A mysterious ancient stone mask from Mexico has spoken — but apparently only to say that its people's written language remains undeciphered.

A study by Brigham Young University archaeologist Stephen Houston and his colleague from Yale University, Michael D. Coe, say the mask disproves earlier claims that the language had been cracked.

Their paper is to be published in "Mexicon," a journal about news and research from Mesoamerica. The title is "Has Isthmian Writing Been Deciphered?"

The "Teo Mask" may be about 1,600 to 1,900 years old. It was carved in a hard, greenish stone. The inside surface is covered with mysterious hieroglyphs.

In 1993, two researchers — John S. Justeson of the State University of New York, Albany, and Terrence Kaufman of the University of Pittsburgh, both anthropology professors — claimed in the journal Science that they had deciphered that written language.

Kaufman and Justeson call the writing "epi-Olmec script." However, Houston and Coe term it "Isthmian" because it was written by people who lived on and around Mexico's Isthmus of Tehuantepec. They date to within five centuries before and after A.D. 1.

Kaufman and Justeson said they had deciphered the writings based on semantic clues associated with known cultural practices and a similarity of the hieroglyphs to other writings in the region that had been deciphered.

They claimed to be able to read the earliest writings known from North America, inscriptions on large stone carvings called stela found in Veracruz, Mexico. The dates on the stones, they added, were A.D. 159 and A.D. 162.

The announcement made international headlines. But Houston and Coe doubt anyone can read the script.

Houston, an anthropology professor who is an expert on ancient Mesoamerica, won a John Simon Guggenheim Memorial Fellowship in 2002. When he attended Yale, he was a student of Coe's.

Coe, a retired anthropology professor from Yale, was author of the 1992 book, "Breaking the Maya Code." The book details the work of Coe and colleagues in deciphering the written Mayan language. Houston had a role in that effort.

They write in their new paper that Justeson and Kaufman are respected scholars, but they disagree that the writings have been deciphered.

The writing is "immensely complex. That is, it's very well developed with a large number of signs," Houston told the Deseret Morning News.

If it really were readable, he said, "it would open the window to a big chunk of the past."