Cristina Garcia/INAH

Archaeologists in Mexico have uncovered 25 "alien"-looking human skulls with in a cemetery in the northwest state of Sonora, they said today.

Some of the skulls showed "deformities," said Cristina Garcia Moreno, who worked on the excavation project with Arizona State University, which analyzed the bones. The bones are about 1,000 years old, dating from 945 A.D. to 1308 A.D.

"This was an Hispanic cemetery with 25 skulls, and 13 of them have deformed heads," Moreno told ABC News today. "We don't know why this population specifically deformed their heads."

Moreno said that scientists had found skulls in other parts of Mexico, including Guasave, south of Sonora that also showed similar deformities in certain groups of people. Scientists believe they put beams of wood on the front and back of individuals' heads and wrapped the wood with bands to exert pressure on the skull, Moreno said.

"We know that in some parts of Mexico, people deformed their heads because they wanted to distinguish important people or they wanted to distinguish people from one group from another," she said.

Moreno said that skulls like this had never before been found in Sonora, and that many of the skeletons in the cemetery were those of children.