A “bonanza” of remains from extinct giant lemurs has been discovered in a flooded cave in Madagascar, shedding light on the island’s unique ancient megafauna.

Even though people have been finding the giant lemurs’ bones since the 1800s, the team behind the discovery thinks this is the largest find in one place.

“This is really eye-popping,” says from the City University of New York, who led the study. “I’ve never seen anything like this.”

This giant-lemur graveyard lies in a freshwater cave some 42 metres deep in the arid south-western region of Madagascar, which is pocked with dry caves and water-filled sinkholes.

Giant lemurs consist of 17 extinct species that were all bigger than the largest of the 100 or so lemur species living today. The biggest were the size of gorillas.

Rosenberger’s team found “beautifully preserved” remains of two giant lemur species, Pachylemur insignis and Mesopropithecus globiceps. In a nearby cave, they found a rare Megaladapis edwardsi – the largest of the extinct lemurs found in the area – which had a foot-long skull and was similar in size to a female gorilla. It is known as the “koala lemur” because its short limbs evolved for climbing through trees.

The P. insignis skeleton is particularly exciting because, as a fruit-eater, it was one of the largest seed-dispersing lemurs, says , an anthropologist from the University of Massachusetts in Amherst. These lemurs are part of the primate community in Madagascar that has disappeared over the last 1,100 years. Their disappearance may be threatening the survival of plants that depended on them, she says.

Bone menagerie

The researchers also discovered the remains of a horned crocodile, pygmy hippos and gigantic elephant birds, all of which are now extinct.

“The horned crocodile weighed around 170 kg, and was a ferocious predator. There were several species of hippopotamuses in Madagascar, distinct from any known elsewhere,” says Godfrey. “There were around a half-dozen species of elephant birds, all flightless. They looked like gigantic ostriches, and the largest laid eggs the size of 180 chicken eggs.”

Remains of species introduced to the island by humans, like the black rat and Indian civet, were also found in the cave, suggesting that the extinct lemurs were around when the first humans arrived.

It is likely that what can be seen on the surface of the cave floor is just a small fraction of the richness of the sediment-laden deposit, and several thousands of bones may be waiting to be discovered there, the team says.

“The animals deeper in the sediment might be different from the ones we’re finding on top because they may have been laid down at a different time, which could reveal new species. That would be very exciting,” Rosenberger adds.

His hunch is that the deposits in the cave arrived there through flooding. Madagascar is subject to severe cyclones and he thinks there could be an association between these and the time the bones were deposited. Many animals may have died during the storms, been swept in as cadavers and lost their flesh in the cave.

But the exact nature of the flooding and climatic variation preceding it will be better understood when the researchers look at stalagmites and stalactites.

Godfrey says that these only grow in a dry cave – not underwater – so dating the age of the tips of them may pinpoint the time of flooding.

Journal reference: Journal of Human Evolution, DOI:

Our planet’s ice is anything but barren. Upside-down forests cling to the underbelly of polar sea ice, while icebergs are ecological hotspots boosting life in the water around them.

Now, it turns out that glaciers support an unlikely variety of creatures, too, in curious habitats made possible by wind, dust and the sun’s heat.

The surface of a glacier is riddled with holes. Some are needle-thin, others a few metres across, but inside all a secret ecosystem is thriving.

A team of researchers led by , from the Adam Mickiewicz University in Poznań, Poland, has made the first worldwide survey of invertebrates living in these “cryoconite holes”.

They found 25 species, many of which are unique to this habitat. The Arctic is home to 16 of them, with the remainder distributed across Antarctica, the Himalayas, the Americas and the Alps.

The holes occur when windblown dust – cryoconite – settles on the glacier surface. Being darker than the ice, the dust absorbs more heat, resulting in a pool of melted water with a layer of silt at the bottom. The pools are typically around 15 to 20 centimetres deep, and can grow up to several metres in diameter.

Perfect refuge

Like a desert oasis, these sheltered reservoirs provide the perfect refuge for a host of organisms to flourish. Some of these are hardy creatures that arrive on the wind; others seem to be specialised to life in these holes.

“It’s very hard for anything to live within, underneath or on the surface of the glacier, so cryoconite holes are very much hubs of activity,” says , from the Geological Survey of Denmark and Greenland.

The first organisms to colonise the holes are probably windblown arrivals: filamentous cyanobacteria. They are effectively ecosystem engineers, bundling together the dust, soot and organic matter, says of Aberystwyth University, UK. This creates niches that pave the way for fungi, algae and other bacteria, which feed on organic matter. Then along come the top predators, including insect larvae, segmented worms, copepods and microscopic creatures called tardigrades – commonly known as water bears.

“In Arctic regions the big predator is the polar bear, but in cryoconite holes it is the water bear, which feeds on bacteria and algae. They are the toughest organisms on Earth,” says Zawierucha. These organisms survive the long winter by drastically slowing their metabolism and because they probably have antifreeze proteins, which makes them of interest to the pharmaceutical industry (see box below).

Stowaways from afar

They probably first arrived at the glaciers as stowaways on windblown dust, which may come from nearby mountains or tundra, or even from faraway regions such as the Sahara desert, says Cameron.

The holes can also harbour dormant seeds flown in from far away. Last year, at the Centre for Antarctic Plant Ecology and Diversity in Moffat, UK, from spores found in cryoconite holes in Antarctica.

Many of the species endemic to cryoconite holes are black, a finding that surprised Zawierucha. The production of dark pigments probably protects them from high levels of ultraviolet radiation, he says. But it may also help make their environment more habitable.

“The organisms that live in cryoconite strongly control the albedo, or reflectivity, of the holes by attracting more sunlight and, therefore, heating up their world,” says of the University of Derby, UK.

In fact, these organisms are heating up their microhabitats so efficiently that they might be speeding up the melting of the glacier itself.

“This is a significant contributor to glacial surface melt, both on valley glaciers and the Greenland ice sheet,” says Edwards, who calls it “a biological preconditioning of a glacier to its death”.

“It’s a positive feedback mechanism,” says Cameron. “More cryoconite holes increases glacier melt that, in turn, increases the area of snow-free regions, a prerequisite for cryoconite holes. And in a hundred years’ time you’ll probably get more cryoconite holes in glaciers worldwide, and this could contribute to sea level rise.”

What will happen to the invertebrate communities living in these holes as their habitat warms? No one knows for sure. Edwards thinks the species might establish themselves in nearby habitats, such as coastal seas.

Journal reference: