Diverging trends in erythrocyte size elucidate cardiovascular evolution in stem dinosaurs and crocodilians
Bibliographic record
Abstract
Red blood cell (RBC) size constrains the rate of diffusion of gases between (i) the environment and the capillary beds of the gas exchanger and (ii) the blood and organs. In birds, small RBCs with a high surface area to volume ratio permit a high O 2 diffusion capacity and facilitate sustained, vigorous exercise. Unfortunately, our knowledge of archosaur cardiovascular evolution is incomplete without fossilized RBCs and blood vessels. However, muscle capillary diameters closely match RBC width and, importantly, these microvessels leave a signature in bone in the fossil record. Here, we ask: do fossilized, histological indicators of RBC size, combined with phylogenetic information, support divergent patterns of cardiovascular evolution in Mesozoic crocodile-line and bird-line archosaurs? Building on a published dataset, we used vasculo-lacunar histometrics and phylogeny to retrodict RBC sizes in 20 extinct and 20 extant tetrapods. Our results indicate decreases in RBC size within the archosauromorph Prolacerta and in bird-line archosaurs (Avemetatarsalia). Conversely, crocodile-line archosaurs (Pseudosuchia) that transitioned to an aquatic environment demonstrated increases in RBC size. These patterns offer an opportunity to probe physiological hypotheses regarding archosaur cardiovascular evolution and can explain, in part, the contrasting aerobic capacities of extant species in these two major archosaur lineages.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".