My theropod is bigger than yours … or not: estimating body size from skull length in theropods
Bibliographic record
Abstract
ABSTRACT To develop a widely applicable method to estimate body size in theropods, the scaling relationship between skull length, body length, and body mass was investigated using 13 strictly carnivorous, non-avialan theropod taxa ranging in size from the 1-m Sinosauropteryx prima to the 12-m Tyrannosaurus rex. Body length was obtained from the literature for complete to nearly-complete specimens and body mass was obtained from three-dimensional mathematical slicing of those same specimens to ensure accurate body length-body mass associations. Least-square regressions reveal a tight correlation between skull length and body length (SK-BL) and skull length and body mass (SK-BM). The SK-BL regression is negatively allometric, which indicates that skulls become longer relative to body length with increasing body size. In contrast, the SK-BM regression is positively allometric, indicating that body mass increases faster than skull length with increasing body size. These conclusions confirm that the common practice of scaling isometrically smaller relatives of a given taxon to obtain body length and body mass estimates is not valid. Although predictive equations derived from the regressions fail to predict accurately body size in abelisaurids and juvenile theropods due to their different head/body proportions, they produce accurate body size estimates for theropods of known body size, thus validating their applicability. Body size estimates for Carcharodontosaurus and Giganotosaurus, approaching 13 m and 14 tons, suggest that they may have surpassed Tyrannosaurus in size. A revised body size estimate for a large Spinosaurus specimen suggests a much shorter and heavier animal than recently suggested.
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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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.005 | 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".