Elephants in Khao Lak, the hardest hit area in Thailand, trumpeted in fear a full three hours before the earthquake hit Indonesia, hundreds of miles away.
And then sounded the alarm again, before the tidal wave hit more than an hour after the earthquake.
Some were so agitated, they broke their chains and escaped to higher ground.
The elephants gave some kind of notice. They trumpeted the warning. The irony is that it fell on deaf ears: Humans who heard the warnings did not respond, did not understand the danger that was coming.
An elephant handler, Apichart, says it won't happen to him again. Next time, he told Petersen, when the elephants warn, "We'll all run for the hills."
Across the stricken region, many animals sounded warnings, or fled before the tsunami smashed ashore.
On some islands in Thailand, hermit crabs, who live on the beaches, suddenly scampered to higher ground before the wave hit.
At the fishing village of San Souk, birds started a frantic squawking. Villagers took heed and ran, and all 1,000 of them escaped unharmed.
Dive boat leader Chris Cruz saw the sea erupt with scores of dolphins. "I spoke to the captain," he told Petersen. "I rushed up to him and said, 'We have to follow those dolphins.'"
They were led to water so deep, the wave passed harmlessly underneath.
So, says Cruz, the dolphins saved many human lives.
These days, people expect wailing sirens or loudspeaker warnings of coming disasters. There were none. But nature's warnings were there. Had more people heeded them, so many more might have lived.