Genus: Pachycephalosaurus BROWN & SCHLAIKJER, 1943 (nomen conservandum)
Etymology: Greek, pachys, “thick”, Greek, kephale, “head” and Greek, sauros, “lizard”: “thick-headed lizard”.
= Pachycephalosantus SANZ, 1990 (sic)
= Tylosteus LEIDY, 1872 (nomen oblitum)
Etymology: Greek, tyle, “swelling, knob” and Greek, osteon, “bone” + us: “knob-boned one”.

Species: wyomingensis (GILMORE, 1931) BROWN & SCHLAIKJER, 1943
Etymology: In reference to the state of Wyoming, where the type was found.
= Troodon wyomingensis GILMORE, 1931
= Stegoceras wyomingense (GILMORE, 1931) KUHN, 1964
= Stegoceras wyomingensis (GILMORE, 1931) KUHN, 1964

Holotype: USNM 12031

Locality: 9 miles (14.25 km) southwest of Warren Post Office on Bug Creek, Niobrara County, Wyoming.

Horizon: Lance Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material: A well-preserved, fragmentary, frontoparietal area with squamosals and part of the occipital region and endocast.

Referred material:

Locality: Niobrara County, Wyoming.

Horizon: Lance Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

USNM 7806: Two incomplete bone fragments.

 


Locality: Seven Mile Creek, Niobrara County, Wyoming.

Horizon: Lance Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

USNM No. 8295: A fragment of the posterior corner of the squamosal.

 


Locality: Unknown, Niobrara County, Wyoming.

Horizon: Lance Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

CM 3180: Greater portion of the dome-like part of skull.

 


Locality: Sec. 25, T20N, R21E, Corson County, South Dakota.

Horizon: Probably Hell Creek Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

Colo. Mus. No. 470: Portion of the frontoparetial area.

 

GALTON & SUES, 1983

Locality: 25 miles (40 km) above the mouth of Lance Creek, Niobrara County, Wyoming.

Horizon: Lance Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

YPM 272: A right squamosal.

 


GIFFIN, 1989

Locality: T1S, R55E, west side of Dry Creek Road, 0.2 miles (.l32km) north of its intersection with Powder River [sic. Powderville] road, Carter County, Montana.

Horizon: Hell Creek Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

USNM 264304: Fragmentary skull cap.

 

Locality: Western Carter County, Montana.

Horizon: Hell Creek Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

CCM 87.1: Juvenile skull cap.

 


Locality:

Horizon:

Biostratigraphy:

Age:

Material:

DMNH 469, SDSM 54204: Juvenile skull caps.

UCM 42763: Fragmentary skullcap.

 

GOODWIN, 1989

Locality: Garfield County, Montana.

Horizon: Hell Creek Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

UCMP 131334: A broad-domed Skull.

 

GOODWIN & EVANS, 2016

Locality: NCD01 locality, Garfield County, Montana.

Horizon: Hell Creek Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

ROM 53671: Incomplet right jugal missing only the anterior (suborital) ramus and parietal.

ROM 53672: Almost complete parietal missing only the ventral flanges that contact the supraoccipital, squamosal.

ORM 53665: Incomplete left squamosal consisting of the lateral and postrolateral regions of the bone with a complete set of ornimation, missing the vetnral and medial rami. Note: found approximately 0.6 km east of NCD01.

 

JACOBSON & SROKA, 1998

Locality: A private ranch in Corson County, South Dakota.

Horizon: Hell Creek Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

Number: Not given: At least 9 specimens, a juvenile frontoparietal and a partial skull.

 

PETERSON & VITTORE, 2012

Locality: Exact coordinates of the collection site are on file at the Burpe Museum of Natural History (BMR), Carter County, Montana.

Horizon: Hell Creek Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

BMR P2001.4.5: Isolated frontoparietal dome with two large oval depressions on the dorsal surface, accompanied by numerous circular pits on teh margin and inner surface of the larger depressions possible due to head butting.


STEPHENSON, 1997

Locality: South Dakota.

Horizon: Hell Creek Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

Number: Not given: Fragmentary skull.

 


= Tylosteus ornatus LEIDY, 1872 (nomen oblitum)
Etymology: Latin, ornatus, "ornamented/decorated."

Holotype: ANSP 8568

Locality: Unknown, "on a low ridge between the Little Missouri and the Little Powder River, Wyoming".

Horizon: Unknown, Lance Formation?

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material: Left squamosal.

 


= Pachycephalosaurus grangeri BROWN & SCHLAIKJER, 1943
Etymology: In honor of the late Dr. Walter Granger.

Holotype: AMNH 1696

Locality: Sec. 17, T1S, R55E, William Winkley Ranch, Powder Hill, North of Ekalaka, Carter County, Montana.

Horizon: Hell Creek Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material: A nearly complete and excellently preserved skull with brain case.

Redrawn skull with pointed rear scutes.

 


= Pachycephalosaurus reinheimeri BROWN & SCHLAIKJER, 1943
Etymology: In honor of Mr. Philip Reinheimer, discoverer of the type.

Holotype: DMNH 469

Locality: Near southwest corner of sec. 25, T20N, R21E, Corson County, South Dakota.

Horizon: Lance Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material: Frontoparietal area with parts of the squamosals and nasals.