Exceptional preservation of comma shrimp from a mid-Cretaceous Lagerstätte of Colombia, and the origins of crown Cumacea
Bibliographic record
Abstract
Mesozoic rocks with exceptional preservation of marine arthropods are known worldwide but largely restricted to mid–high latitudes. The scarcity of assemblages with exceptional preservation in low, tropical latitudes greatly limits our understanding of the origins of several modern groups and the evolution of tropical biotas through time. Here, we report the oldest crown Cumacea, or ‘comma’ shrimp (Arthropoda: Eumalacostraca: Peracarida) with modern familial affinities, from a new mid-Cretaceous (95–90 Ma) Lagerstätte in tropical South America. Cumaceans have one of the poorest fossil records among marine arthropods, despite today being abundant and speciose benthic organisms associated with fine-grained sediments with high fossilization potential. Eobodotria muisca gen. et sp. nov., found in mass accumulation surfaces, preserves with detail the gut, mouth parts, thoracic legs/pereopods, pleopods, uropods bearing setae, antennal flagella and even small eyes bearing ommatidia. These features, rarely preserved in fossil crustaceans, plus the large sample size (greater than 200 individuals, 6–8 mm long), allow us to discuss phylogenetic/systematic aspects and explore possible mechanisms behind their unusual accumulation. Eobodotria bridges an approximately 165 Myr gap in the cumacean fossil record, provides a reliable calibration point for phylogenetic studies and expands our understanding of exceptional preservation in past and present tropical settings.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".