Fossils of extinct “giant cloud rats” found in the Philippines

Piecing together fossil remains of jaws and teeth in the Philippines, archaeologists have unearthed evidence of three new giant cloud rat species that lived in the treetops until just a few thousand years ago.

Illustration showing how the three new species of fossil cloud rats might have looked.
Illustration showing how the three new species of fossil cloud rats might have looked. Credit: © Velizar Simeonovski, Field Museum.

Two of the species, which come from the Phloeomyini tribe, would have been around for about 60,000 years, they report in the Journal of Mammalogy, suggesting the mammals were extremely resilient before they suddenly disappeared.

“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,” says co-author Philip Piper from the Australian National University.

“The question is, what might have caused their final extinction?”

The remains were discovered with those of two species of ancient humans in and around Callao Cave on Luzon Island, where excavations seeking insights into early hominins in the Philippines turned up the recently described Homo luzonensis.

The two enduring cloud rat species seem to have disappeared around the same time that pottery and Neolithic stone tools appeared and when dogs, domestic pigs and possibly monkeys were introduced, says co-author Armand Mijares from the University of the Philippines.

Callou cave site where the fossils were found.
Callao Cave site where the fossils were found. Credit: Patricia Cabrera

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

After discovering the fragments, the team added them to existing fossils excavated several decades ago that were languishing in a museum. They spent “days and weeks staring through microscopes,” says co-author Lawrence Heaney from Chicago’s Field Museum, US, comparing them to the 18 living species of cloud rats to identify them.

Altogether, they had only 50 or so fragments to work with.

“Normally, when we’re looking at fossil assemblages, we’re dealing with thousands and thousands of fragments before you find something rare and really nice,” says lead author Janine Ochoa, also from the University of the Philippines.

“It’s crazy that in these 50 fragments we found three new species that haven’t been recorded before.”

The new herbivorous species, Batomys cagayanensis, Carpomys dakal and Crateromys ballik, add to the richness of the region’s native fauna history.

“Clearly, Philippine mammals were even more diverse in the recent past than they are now,” says Heaney, “and that is saying a lot, given that the Philippines has the highest concentration of unique mammals of any country.”

Photograph of some of the cloud rat fossil teeth.
Photograph of some of the cloud rat fossils. Credit: Lauren Nassef, Field Museum

The newly discovered species would have weighed around one kilogram or more (at least double the size of the average common rat) and been rather endearing, he adds.

“The bigger ones would have looked almost like a woodchuck with a squirrel tail. 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.”

Until recently, fossil discoveries in the region focussed on large mammals, identifying native deer (Rusa Marianna), warty pigs (Sus philippensis), suid (Celebochoerus cagayanensis) and dwarf water buffalo(Bubalus), which the authors say leaves vast gaps in our understanding of the island’s small mammals.

“Clearly discovery of these fossil species will change our previous perceptions in important ways,” they write, “and highlights the likelihood that further studies of fossil Philippine small mammals will substantially impact our understanding of the evolution and ecology of mammals in this extraordinary centre of endemic mammalian diversity.”

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