Friday, December 04, 2015

What Killed the Mammoths of Waco?


For two decades, a circus tent stood on the outskirts of Waco, Texas, not far from the point where the Bosque and Brazos rivers converge. But the real elephant attraction was below: Columbian mammoths, still preserved in their death pose, more than 60,000 years after floodwaters left them buried in mud.

The Waco Mammoth National Monument, its circus digs now replaced with a climate-controlled shelter and visitor center, became one of the country’s newest national monuments in July. The first hints of the Ice Age graveyard were discovered by accident in 1978, when two 19-year-olds looking for arrowheads along a dry riverbed found mammoth bones instead. They alerted paleontologists at Baylor University, sparking an excavation that yielded surprisingly rich finds. Within a decade, 16 Columbian mammoths were uncovered and lifted out of the ground in plaster jackets. A second phase revealed six more mammoths, a camel and the tooth of a saber-tooth cat.

The deposit is unique because it preserves a nursery herd—at least six adult females and ten juveniles—that died together in a single event. Unlike the Hot Springs Mammoth Site in South Dakota, where over 60 juvenile and adolescent male Columbian mammoths plummeted to their deaths over the course of many years, the Waco site bears witness to a single, catastrophic event. And the absence of arrowheads and other archaeological remains suggests that the bones aren’t a heap of Paleo-Indian leftovers—this was a mass grave from a natural disaster.

How—and when—did the animals die? New research found a likely answer within the sediments that entombed the creatures. The paper, which was recently published in Quaternary Research, concludes that the original 16 mammoths from the herd were likely standing in the wet, sandy sediment near the confluence of the two rivers when a storm hit. As floodwaters rose, the animals might have been trapped between the river and the ravine’s walls. At 12-to-14 feet tall and weighing seven to eight tons, Columbian mammoths weren’t exactly agile. Perhaps they couldn’t climb the steep slopes to escape in time. Some might have even been trapped in a mudslide. Other mammoths seem to have died in a similar storm while visiting the same area years later.

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