Bargain, 1.7" Pachycephalosaurus Caudal Vertebra - Montana
This is a 1.7" caudal (tail) vertebra of a Pachycephalosaurus ("thick headed lizard") from the Hell Creek Formation, Glendive, Montana.
Pachycephalosaurus was a bipedal dinosaur that lived during the Late Cretaceous period and probably was about 15 feet in length.
Pachycephalosaurus had a distinctive, large, bony, dome on top of it's skull up to 10 inches thick to cushion it's brain from impacts.
Some paleontologists believe this thick skull may have been used for head-butting, much like rams while others contend it may have been a sexual display.
It was one of the last non-avian dinosaurs before the K-T extinction event, 65 million years ago.
There is only one known species of Pachycephalosaurus, Pachycephalosaurus wyomingensis. It's remains have been found in Montana, South Dakota and Wyoming.
It was either a herbivore or an omnivore with small leaf shaped teeth which would have been very effective at shredding plants.