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Triceratops and Pachycephalosaurus Skulls

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Triceratops and PachycephalosaurusThese late Cretaceous (about 70 million years old) dinosaurs were found in 1994 on a Sierra College paleontological field trip. They are from the Hell Creek Formation at Fort Peck Reservoir in Montana. This is the same area where skeletons of Tyrannosaurus rex have been found.


The Pachycephalosaurus skull is probably the largest of its kind found. Originally when this specimen was found by Frank DeCourten it was mistaken for a ball joint of a dinosaur femur. Upon going back to the site a year later, the "femur" was actually the back half of a skull with a missing eye socket. Although another field trip was taken to the area the following summer, the nose or any other portions of the skull could not be found. The nose portion was later sculpted by artist Ken Kirkland.

Pachycephalosaurus skullPachycephalosaurus was a bipedal herbivore with strong hind limbs and smaller "arms" with grasping hands. Its name means thick-headed reptile. The domed portion of the skull can be as much as 10 inches thick.

The Story of the Skull

While looking for dinosaur skulls in Sand Hollow north of our campsite at Fort Peck Reservoir in Eastern Montana, Frank DeCourten found what appeared to be the ball of a femur from a large dinosaur, probably a Triceratops. It was in a slump that had slid off the side of a low hill. Without the rest of the bone it didn’t seem worth the time to collect and thus reduce our efforts at finding a skull.

While the medium size Triceratops skull was being excavated, Charles Dailey decided it would be useful for a scaling activity for his zoology lab. He left the excavation crew and went back and collected the femur ball. It sat in the lab for a long time while the skull was being prepared. A student volunteered to remove the jacket and prepare the femur ball. While doing so the student noticed a series of bumps around one edge that did not match the sample femur provided for comparison.

When Dick Hilton looked at it he recognized that it was the rear part of a skull of a large, bipedal Pachycephalosaurus dinosaur. It turned out to be the largest one ever found. Some people had speculated that they used their thick skullcap as a battering ram, like bighorn sheep rams. Mark Goodwin of U.C. Berkeley’s Museum of Paleontology is the world’s authority on this group of dinosaurs. He asked to borrow and study it. X-rays and CAT scans did not reveal enough detail. Mark asked for permission to saw the skull in half to study the internal structure in detail. When he explained why Hilton gave permission. A poster detailing the deconstruction and reconstruction of the skull is on display in the northeast foyer.

The results suggested that the joints in the skull never became strong enough to allow head to head butting. However they may have used heads to bang each other in the neck or rib cage as do male giraffes in mating bouts.

Other smaller skull parts with similar rear spikey projections were found in the area. They are on display in the floor case They have been named Stegoceros (not the same as the larger quadrupedal Stegosaurus) and Stigimoloch. Researchers have finally decided that these are just younger versions of the larger forms that were called Pachycephalosaurus.


Triceratops occipital condyleThe Triceratops skull was found by students Jeanine Ingram and Janet Olson at Fort Peck Reservoir in eastern Montana when they found the tip of a Triceratops horn poking out of the bank. It was part of a nearly complete medium size skull, an incomplete skull of this horned dinosaur. The skull is torqued out of shape from the pressure of burial. Triceratops is the largest of the horned dinosaurs.

Like most other herbivores, including modern bison and rhinoceros, it may have traveled in herds and used its horns for protection. Only the right one-third of the frill was preserved. It was found crushed under the main portion of the skull. The occipital condyle was also found. This is the ball joint that connects to the vertebral column. The nose portion was missing. The nose portion on display was sculpted by artist Ken Kirkland.

On a return trip Dick Hilton found the skull of a juvenile. It was munched by the sediment into almost gravel. Dick Hilton spend months at this kitchen counter assembling parts. Only one smaller juvenile skull has been found. It is about the size of the skull of a bull of a large variety of cattle. Because the first find of this kind of dinosaur was bull size it was named Torosaurus (Bull lizard). Later when a series of sizes of skulls were found it was discovered that Torosaurus was just the juvenile form of what was later named Triceratops. The original of our juvenile is on display as part of such a series at the Museum of the Rockies in Bozeman, Montana. A replica of the juvenile will be on display soon in our museum.

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