The dog will soon undergo DNA tests and carbon-dating, authorities say. (Mexico's National Institute…)

MEXICO CITY — For nearly 50 years, the mummified remains of a dog believed to have lived 1,000 years ago sat forgotten in a school museum in north-central Mexico.

That meant, among other things, that no one got to admire the ancient dog's irresistible facial expression.

The canine, which has no name, appears in recently released photographs lying on its side as if relaxing. Its expression is serene and somehow friendly.

Archaeologists say the mummified male dog is about 1,000 years old, but other than that, little is known about it, including whether it is a xoloitzcuintle, the indigenous Mexican hairless dog, because of its curious shape.

The specimen was pulled from the Cave of the Candelaria, a 30-foot-deep ancient burial site in the semidesert region known as La Laguna, by government researchers in 1953. Along with the dog, archaeologists found textiles, ceramics, arrowheads and mummified figures such as a 3-year-old child wrapped in a rope.

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The National Institute of Anthropology and History says

it was eventually stored at the museum of the Escuela de

Bachilleres Venustiano Carranza, a state school in the city

of Torreon.

It lay there, in effect forgotten, until August, when the

institute's archaeologists at the Regional Museum of

La Laguna examined the school's holdings, found

the dog and determined that it hadn't been properly

studied. Authorities said the dog will soon undergo DNA

tests and carbon-dating.

Jaime Alejandro Bautista, the institute's subdirector of

public records, said the mummified remains would prove

telling if they turned out to be those of a xoloitzcuintle

— pronounced "cho-los-kuint-leh." It would push the

border of the breed's native region significantly

farther north than the Mesoamerican region of central

and southern Mexico. It could also suggest that nomadic

northern peoples such as Chichimecas had earlier contact than previously thought with urbanizing pre-Hispanic societies such as the Aztecs.

"We know that dogs are associated with funeral rites in pre-Hispanic societies, so it is likely that it was deposited there intentionally," Bautista said. "The dog mummified naturally, due to the conditions of the microclimate in the cave."

Its skin, or what's left of it, is coated in a varnish, a preservation-minded mistake years ago by an unknown custodian, Bautista said.

"We just lost track of it. At the time, an adequate museum did not exist to receive it," he said.

Indeed, the northern region of Mexico is sorely understudied by anthropologists and archaeologists in comparison with the deeply studied Mesoamerican region. There are even fewer U.S. specialists — "five or six," by one count — who concentrate on the north and who might be able to independently comment on the rare mummified dog.

The dog could be put on display at the Regional Museum of La Laguna as early as mid-2013