The Philippines was once home to three previously unknown species of an unusual group of rodents with fluffy tails known as "giant cloud rats", according to a new fossil discovery.
All three of the newly discovered species (Crateromys ballik, Carpomys dakal, and Batomys cagayanensis) are thought to be extinct.
The discovery was made by an international team of researchers, including from The Australian National University (ANU).
Buot, as the giant rats are known locally, are only found in the Philippines and typically live in trees and eat leaves, buds and seeds.
Their evolutionary history in the area stretches back around 14 million years, when ancient relatives of these rodents first arrived in the Philippine archipelago from the Asian mainland.
Several of the newly recorded fossil species came from Callao Cave, where a previously unknown species of human, Homo luzonensis was found in 2019, as well as smaller caves in Cagayan Province.
"Specimens of all three of the new species of fossil rodent were found in the same deep layer of the cave as the enigmatic Homo luzonensis indicating that they co-existed some 60,000 years ago," co-author Professor Philip Piper from ANU said.
"Our records show they were able to adapt and survive profound climatic changes over millions of years, so the question is what might have caused their final extinction?"
The timing of the last recorded occurrence of two of the species might offer a clue - 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 to the Philippines.
"While we can't say for certain, this implies that humans likely played some role in their extinction," said Professor Armand Mijares from the University of Philippines, who led the excavations of Callao cave.
According to Dr Lawrence Heaney from the Field Museum of Natural History in Chicago, these recently extinct fossil species "not only show that biodiversity was even greater in the very recent past. The discovery also shows the two rodent species that became extinct just a few thousand years ago were giants among rodents, both weighing about a kilogram. They were big enough that it might have been worthwhile to hunt and eat them."
"This project has demonstrated that future studies focusing on the fossils of small mammals may tell us a great deal about how environmental changes and human activities have impacted the exceptionally distinctive biodiversity of the Philippines," added Dr Janine Ochoa, Assistant Professor of Anthropology at the University of the Philippines and lead author of the study.
Marian Reyes, a zooarchaeologist from the National Museum of the Philippines, highlighted the importance of preserving collections of animal bones.
"Some of these fossils were actually excavated decades ago, in the 1970s and 1980s, and they were in the museum, waiting for someone to have time to do a detailed study. It was a surprise to find that the collections contained not one, but three buot or giant cloud rat species that were previously unknown."
The study has been published in the Journal of Mammalogy.