Anthropologists have found skeletons of at least 14 woolly mammoths that died after falling into traps built by humans 15,000 years ago.
The two pits were found in Tultepec, just north of Mexico City, Mexico's National Institute of Anthropology and History said this week.
Researchers speculated that ancient hunters probably chased the giant animals into the pits, which are 1.70 meters deep and 25 meters in diameter (5½ feet by 82 feet).
There was some evidence that some of the mammals had been butchered.
Luis Cordoba, the head of the excavation team, said the discovery was key in studying the relationship between prehistoric hunting and gathering communities and the huge herbivores.
"There was little evidence before that hunters attacked mammoths. It was thought they frightened them into getting stuck in swamps and then waited for them to die," he told reporters. "This is evidence of direct attacks on mammoths. In Tultepec we can see there was the intention to hunt and make use of the mammoths."
The pits were found when crews were digging in the area to build a garbage dump.