A Sinkhole at Least 20 Meters Deep in South Dakota May Have Been Too Slippery and Steep for Mammoths to Escape 190,000 Years Ago.
During a construction project in the Black Hills region of South Dakota in 1974, a bulldozer operator discovered a massive mammoth tusk. Scientists later found that a large number of mammoths had perished in this death pit, which is deep enough to contain a four-story building.
Scientists have excavated about 8 meters deep, which is less than half the depth of the sinkhole. (Photo: Jesse Brown Nelson/The Mammoth Site)
In the late 1970s, paleontologist Larry Agenbroad requested the construction of a building to protect the area, called the Mammoth Site. He spent decades excavating mammoth fossils from the pit until his passing in 2014.
Today, the sinkhole in South Dakota is a valuable treasure for paleontologists, providing a rare glimpse into the distant past. Over the past half-century, they have discovered fossils of 61 mammoths and many other ancient creatures, even though they have yet to reach the bottom of the pit.
The Black Hills area of South Dakota is prone to sinkholes, according to Chris Jass, research director at the Mammoth Site Museum. Essentially, groundwater erodes the surrounding area, creating underground caves. “Eventually, those caves grow to a size that cannot support the weight above and collapse,” he said.
The death pit at the Mammoth Site measures 46 x 37 meters and is at least 20 meters deep. The walls of the pit are made of Spearfish shale, which is extremely slippery. Mammoths weighing up to 10 tons likely fell in and could not climb out of this steep and treacherous hole.
There are two types of mammoths found in the sinkhole: the woolly mammoth and its larger, less hairy relative, the Columbian mammoth. South Dakota is slightly south of the woolly mammoth’s range, so the majority of the fossils found in the pit are Columbian mammoths. The fossils are dated to between 140,000 and 190,000 years old.
To date, scientists have discovered over 60 mammoths. (Photo: The Mammoth Site)
The Mammoth Site sinkhole helps researchers understand more about the behavior of mammoths, particularly the behavior of young males. Modern elephant herds are matriarchal, mainly consisting of females and young. Mammoths were similar.
“When young male mammoths reach sexual maturity, they are ‘kicked’ out of the herd and must fend for themselves or form groups with other male mammoths,” Jass explained. This may be why all the skeletons found in the sinkhole are male, primarily aged 12 to 28 years.
This also suggests that they did not all die trapped in a single catastrophic event. If that were the case, the pit would contain both males and females of varying ages.
Many mammoth skeletons are not complete, and mammoths were not the only creatures trapped in the pit. Archaeologists have discovered many fossil fragments of wolves, coyotes, camels, extinct camels, and even the nearly complete skeleton of a giant short-faced bear.
However, there is a reason mammoths make up the majority of the fossils in the pit. <strong“Some smaller animals are a bit more agile,” Jass noted. He mentioned that even the short-faced bear is a surprise because it could have climbed out unless it was injured. However, it is also possible that floods washed bones into the pit, while smaller animals were not trapped.
It is likely that dozens of mammoths are still waiting to be excavated in the sinkhole. Constructing a building around this area helps protect them from the elements, allowing archaeologists more time to search. Jass estimates that the sinkhole contains a total of about 100 mammoths. “Perhaps by the end of my life, they still won’t be fully excavated, but I estimate that we will eventually reach that number,” he said.
