Scientists believe they’ve uncovered the true story behind why woolly mammoths died out, and it’s a bizarre tale of a species’ last stand that left the animals looking much different than what they were doing their peak years. Researchers analyzed ancient DNA of the extinct mammals, specifically looking for mutations, and they found that their genetics were completely messed up at the very end.

The mammoths were so affected by genetic disease that they no longer had a sense of smell, they avoided other mammoths, and they even had a shiny coat. It’s a big discovery that could lead to a better understanding of this mysterious species, and perhaps to better conservation efforts for the species that are threatened today, according to the paper.

Scientists estimate that there were only a few hundred or so woolly mammoths living on Wrangle Island in the Arctic Ocean about 4,000 years ago, and the species was falling apart before it went totally extinct.

“There is a long history of theoretical work about how genomes might change in small populations. Here we got a rare chance to look at snapshots of genomes ‘before’ and ‘after’ a population decline in a single species,” said Rebekah Rogers, who led the work as a postdoctoral scholar at Berkeley and is now an assistant professor at the University of North Carolina at Charlotte, in a statement on the university’s website. “The results we found were consistent with this theory that had been discussed for decades.”

Scientists published the study in the journal PLOS Genetics.

“We found an excess of what looked like bad mutations in the mammoth from Wrangel Island,” Rogers said. “With only two specimens to look at, these mathematical models were important to show that the differences between the two mammoths are too extreme to be explained by other factors.”