Scientists have discovered two new species of flying squirrels, both as big as cats, in the Himalayas.

The flying squirrel is considered to be among the rarest and least studied mammals in the world. Scientists were aware of the existence of a type of the flying squirrel, called the “woolly flying squirrel” — one of the largest species of squirrels believed to be extinct for 70 years until it was sighted again in 1994.After its rediscovery, the International Union for Conservation of Nature categorized the squirrel as “endangered.” However, very little data, and subsequently awareness, of the woolly flying squirrel existed within the scientific community — until scientists started digging into squirrel sightings in the Himalayan region, across India, Tibet, and Nepal.

Researchers have now discovered that what they had mistaken for one species — the woolly flying squirrel — is actually two gigantic species of squirrels: the Tibetan woolly flying squirrel (Eupetaurus tibetensis), and the Yunnan woolly flying squirrel (Eupetaurus nivamons). Published in the Zoological Journal of the Linnean Society, the study explains how the researchers arrived at the discovery after a careful review of museum specimens and published records detailing the woolly flying squirrel.

“These species have been waiting in a museum drawer for a hundred years to reveal their secrets,” Melissa Roberts Hawkins, curator of mammals and a squirrel expert with the Smithsonian Institution in the U.S., who wasn’t among the authors, told National Geographic.

The two new species have differently-shaped skulls — and also, different DNA make-up. Both species can grow more than three feet, and weigh over 2.5 kilograms each.

“[They] are gorgeous, soft-furred squirrels that are genetically and anatomically very different from all other squirrels. And they live on top of the world — in the Himalayas and on the Tibetan Plateau,” Kristofer Helgen, chief scientist and director at the Australian Museum Research Institute, who was involved in the study, said in a statement.

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Helgen also expressed his surprise at the fact that it took scientists so long to discover the species, and “until 2021 for them to get their scientific names.” Although called “flyingsquirrels,” the animals don’t actually fly — they glide, instead, between rocks and cliffs with the help of stretched skin between their front and hind legs.

Both of these species live in areas largely uninhabited by people, at altitudes higher than 15,500 feet — almost half the height of Mount Everest. However, the species still faces the threat of habitat destruction due to large-scale deforestation — particularly the pine woodlands found in elevated areas, where both species dwell.

Fortunately though, “the recent discovery of the species… demonstrates that it might have a considerably wider distribution than previously realized,” the paper noted.

“This discovery is so exciting — That there were two relatively large animals that had gone unreported shows how little we know about the natural world,” John Koprowski, an expert on squirrels at the University of Wyoming in the U.S., who was not involved in the discovery, told National Geographic.

Unfortunately, scientists still know very little about both species — other than the fact that they’re nocturnal, feed on pine needles, and rest in rocky crevices. It’s unclear how the discovery will impact the “endangered” status assigned to the woolly flying squirrel. However, Kristofer Helgen is hopeful the present discovery will take them closer to learning more about the squirrels.

“This is only the beginning — now that they’ve been named, scientists can learn more about how they live,” he said