Bones of Extinct Giant Cloud Rats Found in Philippine Cave

Alongside the tiny humans that once inhabited the Philippines lived several hitherto unknown species of giant rats, according to a new study published today in the Journal of Mammalogy. The research broadens our understanding of the twig on the tree of life constituted by these giant cloud rats, showing the rodents had more radiations than previously known.

In terms of the fossil record, Callao Cave on the island of Luzon in the Philippines is probably best known for the discovery of Homo luzonensis, a remarkably short relative of modern humans that lived tens of thousands of years ago. But as the recent finds show, the area was home to a bevy of beasts still waiting to be discovered.

“We were looking at the fossil assemblages associated with that hominin,” said lead author Janine Ochoa, an archaeologist at the University of the Philippines in Diliman, in a Field Museum press release. “And we found teeth and fragments of bone that ended up belonging to these new species of cloud rats.”

The Philippines has a huge concentration of unique mammal species. Earlier this year, on the same island as the recent discovery, a presumed-extinct mouse that hadn’t been seen since the Eisenhower administration turned up in droves, in a habitat that was devastated by a 1991 volcanic eruption. Though the newly described cloud rat species are much less likely to come back from the dead, they help fill a gap in researchers’ understanding of their mammalian tribe, called Phloeomyini, 18 members of which are still around today.

Looking a bit like tree-climbing guinea pigs with long tails, the giant cloud rats are a far cry from the subway and back-alley varieties you find in most cities. They began diversifying on the islands some 10 million years ago, but until now, no extinct fossil species had been described; the three now catalogued from Callao Cave date from 67,000 years ago to the Late Holocene, around 2,000 years ago. Modern members of the group can weigh up to 6 pounds and be nearly 3 feet long from nose to tail. The researchers suspect that the three ancient rodents—Batomys cagayanensis, Carpomys dakal, and Crateromys ballik—inhabited lowland forests, further exemplifying how diverse a portfolio the tribe once boasted; the extant species today live in higher-altitude forests.

“The bigger ones would have looked almost like a woodchuck with a squirrel tail,” said co-author Larry Heaney, the Curator of Mammals at the Field Museum, in the same press release. “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.”

Known only from some 50-odd bone fragments, the new rat species were identified in part thanks to their extraordinarily complex molars, which have a lot of folded enamel for chewing plant matter, like those of cattle. These rats lived when woolly mammoths roamed Earth—which brings us to their demise, which seems to coincide with the first appearances of pottery and stone tools in the archaeological record, as well as the arrival of non-native species to the archipelago, like dogs, monkeys, and the more commonly despised rat, Rattus rattus. 

“Approximately two to three thousand years ago, they disappeared. And the obvious question is, why?” Heaney said. “We know enough now to ask that question. Until we discovered these things, we didn’t know there was a question to be asked.”

The rat bone fragments were found in the same excavation area as the Homo luzonensis bones. As Heaney’s colleague put it, “we didn’t find any empty bottles of barbecue sauce,” so while there’s no obvious evidence that hominins ate the rats, it would make plenty of sense if they did. Different island, same story for a species unfortunate enough to coexist with us, it seems.

More: This monogamous, poisonous rat is full of surprises.