NEW YORK — It started with a dinosaur pelvis protruding through the rock at a Montana ranch. Three more months of chiseling and digging revealed a remarkable discovery: two nearly complete, fossilized dinosaur skeletons of a carnivore and herbivore, their tails touching.

A pushed-in skull and teeth of one dinosaur embedded in the other suggested a mortal confrontation between them.

Clayton Phipps, a fossil hunter who made the discovery on his neighbor’s land in 2006 in the fossil-rich Hell Creek Formation, dubbed them the “Montana Dueling Dinosaurs.”

Phipps and the ranch owners have put them up for sale at Bonhams auction house on Tuesday for an estimated $7 million to $9 million, a price out of the reach of most museums.

The auction record for a dinosaur fossil is slightly more than $8.36 million, which was set in October 1997 for a Tyrannosaurus rex skeleton that sold at Sotheby’s. Known as Sue, the skeleton is on display at The Field Museum in Chicago.

The fossils are believed to be a Nanotyrannus lancensis, a smaller relative of the T. rex, and a newly discovered species of Chasmosaurine ceratopsian, a close relative of the Triceratops, which lived at the end of the Cretaceous age some 65 million years ago.

“I am just the lucky guy that happened to stumble out there and find this dinosaur,” Phipps said. “I really appreciate the academic paleontologists that understand the importance of what us amateurs bring to the mix. I am hoping that it will be professionally and academically studied. … I want to know more about them.”