Specimen:  RMDRC "Sandy" (cast)

Discovery:  Mike Triebold, 1994

Excavated:  Harding County, SD

Length:  9.8 ft

Height:  3.9 ft

Weight:  est. 800 lbs

Skull dome:  4 inches thick

While excavating the Sandy Site in northwestern South Dakota during the summer of 1994, Mike Triebold and his team discovered the first ever Pachycephalosaurus specimen with both a skull and partial skeleton. Along with  paleontologist Dr. Dale Russell, the fossil (nicknamed "Sandy") was analyzed and found to be the most intact specimen at more than 50% complete and with all areas of the skeleton represented.

The skull was more than 65% complete, including the first ever discovered lower jaw, and was the first found with significant neck vertebrae. The "U" or "S" curve shape and "dainty" bones of the neck suggest these creatures could not head-butt as popularly portrayed. However, injuries such as puncture holes in the thick skulls of multiple specimens support a flank-butting in which the spikes were used for attack while the skull dome (up to 10 inches thick) served as protection, though it is still a matter of research and debate. The original specimen now resides at the National Museum of Nature and Science in Tokyo, Japan.