A team led by National Geographic fellow and Brooklyn College professor Alfred Rosenberger found three flooded caves in Tsimanampesotse National Park, each containing an unprecedented number of large, perfectly preserved specimens. One in particular, Aven Cave, is so packed with bones that divers felt them every time they put their hands down.
“It’s just phenomenal,” researcher Laurie Godfrey, a paleontologist at the University of Massachusetts at Amherst, said in a phone interview with The Washington Post. “A huge cache of fossils like this has never been explored before. Now that we know that it’s there, it’s opening up a new era in paleontological exploration.”
The researchers’ most prized findings are the bones of several extinct species of giant lemurs, ranging from several hundred to several thousands of years old. Among them are specimens of Megaladapis, a big-nosed, beady-eyed creature whose heavy, squat body more closely resembled a koala’s than those of the diminutive lemurs we know today, and Archaeoindris, the largest known lemur species that was the same size and weight as a gorilla.
The discovery, which National Geographic announced Tuesday, is just the first step in what Godfrey hopes will be a more thorough investigation of the caves. The initial sweep brought up so many fossils that researchers haven’t even begun to dig into the sediments on the cave floors. Once they do, Godfrey estimates they’ll find thousands of specimens from dozens of extinct species.
The caves remained unexplored for so long because of the difficulty of probing their flooded interiors. In Aven Cave, where the fossils were most abundant, the water is 130 feet deep and often murky.
But that same water is also what makes the caves such perfect places to find fossils.
“In a flooded cave the preservation can be just marvelous,” Godfrey said. “Nothing’s bothering them, nothing’s disturbing them.”
The quality of the fossils will be key for scientists’ research into the causes of the animals’ disappearance. Godfrey said that researchers will likely be able to obtain DNA samples from the specimens, carbon date them to see when they died, and examine them for cut marks or other signs of human butchering.
“All of this information can help us flesh out the story that we’re telling about what happened to the giant lemurs and the associated fauna,” she said.
It’s long been understood that human arrival on Madagascar about 2,000 years ago coincided with the sudden die-off of much of the island’s wildlife. Two-thirds of the species that lived on the island a millennium ago are now extinct, in part because of changes caused by humans, Godfrey said. What’s not clear is exactly how those changes led to the animals’ demise.
“You’re dealing with a situation where not only are humans coming but they’re bringing a lot of other animals and plants that transform the habitat. They’re hunting,” for example, she said, and “it could be that certain species didn’t want to come near water or food sources because humans were around. There’s competition with new introduced species. There’s a number of long, complicated stories people have put forth as to why these animals are extinct.”
Untangling those stories isn’t just a matter of understanding history — it can help with conservation efforts today. Lemurs are the most threatened mammal species on Earth, according to a policy paper published last year in the journal Science, and Madagascar is the only place where they are found in the wild.
“It’s a very sad situation in Madagascar. The threat to species is tremendous, there’s a high rate of extinction,” Rosenberger said in a video for National Geographic. “We’d like to know what the interaction was between people, climate change, habitat change … that contributed to the demise of the giant lemurs. Because knowing that might give us some perspective on what we have to prepare for the future.”