In October 2014, in the arid Tsimanampetsotsa National Park, a paleontological team explored Aven Cave, a 25-meter (82 ft) deep flooded sinkhole. Littering the dimly-lit silt cave floor lay several thousands of bones from dozens of species. The species ranged from the extinct elephant bird and horned crocodile to the still-living leaf-nosed bat. Thousands more remains could still be hiding underneath the cave floor.
These animals were unlikely to have visited or lived in the cave, so researchers aren’t certain how all these partially fossilized bones also known as subfossils got into the sinkhole. It is likely that water could have washed the animal remains from the surface into the formerly dry cave, evident by the presence of stalagmites and stalactites.
According to Alfred Rosenberger, the anthropologist and archaeologist who led the expedition, “sinkholes can often provide unprecedented views into the past.” The cave’s isolation and cold water protect the bones from “the ravages of bacteria, wind, and waves,” leaving “skulls and jaws virtually complete and, very often, even undamaged” – a rarity in mammal paleontology.