First record of a hybodont shark (Chondrichthyes: Hybodontiformes) from the Lower Cretaceous of Colombia
Bibliographic record
Abstract
The Mesozoic chondrichthyan fossil record from northern South America is scarce and poorly known containing only a few reports of lamniform and ptychodont species from the Upper Cretaceous of Colombia and Venezuela. Here, we report the discovery of two associated (found together) dorsal fin spines of a hybodont shark from the Valanginian deposits of the Rosablanca Formation (Andes of Colombia). This hybodont along with the presence of ammonites and other mollusks, turtles, plesiosaurs and ichthyosaurs support a marine depositional environment for this geological unit. Although both spines described here are fragmentary and without diagnostic characters to allow identification to generic level, their finding represents the first record of this shark group from northernmost part of South America and northwestern margin of Gondwana. This new record expands the known distribution of this group of sharks during Lower Cretaceous.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 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 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.009 | 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; both teacher heads agree on what is shown here.
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".