Giant, swimming mouths: oral dimensions of extant sharks do not accurately predict body size in <i>Dunkleosteus terrelli</i> (Placodermi: Arthrodira)
Bibliographic record
Abstract
Background The size of Dunkleosteus and other late Devonian arthrodire placoderms has been a persistent problem in paleontology. The bony head and thoracic armor of these animals are typically the only elements preserved in the fossil record, with the rest of the body being lost during fossilization. Accurate length estimates of arthrodires are critical for reconstructing the paleobiology of these taxa and Devonian paleoecology more generally. Lengths of 5.3–8.8 m were proposed for Dunkleosteus based on allometric relationships between upper jaw perimeter and total length in extant large-bodied sharks. However, these methods were not statistically evaluated to determine if allometric relationships between body size and mouth size in sharks reliably predicted size in arthrodires. Several smaller arthrodire taxa are known from relatively complete remains, and can be used as independent case studies to test the accuracy of these methods. Results Length estimates for Dunkleosteus are evaluated through an examination of mouth proportions in complete arthrodires and fishes more generally. Currently accepted lengths of 5.3–8.8 m for D. terrelli are mathematically and biologically unlikely for three major reasons: (1) Arthrodires have larger mouths than sharks at similar body sizes. (2) upper jaw perimeter and mouth width produce extreme overestimates of body size (at least twice the actual value) in arthrodires known from complete remains. (3) Reconstructing Dunkleosteus using lengths predicted by upper jaw perimeter results in highly unusual body proportions, including extremely small, shrunken heads and hyper-anguilliform body plans, not seen in complete arthrodires or fishes more generally. Conclusions Length estimates for arthrodires based on the mouth dimensions of extant sharks are not reliable. Arthrodires have proportionally larger mouths than sharks, more similar to catfishes (Siluriformes). The disproportionately large mouths of arthrodires suggest these animals may have consumed larger prey relative to their body size than extant macropredatory sharks, and thus the paleobiology and paleoecology of these two groups may not have been exactly analogous within their respective ecosystems.
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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 | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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 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".