Ontogeny and evolution of the elasmosaurid neck highlight greater diversity of Antarctic plesiosaurians
Bibliographic record
Abstract
Abstract The Antarctic plesiosaurian record is critical for understanding the evolution of elasmosaurids in the southern hemisphere. Elasmosaurids exhibit some of the most remarkable modifications of the vertebrate axial skeleton given their extreme elongation of the cervical region. Despite a considerable amount of information available on vertebral counts within Plesiosauria throughout the decades, we have a considerably more limited understanding of the diversity of cervical vertebral shapes in elasmosaurids and how these have changed throughout ontogeny and phylogeny. Here, we compile the largest known morphometric dataset on elasmosaurid cervical vertebrae, including data on juveniles and adults, to answer some of those long‐standing questions. This dataset also includes newly recovered materials from Antarctica, which we describe herein. Using multivariate statistical approaches, we find that the two major elasmosaurid cervical morphotypes, the elasmosaurine anteroposteriorly elongate (can‐shaped) and the aristonectine anteroposteriorly short and dorsoventrally tall (disc‐like), evolved towards opposite regions of the morphospace from the plesiomorphic ‘Cimoliasaurus’‐grade condition. We also find a marked ontogenetic shift from the disc‐like to can‐shaped morphology, which is especially pronounced in elasmosaurines but more limited in aristonectines. Furthermore, we find that juvenile aristonectines occupy a specific region of the vertebral morphospace, distinct from any other group or ontogenetic stage, thus suggesting that reversal to the ‘short‐necked’ condition in elasmosaurids is mostly characterized by ontogenetic predisplacement in aristonectines. Finally, we find that it is possible to discriminate between vertebral shapes of distinct taxonomic groups regardless of ontogenetic stage, and that the diversity of Antarctic elasmosaurids was greater than previously recognized.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 0.001 |
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 source (direct Gemma or distilled Codex), 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".