An artist's model of the Montana Dueling Dinosaurs based on geographical placement of the fossils.
The Dueling Dinosaurs are billed as the most complete dinosaur skeletons ever found in the Hell Creek Formation in Montana. Shown here is the snout of a theropod, thought by some to represent a Nanotyrannus lancensis.
The theropod in the Dueling Dinosaurs group lies encased in its field jacket. Scientists have debated whether specimens dubbed Nanotyrannus actually represent members of a distinct species or simply juvenile versions of T. rex.
Clayton Phipps, also known as the Dinosaur Cowboy, excavated the fossils up for auction at Bonhams.
Some of the coarse skin of the ceratopsid is preserved on the fossil.
The fossils' sellers say the ceratopsid (its foot is shown here) could represent a new species of Triceratops or early Triceratops horridus.