Platytholus is an extinct genus of pachycephalosaurid dinosaur from the Late Cretaceous (Maastrichtian) Hell Creek Formation of the United States. The genus contains a single species, P. clemensi, known from a partial skull.

Discovery and naming

Life restoration

The Platytholus holotype specimen, MOR 2915, was discovered during the early 2000s in sediments of the Hell Creek Formation, dated to the latest Maastrichtian age of the late Cretaceous period, in Garfield County, Montana. The specimen consists of a partial skull.

In 2023, Horner, Goodwin & Evans described Platytholus clemensi, a new genus and species of pachycephalosaurid, based on these fossil remains. The generic name, "Platytholus", combines the Latinised Greek "platys", meaning "flattened", "wide", or "broad", and "tholos", meaning a "small domed hill". The specific name, "clemensi", honors American paleontologist William A. Clemens Jr.

Classification

Horner, Goodwin & Evans (2023) recovered Platytholus as a pachycephalosaurine member of the Pachycephalosauridae, as the sister taxon to a clade formed by Prenocephale and Acrotholus. The results of their phylogenetic analyses are shown in the cladogram below:

PachycephalosauriaWannanosaurus Pachycephalosauridae Hanssuesia Colepiocephale Stegoceras Pachycephalosaurinae Goyocephale Homalocephale Tylocephale Foraminacephale Amtocephale Prenocephale Acrotholus Platytholus Sphaerotholus edmontonensis Sphaerotholus goodwini Sphaerotholus buchholtzae Pachycephalosaurus Alaskacephale
Wannanosaurus
PachycephalosauridaeHanssuesia Colepiocephale Stegoceras Pachycephalosaurinae Goyocephale Homalocephale Tylocephale Foraminacephale Amtocephale Prenocephale Acrotholus Platytholus Sphaerotholus edmontonensis Sphaerotholus goodwini Sphaerotholus buchholtzae Pachycephalosaurus Alaskacephale
Hanssuesia Colepiocephale Stegoceras
Hanssuesia
Colepiocephale
Stegoceras
PachycephalosaurinaeGoyocephale Homalocephale Tylocephale Foraminacephale Amtocephale Prenocephale Acrotholus Platytholus Sphaerotholus edmontonensis Sphaerotholus goodwini Sphaerotholus buchholtzae Pachycephalosaurus Alaskacephale
Goyocephale
Homalocephale Tylocephale Foraminacephale Amtocephale Prenocephale Acrotholus Platytholus Sphaerotholus edmontonensis Sphaerotholus goodwini Sphaerotholus buchholtzae Pachycephalosaurus Alaskacephale
Homalocephale
Tylocephale Foraminacephale Amtocephale Prenocephale Acrotholus Platytholus Sphaerotholus edmontonensis Sphaerotholus goodwini Sphaerotholus buchholtzae Pachycephalosaurus Alaskacephale
Tylocephale
Foraminacephale Amtocephale Prenocephale Acrotholus Platytholus Sphaerotholus edmontonensis Sphaerotholus goodwini Sphaerotholus buchholtzae Pachycephalosaurus Alaskacephale
Foraminacephale
Amtocephale Prenocephale Acrotholus Platytholus Sphaerotholus edmontonensis Sphaerotholus goodwini Sphaerotholus buchholtzae Pachycephalosaurus Alaskacephale
Amtocephale
Prenocephale Acrotholus Platytholus Sphaerotholus edmontonensis Sphaerotholus goodwini Sphaerotholus buchholtzae Pachycephalosaurus Alaskacephale
Prenocephale Acrotholus Platytholus Sphaerotholus edmontonensis Sphaerotholus goodwini Sphaerotholus buchholtzae Pachycephalosaurus Alaskacephale
Prenocephale Acrotholus Platytholus
Prenocephale
Acrotholus
Platytholus
Sphaerotholus edmontonensis Sphaerotholus goodwini Sphaerotholus buchholtzae Pachycephalosaurus Alaskacephale
Sphaerotholus edmontonensis
Sphaerotholus goodwini
Sphaerotholus buchholtzae
Pachycephalosaurus
Alaskacephale