A New Specimen of Xiphiorhynchus sp. cf. aegyptiacus (Istiophoriformes, Xiphioidei, Xiphiidae) and Billfish Diversity in the Oligocene of South Carolina
Bibliographic record
Abstract
A partial billfish rostrum from the Chandler Bridge Formation (Early Chattian, Oligocene) near Ladson, South Carolina, U.S.A., is described and identified as Xiphiorhynchus sp. cf. aegyptiacus. The angle of taper, depth to width ratio of the cross section, and other morphological features (including dorsolateral grooves and a planoconvex cross-section), indicate that this specimen (and an earlier published speccimen) is closest in morphology to X. aegyptiacus from the Eocene Birket Qarun Formation of Egypt. This confirms the presence of a second xiphiid in the Chandler Bridge Formation besides the well-documented giant swordfish X. rotundus. This is an unusual example of two Xiphiorhynchus species existing in known sympatry, and strongly contrasting morphologies and morphometrics may point to niche partitioning between the two forms. The occurrence of specimens strongly resembling X. aegyptiacus in the western Atlantic also further substantiates past arguments that easy dispersal across the Atlantic was possible for this genus, and, by extension, that it shared the open-sea, migratory epipelagic lifestyle of modern swordfish. Moreover, the Chandler Bridge Formation boasts the most diverse billfish assemblage in the world, including Xiphiorhynchus sp., cf. X. aegyptiacus, X. rotundus, an early istiophorid, and 4-7 species of blochiid billfish in the genera Aglyptorhynchus and Cylindracanthus.
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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) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| 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) | 0.001 | 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 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".