Workers have discovered hundreds of bones belonging to Ice Age animals, including mammoths, mastodons and glyptodons, while digging to build a wastewater treatment plant north of Mexico City.

The bones could be between 10,000 and 12,000 years old and may include a human tooth from the late Pleistocene period, Mexico’s National Institute of Anthropology and History said Thursday.

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Tusks, skulls, jawbones, horns, ribs, vertebrae and shells were discovered 20 meters (65 feet) deep in Atotonilco de Tula, a town in the state of Hidalgo, as workers built a drain, the institute said.

These remains belong to a range of species including mastodons, mammoths, camels, horses, deer and glyptodons, the armadillo’s ancestor. Some bones may belong to bison, while others have not been identified.

Archeologists have worked for the past five months to recover the bones.

“It is the largest and most varied discovery of extinct megafauna found together in the Mexico basin,” archeologist Alicia Bonfil Olivera said in a statement.

An anthropologist will have to confirm whether the tooth belonged to a human.

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“It is not strange because we know that man already lived in the central Mexico region during that period,” the archeologist added.