Endocranial Morphology of Labidolemur kayi (Apatemyidae, Apatotheria) and Its Relevance to the Study of Brain Evolution in Euarchontoglires
Bibliographic record
Abstract
ABSTRACT Apatemyids are known from the Paleocene and Eocene of Europe, and the Paleocene to Oligocene of North America, and may share a special relationship with Euarchontoglires. The only endocast previously described for an apatemyid pertains to Carcinella sigei from the late Eocene of France. Here we present a composite virtual endocast of Labidolemur kayi derived from high-resolution X-ray computed tomography data, based on partial crania from the late Paleocene (Clarkforkian) and early Eocene (Wasatchian) of the Clarks Fork Basin, Wyoming. Like C. sigei, L. kayi had voluminous, transversely expansive olfactory bulbs, accounting for approximately 12–15% of the endocranial volume. This is similar to Cretaceous eutherians, but contrasts with the relatively smaller olfactory bulbs in both the basal gliran Rhombomylus turpanensis and in primitive primates (Ignacius graybullianus, Microsyops annectens). Similar to R. turpanensis, I. graybullianus, and the inferred ancestral condition for Microsyops, but unlike C. sigei, L. kayi exhibited exposed caudal colliculi, supporting the inference that this condition was primitive for Euarchontoglires and Euarchonta. The cranial capacity of L. kayi is estimated at 0.5–0.6 cc, yielding encephalization quotient (EQ) estimates of 0.23–0.28 or 0.42–0.50 depending on the equation used. These values are much lower than estimates for C. sigei, suggesting significant increase occurred in brain size in Apatemyidae, perhaps related to elaborations in the family's specialized manual extractive feeding regime. Similarities with primitive primates in EQ and the inferred position of the rhinal sulcus may allow for inferences about encephalization and neocorticalization in the common ancestor of Euarchontoglires.
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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 | 0.000 |
| 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".