapping and tracking work, helped along by volunteers from the Earthwatch Institute, has shown that fossa density in Ampijoroa is surprisingly low. In three weeks in 1998, in the neighboring forest of Tsimaloto, he caught three fossa in live traps and documented another three with motion-sensitive cameras. Given the similar terrain and lemur life here, he expected to trap 10 to 20 in three months. By project’s end, he would catch only two.

Dollar’s conclusion is sobering: Although fossa live in every kind of forest on the island—lowland and montane rain forest, dry deciduous forest, and spiny desert—they may not always be able to put down roots. “As soon as there’s any habitat disturbance, fossa fall out,’’ he says.

In Ampijoroa, lemur researchers aren’t the only ones combing the forest. Local honey cutters chop down whole trees to collect nectar-filled hives; loggers search for rare woods; poachers kill rare animals. One day, I saw a local park guardian collecting firewood in the forest, against park rules. On another day, a poacher appeared from the forest while we were tracking. “I don’t have anything,” he protested, hurrying off. But we soon discovered his six-foot blowpipe stashed under some brush. When Dollar pressed his mouth to one end and exhaled, a rusty six-inch dart fell to the ground with some cotton wadding. The dart had lemur fur on it.

Today, on our last day in camp, it seems as if our own hunting will be less well rewarded than the poacher’s. Though we glimpsed the fossa this morning, we weren’t able to catch it. Still, Dollar isn’t ready to give up. While the rest of us read books and write letters in base camp as we wait for a rusted minivan to take us to the airport, Dollar hikes back up the trail one last time to check the traps. Within minutes, the camp is roused by cries of “Fossa! Fossa!” over the two-way radio. A little later, Dollar strides into the clearing carrying Tasha’s limp, sedated form.

Up close, the fossa is even more spectacular than she had seemed in the forest that morning. As sinewy as a mountain lion and as slick as root-beer taffy, she has enormous paws and a long tail that dangles below Dollar’s cradling arms. Her underbelly bears a creamy blaze, and even though she has just killed and eaten an entire chicken—including the comb, feathers, and toes—she is spotlessly clean.

From all around the camp, staff members and volunteers, villagers and their children, converge on the veranda, packing themselves around the battered table where Dollar has laid his prize. He removes the thick red, white, and blue leather collar, number 448808, and puts the channel out of service. Then he and a veterinary volunteer measure everything measurable.

This terror of the forest weighs only 14 3/10 pounds, and her other measurements, though typical for a fossa, seem equally tame. Her canines are 6/10 inch. Her neck circumference is 9 3/10 inches. Chest circumference: 13 inches. Full body, no tail: 28 inches. Full body with tail: 56 inches. Heart rate: 140 beats per minute.

Once the blood samples have been taken and the study is complete, the circus begins. Everyone wants to pose with the fossa, and so she is passed from hand to hand, photographed by one instant camera after another. It is an unseemly, discomforting scene, but I can’t help joining in. As the forests of Madagascar and other Edens fall, and as species after species tumbles toward extinction, we all yearn to hold onto the survivors a moment longer—to touch something wild and mysterious before it disappears. And yet even as we hold the fossa in our arms, we know its true nature has eluded us. It is floating through the trees even now: a rumor, a shadow, A story to tell children. A shape as ephemeral as smoke.