From the outside, Mare aux Songes looks completely harmless—a grassy swampland in the middle of Mauritius, a beautiful island oasis some 500 miles off the coast of Madagascar.
But this wetland is actually home to a subterranean graveyard.
Scientists have deemed it a Lagerstätte, German for “storage space.” That’s because well-preserved fossils litter the vicinity of this one-time lake, which provided the only source of fresh water for native species during an extensive drought that lasted 50 years.
Erik de Boer, a paleoecologist at the University of Amsterdam, wanted to know why the ancient lake—which should have saved these animals—instead became the source of their demise. He and a team of experts reconstructed the history of the island’s ecosystem by analyzing sediments taken from the area today.
They concluded that decreased monsoon activity caused the drought, but at the same time, the lake became increasingly muddy, salty, and, well, poopy. In fact, during the island’s dry season, it was essentially undrinkable. Here’s David Schultz, writing for Science:
“The animals lived around the edges, and the excrements probably got mixed up in the wetlands,” de Boer says. “It’s like a big toilet.” Even worse, the researchers’ analysis shows that the feces-flooded waters encouraged the growth of single-celled algae and bacteria—diatoms and cyanobacteria—which can cause poisonous algal blooms. The circumstances combined to create what the scientists refer to as a “deadly cocktail” that they think killed many of the animals preserved as fossils at Mare aux Songes today.
Fewer animals seemed to have died off in locations where the large lake’s water remained slightly deeper—so thankfully, the dodos and giant tortoises didn’t go extinct. They survived until a greater threat came along in 1638 and hunted them until they were gone.
Photo credit: Via Tsuji / Flickr (CC BY-NC-ND 2.0)