Systematics of Chasmosaurus - new information from the Peabody Museum skull, and the use of phylogenetic analysis for dinosaur alpha taxonomy
Bibliographic record
Abstract
<ns4:p> The horned dinosaur <ns4:italic>Chasmosaurus</ns4:italic> from the late Campanian Dinosaur Park Formation of Alberta, is known from numerous skulls and skeletons, but over a century after its description, the taxonomy of the genus is controversial. Two species, <ns4:italic>Chasmosaurus belli</ns4:italic> and <ns4:italic>C. russelli</ns4:italic> , are currently recognized, with a third species, <ns4:italic>C. irvinensis</ns4:italic> , recently placed in a new genus, <ns4:italic>Vagaceratops</ns4:italic> . Here, the Yale <ns4:italic>Chasmosaurus</ns4:italic> skull is described, and implications for <ns4:italic>Chasmosaurus</ns4:italic> systematics are explored. The Yale skull is intermediate between typical <ns4:italic>C. belli</ns4:italic> and <ns4:italic>C. irvinensis</ns4:italic> . <ns4:italic>C.</ns4:italic> <ns4:italic>belli</ns4:italic> -like features include large, triangular lateral epiparietals, large parietal fenestrae, and an emarginate parietal. Yet the skull also exhibits derived features of <ns4:italic>C. irvinensis</ns4:italic> , including a posteriorly inclined narial strut, brow horns replaced by rugose bosses, reduced parietal emargination, five pairs of epiparietals, and epiparietals that fuse at their bases and hook forward over the frill. Specimen-level phylogenetic analysis provides a hypothesis of relationships upon which to base the taxonomy of <ns4:italic>Chasmosaurus</ns4:italic> . <ns4:italic>C. belli</ns4:italic> is paraphyletic with respect to <ns4:italic>C. irvinensis</ns4:italic> , and the Peabody skull is closer to <ns4:italic>C. irvinensis</ns4:italic> than to other <ns4:italic>C. belli</ns4:italic> . The holotype of <ns4:italic>C. russelli</ns4:italic> clusters with <ns4:italic>C. belli</ns4:italic> , making <ns4:italic>C. russelli</ns4:italic> a junior synonym of <ns4:italic>C</ns4:italic> . <ns4:italic>belli</ns4:italic> . Accordingly, <ns4:italic>Chasmosaurus</ns4:italic> can be divided into three species: <ns4:italic>C. belli</ns4:italic> , <ns4:italic>C. irvinensis</ns4:italic> , and <ns4:italic>C. priscus</ns4:italic> sp. nov, including specimens previously referred to <ns4:italic>C</ns4:italic> . <ns4:italic>russelli</ns4:italic> . The systematics of <ns4:italic>Chasmosaurus</ns4:italic> show how specimen level phylogeny can provide an evolutionary framework upon which to establish taxonomies. However, the resulting phylogenies may lead to paraphyletic species and genera. </ns4:p>
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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 | 0.002 | 0.001 |
| 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) | 0.000 | 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".