“Giant Cloud Rat” fossils discovered in Philippine caves
Fluffy rodents twice the size of a gray squirrel survived for tens of thousands of years, then abruptly vanished a few thousand years ago – possibly driven to extinction by humans.
Rats, on the whole, are not very popular animals. But while you don’t want an infestation of common black rats living in your home, their distant cousins from the Philippines are downright cuddly. These “giant cloud rats” live in the treetops of misty mountain forests, and they fulfill an ecological role occupied by squirrels in the United States. And, it turns out we have new evidence that they have lived in the Philippines for a long time – scientists have discovered the fossils of three new species of giant cloud rats that lived alongside ancient humans.
“Our previous studies have shown that the Philippines has the greatest concentration of unique mammal species of any country, most of which are small animals, less than half a pound, that live in the rainforest,” Larry Heaney, the Neguanee curator of Mammals at the Field Museum in Chicago and author of a study in the Mammalogy Journal describing the new species. “These recently extinct fossil species not only show that biodiversity was even greater in the very recent past, but that the two that went extinct just a few thousand years ago were giants among rodents, both weighing more. of two pounds. Their abrupt demise just a few thousand years ago makes us wonder if they were big enough to be worth hunting and eating.
“We have had evidence of large mammals extinct on the Philippine island of Luzon for a long time, but there is virtually no information on the fossils of smaller mammals. The reason is probably that the research has focused on outdoor sites where large fossil mammal faunas were known to have been preserved, rather than the careful sifting of cave deposits which preserve a wider range of sizes. vertebrates, including rodent teeth and bones. Says Janine Ochoa, assistant professor of archeology at the University of the Philippines – Diliman and lead author of the study.
At the start of the study, Ochoa was examining the fossil assemblages in the caves of the Callao limestone formation, where a few years ago scientists discovered the remains of an ancient human species, Homo luzonensis. “We looked at the fossil assemblages associated with this hominin, and we found teeth and bone fragments that ended up belonging to these new species of cloud rats,” Ochoa explains.
The fossil fragments uncovered by the Callao Cave excavation team are not the only traces of cloud rats, however – they may have added other fossils in the collections of the National Museum of the Philippines. “Some of these fossils were actually unearthed decades ago, in the 1970s and 1980s, and they were in the museum, waiting for someone to have time to do a detailed study. When we started to analyze the fossil material, we expected fossil records of known living species. To our surprise, we found that we were not dealing with one, but three species of giant cloud rats that were previously unknown, ”said Marian Reyes, zooarchaeologist at the National Museum of the Philippines, one of the authors of the study.
However, the researchers didn’t have a ton of materials to work on – just fifty or so fragments. “Normally when we look at assemblages of fossils, we are dealing with thousands and thousands of fragments before you find something rare and really nice,” Ochoa explains. “It’s crazy that in these fifty fragments, we found three new species that had not been recorded before.
The fragments the researchers found were mostly teeth, which are coated with a hard enamel substance that makes them stronger than bones. However, from a few dozen teeth and pieces of bone, the researchers were able to put together a picture of what these animals looked like in life, thanks, in Heaney’s words, to “days, days and days. days to look at under a microscope ”.
By comparing the fossils to the 18 living species of giant cloud rats, the researchers get a good idea of what these three new fossil species would have looked like.
“The bigger ones almost looked like a groundhog with a squirrel tail,” Heaney says. “Cloud rats eat plants, and they have very big bellies that allow them to ferment the plants they eat, much like cows. They have large, fluffy or hairy tails. They are really very cute.
The newly recorded fossil species came from Callao Cave, where Homo luzonensis was discovered in 2019, and several smaller caves adjacent to Penablanca, Cagayan province. Some specimens of the three new fossil rodents have occurred in the same deep layer of the cave where Homo luzonensis was found, dated to around 67,000 years ago. One of the newer fossil rodents is known from only two specimens of this ancient layer, but the other two are represented by specimens from this early date until about 2000 years ago or later, meaning that ‘they were resilient and persistent for at least 60,000 years. “Our records show that these giant rodents were able to survive the profound climate changes from the Ice Age to the present-day humid tropics that have impacted the earth for tens of millennia. The question is, what could have caused their final extinction? Adds Philip Piper, co-author based at Australian National University.
Two of these giant rodents apparently went extinct about two thousand years ago, or soon after. “This seems significant, as it was around the same time that Neolithic pottery and stone tools first appeared in archaeological records, and when dogs, domestic pigs and possibly monkeys were introduced. in the Philippines, probably from Borneo. While we can’t say for sure based on our current information, it does imply that humans likely played a role in their extinction, ”says Armand Mijares, professor in the archaeological studies program at the University of the Philippines – Diliman, who led the excavation. from the cave of Callao.
“Our findings suggest that future studies that specifically look for small mammal fossils can be very productive and can tell us a lot about how environmental changes and human activities have impacted the truly exceptionally distinctive biodiversity of the Philippines.” , according to Ochoa. And such studies can also tell us a lot about the impact of human activities, perhaps specifically hunting, on biodiversity, Heaney notes. “This is something we need to understand if we are to be effective in preventing extinction in the future.”
Reference: “Three New Species Extinct from Endemic Radiation of Philippine Cloud Rats (Rodentia, Muridae, Phloeomyini)” by Janine Ochoa, Armand SB Mijares, Philip J Piper, Marian C Reyes and Lawrence R Heaney, April 23, 2021, Mammalogy Journal.
DOI: 10.1093 / jmammal / gyab023