Larry Agenbroad, a paleontologist who presided over the unearthing of scores of fossilized mammoths from a scrape of southwest South Dakota, helping it become an international research destination, died on Oct. 31 in Hot Springs, S.D. He was 81.

His son Brett said the cause was complications of kidney failure.

In 1974, a construction worker clearing land for a housing subdivision on the edge of Hot Springs noticed unusual bones. Dr. Agenbroad, (pronounced AG-in-brawd) a paleontologist and professor at Chadron State College in Nebraska, about an hour away, was called in to study the site.

He initially suspected that the bones could come from at least six mammoths. But after further digging, he concluded that there were as many as 100, trapped more than 26,000 years ago in a sinkhole, whose warm pond, fed by an artesian spring, attracted them with water and vegetation but often would not let them escape. Other scientists helped Dr. Agenbroad determine that all of the mammoths were males and that most were relatively young.

“What is a hungry, newly independent mammoth most likely to do? Use its tusks to sweep three or four feet of snow off last year’s flattened grasses? Or clamber down a steep shale slope and go for the greens?” Dr. Agenbroad wrote in a 1997 article in Natural History magazine.