The tooth was found by Allison Dodd while she was searching for fossils in Waters Creek at the Day Spring Nature Preserve with her mother and father supervising, the Dallas Morning News reported Friday.

"We thought it might have been a big fish's rib cage or something like that," the girl said of the foot-long object.

The family brought the mystery object to the Heard Natural Science Museum and Wildlife Sanctuary in McKinney, Texas. They showed their find to collections curator Roger Sanderson.

"He kind of grinned when he saw it," said Mark Dodd, Allison's father. "And he showed us a smaller version of a similar-looking thing."

Dodd said Sanderson had the object confirmed as a mammoth tooth.

"Elephants are my favorite animal," Allison Dodd said proudly. "Elephants and mammoths are in the same group."

The girl said she plans to keep the tooth, despite offers from collectors.