A rich, earthy smell rose from the cave on the west side of Maunalei Gulch on Lanai.

Wearing headlamps, Maui residents Pauline Fiene and Mike Severns and researcher Storrs Olson stepped into the shadowy interior.

A thick layer of gypsum covered the floor, the likely result of centuries of earthquakes that shook the white plaster from the walls. Some boulder rubble farther in also attested to seismic activity.

Gypsum is a common mineral in Hawaiian lava tubes, but Olson had never seen such extensive deposits in any of the hundreds of other tubes he had explored.

Their boots left prints nearly 4 inches deep in the flaky crystals.

Because gypsum dissolves in water, Olson knew this cave — 2 miles from the sea at an elevation of 540 feet — had been extremely arid for hundreds of years.

Ideal.

The three set to work with their only tools: soft forceps.

Soon, Fiene found herself collecting the bones of a bird in a tight crevice against the wall.

"I’d done this many times in other caves," recalled Fiene, an avid explorer and owner of a scuba diving operation in Kihei that she started with her now-ex-husband, Severns.

Together they were helping Olson, one of the world’s foremost avian paleontologists, locate caves for his research at the Smithsonian Institution in Washington, D.C. The tip on this one had come from Bob Hobdy, a retired botanist with the state Department of Land and Natural Resources who grew up on Lanai.

"There was a kind of crumbly coating on the bones of this particular skeleton, and I brushed it off of a few of the bones," Fiene said by email. "But then something caught my eye and I realized that what I was brushing off might be skin — and maybe even feathers!! It was so exciting, and then I was mortified that I had scraped some off without realizing. This was not anything anyone had seen before in all the hundreds of skeletons that had been collected in Hawaii."

What Fiene had found on that day in February 1993 was the nearly complete skeleton of a Hawaiian ibis, a flightless bird once common in Hawaii that became extinct after the arrival of Polynesians. Ibises, which have long pointy bills, exist today in other places and all can fly.

Scientists speculate that the ibis flew here, then over the years lost the ability to fly because it had no natural enemies. According to Olson, becoming flightless can have evolutionary advantages because flying demands so much energy. If the birds don’t fly, they don’t have to eat as much.

Ibises are small — they grow to about knee-high to an adult human, and come in several colors, including black, white, brown, tan, gold, gray, green, red and combinations of the above.

But no one knew the color of the Hawaiian ibis.

Until recently.

Using a scanning electron microscope, Olson and colleague Carla Dove studied the feather remnants on the bones retrieved from the cave on Lanai.

Their conclusion, published in the September issue of the Journal of Paleontology, is that the Hawaiian ibis, a genus known as Apteribis, had brown-black and ivory-beige feathers, much like the juvenile American white ibis.

The skeleton from Lanai, Olson and Dove write, presents "a rare opportunity to study the feather structure of a bird that was never known historically."

The age of the specimen is unknown, but radiocarbon dates for five Hawaiian petrels found in the same cave put it at 700 to 1,100 years old, they say.

But why did the analysis of the bones, found 18 years ago, take so long?

Olson said he simply got busy with other stuff.

"Lots of studies just get postponed for one reason or another," he said by email. "Other priorities arise. I have published some 160 other papers from 1993 to the present. A couple years ago I realized I had quite a backlog of papers on ibises so made them a priority. The Lanai ibis was one of them."

For Fiene, who has a degree in biology and who has two marine species named after her, the new findings are an opportunity to relive one of her most thrilling experiences.

"I almost felt like I was collecting a dinosaur," she says. "That’s how exciting it was."