Problematic putative pachycephalosaurids: Synchrotron µCT imaging shines new light on the anatomy and taxonomic validity of Gravitholus albertae from the Belly River Group (Campanian) of Alberta, Canada
Bibliographic record
Abstract
The taxonomic validity of the holotype and sole specimen of the pachycephalosaurid Gravitholus albertae (TMP 1972.027.0001) from the Belly River Group (Alberta, Canada), remains unresolved forty years after its first description. The diagnosis for this species is tenuous at best and extensive cranial fusion has prevented a thorough description and taxonomic referral of TMP 1972.027.0001. We used synchrotron µCT imaging to identify fused sutures and segment the individual elements that comprise TMP 1972.027.0001. This allowed for a detailed description of the specimen in a more thorough comparative framework with other known pachycephalosaurid specimens. Using new observations of contacts between cranial elements, the morphological distinction of TMP 1972.027.0001 from other Belly River Group pachycephalosaurids was tested with bivariate and multivariate morphometric analyses. TMP 1972.027.0001 is morphologically consistent as an end-stage semaphorant of Stegoceras validum. Furthermore, we find no taxonomically significant morphometric distinctions between Gravitholus albertae, Hanssuesia sternbergi, and Stegoceras validum, and propose the former two are synonymous with the later. Large Stegoceras validum frontoparietals show statistically significant dimorphism in the thickness of the frontonasal boss, which is not apparent amongst juvenile and subadult specimens. Pathologies consistent with intraspecific combat (“headbutting”) appear restricted to frontoparietal domes with proportionally taller frontonasal bosses, and suggests that the two morphs represent sexual dimorphs, rather than separate species. Foraminacephale brevis and Stegoceras validum are the only named pachycephalosaurids recognised in the Dinosaur Park Formation. The stratigraphic and temporal range of Stegoceras validum is extended into the underlying Oldman Formation. Pachycephalosaurid diversity in the Campanian is reduced as a result of these revised taxonomic hypotheses. A revised phylogenetic character matrix, recognising taxonomic synonymies and ontogenetically dependent character states results in a largely unresolved Pachycephalosauria.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".