Palaeohistology and life history of the early Palaeocene taeniodont <i>Conoryctes comma</i> (Mammalia: Eutheria)
Bibliographic record
Abstract
The life histories of Palaeocene mammals are poorly known, but may have been central to their success in diversifying across terrestrial ecosystems after the end-Cretaceous extinction. Among these mammalian groups, the eutherian Taeniodonta are particularly enigmatic, with few modern analogues and no living descendants, despite being one of the only lineages to apparently traverse the Cretaceous-Palaeogene (K-Pg) boundary. Here, we investigate the life history of an early Palaeocene taeniodont, Conoryctes comma, based on a multi-individual, multi-element sample. Nearly all elements sampled exhibit similar osteohistological architecture, with a small internal zone of compacted coarse cancellous bone surrounded by an internal cortex of periosteally derived fibrolamellar bone of variable thickness, and an outer cortex of lamellar bone. The well-vascularized fibrolamellar complex in the limb bones, lacking cyclical growth marks, is indicative of overall rapid growth to near adult body size. Cyclical growth marks are present in the outer cortex after the transition to slow-growing lamellar bone, but not in the inner cortex, suggesting sexual maturity was reached in 1 year. In some elements, an internal non-cyclical growth mark shares histological similarities with weaning marks in living mammals and other contemporary Palaeocene mammals, and occurred at the body size predicted for this transition in therian mammals. The unusual presence of compacted coarse cancellous bone near the midshafts of multiple limb bones may be related to cortical thickening, and is similar to the arrangement described in some fossorial mammals, supporting previous assertions of this lifestyle in Conoryctes. Altogether, these palaeohistological signals suggest a life history in C. comma similar to living eutherians, despite uncertainty about whether it is within crown Placentalia or a close outgroup. Thus, our data are consistent with an early origin of placental-like reproductive strategies in their eutherian ancestors, although this attribute was likely shared more broadly among Mesozoic mammal lineages prior to the end-Cretaceous extinction.
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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 | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 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".