Giant cloud rat species weighing about a kilogram once roamed the Philippines based on the discovery of a team of scientists from the University of the Philippines (UP), National Museum of the Philippines (NMP), and the US Field Museum of Natural History.

In a news posted on the UP website on Friday, April 23, the scientists based their findings on the fossilized remains of the three extinct giant cloud rat species, locally known as "buot" or "bugkun," which were known to have lived thousands of years ago.

The newly recorded fossil species were unearthed from Callao Cave and several adjacent smaller caves in Peñablanca, Cagayan.

Scientists Janine Ochoa, Armand Mijares, Philip J. Piper, Marian C. Reyes, and Lawrence R. Heaney named the newly-identified species of rats unique to the Philippines as Carpomys dakal, Carpomys melanurus, and Carpomys phaeurus.

They added that some specimens of all three of the new fossil rodents occurred in the same deep layer in the Callao Cave where the Homo Luzonensis, an endemic human species, was discovered in 2019 and was known to have lived about 67,000 years ago.

"The two that became extinct (more recently) were giants among rodents, both weighing about a kilogram. They were big enough that it might have been worthwhile to hunt and eat them," Heaney, a Negaunee Curator of Mammals at the Field Museum of Natural History in Chicago, said in the UP statement.

By comparing the fossils to the 18 living species of giant cloud rats, the researchers have a decent idea of what these three new fossil species would have looked like, a separate press release from the Field Museum in Chicago said.

"The bigger ones would have looked almost like a woodchuck with a squirrel tail," Heaney said.

"Cloud rats eat plants, and they’ve got great big pot bellies that allow them to ferment the plants that they eat, kind of like cows. They have big fluffy or furry tails. They’re really quite cute," he added.

In UP's statement, NMP zooarchaeologist Marian Reyes said "these giant rats and their relatives are members of an ancient branch on the tree of life that arrived from the Asian mainland about 14 million years ago and live only in the Philippines."

Reyes added that the discovered rats with "furry" or "fluffy" tails and striking fur colors, typically lived in trees and ate leaves, buds, and seeds.

"Our records demonstrate that these giant rodents were able to survive the profound climatic changes from the Ice Age to current humid tropics that have impacted the earth over tens of millennia. The question is, what might have caused their final extinction?" asked Piper, a co-author based at the Australian National University.

"A clue might be in that the last recorded occurrence of two of the species is around 2,000 years ago or shortly after. This is after the first arrival of agricultural societies and the introduction of animals like domestic dogs, pigs, and macaque monkeys in Luzon," said Mijares of the UP Diliman Archaeological Studies Program, who also headed the excavations of Callao Cave.

Mijares noted that "while we can't say for certain based on our current information, this implies that humans likely played some role in their extinction."