Nine-year-old Jude Sparks was playing with his brother in the New Mexican desert when he tripped and landed beside a massive skull.

"I didn't know what it was," Sparks, now aged 10, told El Paso ABC affiliate KVIA. "I just knew it wasn't usual."

Sparks later found out he stumbled upon an archaeological treasure: a mostly intact stegomastodon skull.

At the time of the discovery, neither Sparks nor his parents, who were biking nearby, recognized the skeletal remains of the million-year-old creature preserved in the desert sands of Las Cruces.

Sparks' parents took a photo of the skull, presuming it belonged to an elephant, and went to work googling. When their internet search provided no definitive answers, they emailed Peter Houde, a biology professor at New Mexico State University (NMSU).

A day after Sparks' fortuitous stumble, Houde headed out with the family to take a closer look and confirmed that the skull "is really very unusual to find," he revealed in an interview with the New York Times.

According to the newspaper, prehistoric fossils usually break down after exposure to the elements, but the Sparks were fortunate to have discovered the skull just after strong rains made it visible to the naked eye.

"Erosion is a paleontologist's best friend," Spencer Lucas, curator of paleontology at the new Mexico Museum of Natural History and Science, explained to National Geographic.

This May, after months devoted to securing funding and planning, the Sparks family and a university team excavated the nearly 2,000-pound fossil. Houde estimates the skull to be about 1.2-million-years-old. He believes it is one of only hundreds of stegomastodon fossils unearthed globally.

"This may be only the second complete skull found in New Mexico," the biologist explained in the university's statement.

Although its name might suggest otherwise, stegomastodons are not dinosaurs. The elephant-like creature walked the earth in the last million years or so, reports the Times, and dinosaurs died close to 66 million years ago.

Sparks told the Times that he went through a fossil phase in his earlier years, and discovering the skull has reinvigorated his interest in archaeology. Nonetheless, it hasn't given him much credit with friends on the playground.

"Most of them didn't even believe me," Jude told KVIA.

Houde, however, doesn't encourage citizen scientists to take to the desert in search of fossils.

"When people find out about these things, they might be tempted to go out there and see what they might find themselves," Houde said in the university press release. "To be quite honest, all these fossils from this area are radioactive and especially for children, not something you would want in your home."

Read Michelle Robertson’s latest stories and send her news tips at mrobertson@sfchronicle.com.