Pronunciation: gra-vith-O-luss
Meaning: Heavy dome
Author/s: Wall and Galton (1979)
Synonyms: None known
First Discovery: Alberta, Canada
Discovery Chart Position: #265
Gravitholus albertae
Of the hundreds of pachycephalosaurid specimens recovered from the Upper Cretaceous Belly River Group of Alberta, none have been more contentious than
Gravitholus albertae, which has caused nothing but arguments since its original description by Wall and Galton in 1979.
Its only fossil, the name-prompting heavy dome, appears to be unique (at least to some palaeontologists), but that could be because it's both terribly distorted and badly eroded. It's also heavily fused, so it's impossible to tell which of the separate skull bones were present with the naked eye, making comparisons to the corresponding bones of similar dinosaurs from the same time and place nigh on impossible.
Before it was ravaged by a tag team of Mother Nature and Old Father Time, Gravitholus may have resembled Hanssuesia sternbergi, which is itself no stranger to controversy. Unsurprisingly for Late Cretaceous "head-bangers", both have been accused of being dubious and flirted with the possibility of being synonymous with Stegoceras, in equal measure. But outside of hunches, there was no evidence to confirm or refute those theories until 2023.
Armed with synchrotron µCT scanning technology, Dyer and colleagues rammed photon beams through the skull of Gravitholus, creating an "x-ray" of the internal structure, returned as thin image slices, which allowed a comparison of its individual skull bones to those of Stegoceras. Contrary to Wall and Galton's 40-odd-year-old diagnosis, things like a relatively small braincase and significantly thicker and wider skull dome with large depressions and smaller pits on the rear were either not unique to Gravitholus or explained away as age-related or pathologies. Furthermore, its skull bones weren't particularly different in anything other than overall size.
All things considered, it appears that Gravitholus is just a very old, very large specimen of Stegoceras with a skull infection. Hanssuesia is also likely an old specimen of Stegoceras but a "late domer", with a short and shallow skull dome not yet as developed as might be expected on a specimen of its age.
Its only fossil, the name-prompting heavy dome, appears to be unique (at least to some palaeontologists), but that could be because it's both terribly distorted and badly eroded. It's also heavily fused, so it's impossible to tell which of the separate skull bones were present with the naked eye, making comparisons to the corresponding bones of similar dinosaurs from the same time and place nigh on impossible.
Before it was ravaged by a tag team of Mother Nature and Old Father Time, Gravitholus may have resembled Hanssuesia sternbergi, which is itself no stranger to controversy. Unsurprisingly for Late Cretaceous "head-bangers", both have been accused of being dubious and flirted with the possibility of being synonymous with Stegoceras, in equal measure. But outside of hunches, there was no evidence to confirm or refute those theories until 2023.
Armed with synchrotron µCT scanning technology, Dyer and colleagues rammed photon beams through the skull of Gravitholus, creating an "x-ray" of the internal structure, returned as thin image slices, which allowed a comparison of its individual skull bones to those of Stegoceras. Contrary to Wall and Galton's 40-odd-year-old diagnosis, things like a relatively small braincase and significantly thicker and wider skull dome with large depressions and smaller pits on the rear were either not unique to Gravitholus or explained away as age-related or pathologies. Furthermore, its skull bones weren't particularly different in anything other than overall size.
All things considered, it appears that Gravitholus is just a very old, very large specimen of Stegoceras with a skull infection. Hanssuesia is also likely an old specimen of Stegoceras but a "late domer", with a short and shallow skull dome not yet as developed as might be expected on a specimen of its age.
(Heavy Dome from Alberta)Etymology
Gravitholus is derived from the Latin "gravis" (heavy) and the Greek "tholos" (dome) in reference to its enlarged skull dome.The species epithet, albertae, refers to Alberta, Canada, where the specimen was found.
Discovery
Gravitholus was discovered in the Oldman Formation (Belly River Group) at Jenner Ferry, Alberta, Canada, by Mr. Malach of Ralston, Alberta.
The holotype (TMP 1972.27.1) is a skull dome.
