Breakthrough: Extinct giant rodents discovered in the Philippines

Posted by UP Media and Public Relations Office

Fig. 1. Artist’s conception of the three extinct cloud rats, based on their living relatives. From the top, Crateromys, Carpomys, and Batomys. Drawing by Velizar Simeonovski, Field Museum of Natural History.

Three giant cloud rat species were discovered to have lived in the Philippines simultaneously as the oldest human species (Homo luzonensis) found in the country. But two of the rodents went extinct only after 2,000 years ago.

A team from the University of the Philippines (UP), the Philippine National Museum, and the Field Museum of Natural History of the USA have since 2017 studied fossil remains sifted from the earth in several caves in northern Luzon from which they discovered the three extinct species unique to the Philippines.

The discovery was recently published in the Journal of Mammalogy. Read the full article here.

Fig. 2. Collage of fossil cloud rat teeth. Upper molars of Crateromys new species on the left. Lower mandibles on the right: top, Carpomys new species. Middle, Batomys new species. Bottom, Crateromys new species. Photos by Lauren Nassef, Field Museum of Natural History.
Fig. 3. Lower molar teeth of the new giant cloud rat, Carpomys new species (left), compared with the two living species of Carpomys (middle) plus their close relative, Musseromys (right). Photos by Lauren Nassef, Field Museum of Natural History.

“These are three previously unknown species from an unusual group of rodents, locally known as buot or bugkun, and known in English as giant cloud rats, that live only in the Philippines,” says Dr. Janine Ochoa, Assistant Professor of Anthropology of UP Diliman and lead author of the journal paper.

According to the co-author, Dr. Lawrence Heaney, Negaunee Curator of Mammals at the Field Museum of Natural History in Chicago: “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.”

“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,” says co-author Marian Reyes, a zooarcheologist at the National Museum of the Philippines.

She describes the buot typically as living in trees and eating leaves, buds, and seeds. She also says that all of them have furry or fluffy tails and striking fur colors.

The scientific names of the three new species of fossil cloud rats were chosen using vernacular terms from Philippine languages. The largest of the fossil cloud rats is Carpomys dakal, named so because it is much larger compared to the known living species in the same genus, Carpomys melanurus and Carpomys phaeurus. Dakal means big or large in several languages in northern Luzon, including in the Itawes, Ibanag and Agta languages. The second fossil species, Crateromys ballik, is slightly smaller than the living Crateromys species on Luzon, Crateromys schadenbergi. Ballik means small in the Dupaningan Agta language. The third species, Batomys cagayanensis, is named after the place where the archaeological sites are located, the Cagayan region of northeastern Luzon.

At a crossroads with humans

According to the researchers, the newly recorded fossil species came from Callao Cave and several adjacent smaller caves in Peñablanca, Cagayan Province. 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 to have lived about 67,000 years ago.

Fig. 4. Callao Cave interior. Photo by Patricia Cabrera.
Fig. 5. Callao Cave excavation. Photo by Armand Mijares.

One of the new fossil rodents is known from only two specimens from that ancient layer, but the other two are represented by specimens from that early date up to about 2,000 years ago.

“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?” asks Prof. Philip Piper, a co-author based at the Australian National University asks.

“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,” co-author Dr. Armand Mijares of the UP Diliman Archaeological Studies Program, who headed the excavations of Callao Cave, says.

“While we can’t say for certain based on our current information, this implies that humans likely played some role in their extinction,” Mijares argues.

Fig. 6. Dr. Armand Mijares in excavation pit, Callao Cave. Photo by Dawn Satumbaga.

Ancient Philippine biodiversity

According to Ochoa, the extinct mammals previously known from Luzon were all quite large. They included two types of elephants, a species of rhinoceros, a giant hog, and relatives of the living dwarf water buffalo called the tamaraw.

“There has been virtually no information about fossils of smaller-sized mammals,” she points out. “The reason is probably that research had focused on open-air sites where the large fossil mammal faunas were known to have been preserved, rather than the careful sieving of cave deposits that preserve a broader size-range of vertebrates including the teeth and bones of rodents,” Ochoa explains.

“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,” says Reyes. “When we began to analyze the fossil material, we were expecting fossil records for known living species.”

“To our surprise, we found that we were dealing with not just one but three buot or giant cloud rat species that were previously unknown,” Reyes adds.

“Our previous studies have demonstrated that the Philippines has the greatest concentration of unique species of mammals of any country, most of which are small animals, less than 200 grams, that live in the tropical forest,” Heaney adds. “These recently extinct fossil species only show that biodiversity was even greater in the very recent past.”

Article by Dr. Janine Ochoa ([email protected]), Dr. Armand Mijares ([email protected]), and Dr. Lawrence Heaney ([email protected]). For inquiries, please email the authors.