The sinkhole where 100 mammoths died

During a construction project in the Black Hills of South Dakota in 1974, a bulldozer operator discovered a giant mammoth tusk. Scientists later discovered that a large number of mammoths had perished in the sinkhole, which was deep enough to accommodate a four-story building.

In the late 1970s, paleontologist Larry Agenbroad requested the construction of a building to protect the area, which he called the Mammoth Site. He spent decades excavating mammoth fossils in the pit until his death in 2014.

Today, the South Dakota sinkhole is a treasure trove for paleontologists, offering a rare glimpse into the ancient past. Over the past half century, they have found fossils of 61 mammoths and many other ancient creatures, although they have not even dug to the bottom of the pit.

The Black Hills region of South Dakota is prone to sinkholes, according to Chris Jass, director of research at the Mammoth Site Museum. Basically, groundwater erodes the surrounding area, creating underground caves. “Eventually, those caves grow to a size that can no longer support the weight above them and collapse,” he said.

The sinkhole at Mammoth Site measures 46 x 37 m and is at least 20 m deep. The pit walls are made of Spearfish shale, which is extremely slippery. The 10-ton mammoths would have likely fallen in and been unable to climb out of the dangerously steep and slippery pit.

There are two types of mammoths in the sinkhole: woolly mammoths and their larger, less hairy cousins, the Columbian mammoths. South Dakota is located a bit south of the woolly mammoth’s range, so the majority of fossils in the pit are Columbian mammoths. The fossils are 140,000 – 190,000 years old.

sinkhole Mammoth Site help researchers understand more about mammoth behavior, especially the behavior of young males. Modern elephant herds are matriarchal, consisting mainly of females and their young. Mammoths were similar.

“When young male mammoths reach sexual maturity, they are ‘kicked’ out of the herd and are left to fend for themselves or form groups with other male mammoths,” Jass said. That may be why all the skeletons in the sinkhole were males, mostly 12 – 28 years old.

This also suggests that they were not all trapped in a single catastrophic event. If so, there would have been both males and females of a wider age range in the pit.

Many of the mammoth skeletons were incomplete, and mammoths weren’t the only creatures trapped in the pits. Archaeologists have found fossilized remains of extinct wolves, coyotes, llamas, camels, and even the nearly complete skeleton of a giant short-faced bear.

But there’s a reason why mammoths make up the majority of the fossils in the pit. “Some of the smaller animals are a little more mobile,” Jass says. Even the short-faced bear is a surprise, he says, because it would have been able to climb out unless it was injured. However, it is also possible that flooding washed the bones into the pit, and the small animals were not trapped.

It is likely that dozens of mammoths are still waiting to be excavated in the sinkhole. Building around the area has protected them from the elements, allowing archaeologists more time to search. Jass estimates that the sinkhole contains a total of about 100 mammoths. “It probably won’t be all excavated in my lifetime, but I estimate that it will eventually reach that number,” he said.